In a garbage collector that more efficiently places newly promoted objects into a generation managed by the train algorithm, a promotion train is established near the oldest train and the objects are placed therein. If some objects are referenced from existing trains in the generation those objects are placed into those trains, and if any such objects are referenced from several existing trains, the objects are placed at the end of the youngest referencing train. The promotion train may be a new train that is placed, or a existing train that is selected, between the oldest train and the youngest train at a position based on the amount of memory compared to the size of a collection set. In the case of multiple collector threads, multiple cars in a promotion train or multiple promotion trains may be formed.

1. Field of the Invention
The present invention is directed to memory management. It particularly concerns what has come to be known as "garbage collection."
2. Background Information
In the field of computer systems, considerable effort has been expended on the task of allocating memory to data objects. For the purposes of this discussion, the term object refers to a data structure represented in a computer system's memory. Other terms sometimes used for the same concept are record and structure. An object may be identified by a reference, a relatively small amount of information that can be used to access the object. A reference can be represented as a "pointer" or a "machine address," which may require, for instance, only sixteen, thirty-two, or sixty-four bits of information, although there are other ways to represent a reference.
In some systems, which are usually known as "object oriented," objects may have associated methods, which are routines that can be invoked by reference to the object. They also may belong to a class, which is an organizational entity that may contain method code or other information shared by all objects belonging to that class. In the discussion that follows, though, the term object will not be limited to such structures; it will additionally include structures with which methods and classes are not associated.
The invention to be described below is applicable to systems that allocate memory to objects dynamically. Not all systems employ dynamic allocation. In some computer languages, source programs must be so written that all objects to which the program's variables refer are bound to storage locations at compile time. This storage-allocation approach, sometimes referred to as "static allocation," is the policy traditionally used by the Fortran programming language, for example.
Even for compilers that are thought of as allocating objects only statically, of course, there is often a certain level of abstraction to this binding of objects to storage locations. Consider the typical computer system 10 depicted in FIG. 1, for example. Data, and instructions for operating on them, that a microprocessor 11 uses may reside in on-board cache memory or be received from further cache memory 12, possibly through the mediation of a cache controller 13. That controller 13 can in turn receive such data from system read/write memory ("RAM") 14 through a RAM controller 15 or from various peripheral devices through a system bus 16. The memory space made available to an application program may be "virtual" in the sense that it may actually be considerably larger than RAM 14 provides. So the RAM contents will be swapped to and from a system disk 17.
Additionally, the actual physical operations performed to access some of the most-recently visited parts of the process's address space often will actually be performed in the cache 12 or in a cache on board microprocessor 11 rather than on the RAM. 14, with which those caches swap data and instructions just as RAM 14 and system disk 17 do with each other.
A further level of abstraction results from the fact that an application will often be run as one of many processes operating concurrently with the support of an underlying operating system. As part of that system's memory management, the application's memory space may be moved among different actual physical locations many times in order to allow different processes to employ shared physical memory devices. That is, the location specified in the application's machine code may actually result in different physical locations at different times because the operating system adds different offsets to the machine-language-specified location.
Despite these expedients, the use of static memory allocation in writing certain long-lived applications makes it difficult to restrict storage requirements to the available memory space. Abiding by space limitations is easier when the platform provides for dynamic memory allocation, i.e., when memory space to be allocated to a given object is determined only at run time.
Dynamic allocation has a number of advantages, among which is that the run-time system is able to adapt allocation to run-time conditions. For example, the programmer can specify that space should be allocated for a given object only in response to a particular run-time condition. The C-language library function malloc( ) is often used for this purpose. Conversely, the programmer can specify conditions under which memory previously allocated to a given object can be reclaimed for reuse. The C-language library function free( ) results in such memory reclamation.
Because dynamic allocation provides for memory reuse, it facilitates generation of large or long-lived applications, which over the course of their lifetimes may employ objects whose total memory requirements would greatly exceed the available memory resources if they were bound to memory locations statically.
Particularly for long-lived applications, though, allocation and reclamation of dynamic memory must be performed carefully. If the application fails to reclaim unused memory—or, worse, loses track of the address of a dynamically allocated segment of memory—its memory requirements will grow over time to exceed the system's available memory. This kind of error is known as a "memory leak."
Another kind of error occurs when an application reclaims memory for reuse even though it still maintains a reference to that memory. If the reclaimed memory is reallocated for a different purpose, the application may inadvertently manipulate the same memory in multiple inconsistent ways. This kind of error is known as a "dangling reference," because an application should not retain a reference to a memory location once that location is reclaimed. Explicit dynamic-memory management by using interfaces like malloc( )/free( ) often leads to these problems.
A way of reducing the likelihood of such leaks and related errors is to provide memory-space reclamation in a more-automatic manner. Techniques used by systems that reclaim memory space automatically are commonly referred to as "garbage collection." Garbage collectors operate by reclaiming space that they no longer consider "reachable." Statically allocated objects represented by a program's global variables are normally considered reachable throughout a program's life. Such objects are not ordinarily stored in the garbage collector's managed memory space, but they may contain references to dynamically allocated objects that are, and such objects are considered reachable. Clearly, an object referred to in the processor's call stack is reachable, as is an object referred to by register contents. And an object referred to by any reachable object is also reachable.
The use of garbage collectors is advantageous because, whereas a programmer working on a particular sequence of code can perform his task creditably in most respects with only local knowledge of the application at any given time, memory allocation and reclamation require a global knowledge of the program. Specifically, a programmer dealing with a given sequence of code does tend to know whether some portion of memory is still in use for that sequence of code, but it is considerably more difficult for him to know what the rest of the application is doing with that memory. By tracing references from some conservative notion of a "root set," e.g., global variables, registers, and the call stack, automatic garbage collectors obtain global knowledge in a methodical way. By using a garbage collector, the programmer is relieved of the need to worry about the application's global state and can concentrate on local-state issues, which are more manageable. The result is applications that are more robust, having no dangling references and fewer memory leaks.
Garbage-collection mechanisms can be implemented by various parts and levels of a computing system. One approach is simply to provide them as part of a batch compiler's output. Consider FIG. 2's simple batch-compiler operation, for example. A computer system executes in accordance with compiler object code and therefore acts as a compiler 20. The compiler object code is typically stored on a medium such as FIG. 1's system disk 17 or some other machine-readable medium, and it is loaded into RAM 14 to configure the computer system to act as a compiler. In some cases, though, the compiler object code's persistent storage may instead be provided in a server system remote from the machine that performs the compiling. The electrical signals that carry the digital data by which the computer systems exchange that code are examples of the kinds of electromagnetic signals by which the computer instructions can be communicated. Others are radio waves, microwaves, and both visible and invisible light.
The input to the compiler is the application source code, and the end product of the compiler process is application object code. This object code defines an application 21, which typically operates on input such as mouse clicks, etc., to generate a display or some other type of output. This object code implements the relationship that the programmer intends to specify by his application source code. In one approach to garbage collection, the compiler 20, without the programmer's explicit direction, additionally generates code that automatically reclaims unreachable memory space.
Even in this simple case, though there is a sense in which the application does not itself provide the entire garbage collector. Specifically, the application will typically call upon the underlying operating system's memory-allocation functions. And the operating system may in turn take advantage of various hardware that lends itself particularly to use in garbage collection. So even a very simple system may disperse the garbage-collection mechanism over a number of computer-system layers.
To get some sense of the variety of system components that can be used to implement garbage collection, consider FIG. 3's example of a more complex way in which various levels of source code can result in the machine instructions that a processor executes. In the FIG. 3 arrangement, the human applications programmer produces source code 22 written in a high-level language. A compiler 23 typically converts that code into "class files." These files include routines written in instructions, called "byte codes" 24, for a "virtual machine" that various processors can be software-configured to emulate. This conversion into byte codes is almost always separated in time from those codes' execution, so FIG. 3 divides the sequence into a "compile-time environment" 25 separate from a "run-time environment" 26, in which execution occurs. One example of a high-level language for which compilers are available to produce such virtual-machine instructions is the Java™ programming language. (Java is a trademark or registered trademark of Sun Microsystems, Inc., in the United States and other countries.)
Most typically, the class files' byte-code routines are executed by a processor under control of a virtual-machine process 27. That process emulates a virtual machine from whose instruction set the byte codes are drawn. As is true of the compiler 23, the virtual-machine process 27 may be specified by code stored on a local disk or some other machine-readable medium from which it is read into FIG. 1's RAM 14 to configure the computer system to implement the garbage collector and otherwise act as a virtual machine. Again, though, that code's persistent storage may instead be provided by a server system remote from the processor that implements the virtual machine, in which case the code would be transmitted electrically or optically to the virtual-machine-implementing processor.
In some implementations, much of the virtual machine's action in executing these byte codes is most like what those skilled in the art refer to as "interpreting," so FIG. 3 depicts the virtual machine as including an "interpreter" 28 for that purpose. In addition to or instead of running an interpreter, many virtual-machine implementations actually compile the byte codes concurrently with the resultant object code's execution, so FIG. 3 depicts the virtual machine as additionally including a "just-in-time" compiler 29. We will refer to the just-in-time compiler and the interpreter together as "execution engines" since they are the methods by which byte code can be executed.
Now, some of the functionality that source-language constructs specify can be quite complicated, requiring many machine-language instructions for their implementation. One quite-common example is a source-language instruction that calls for 64-bit arithmetic on a 32-bit machine. More germane to the present invention is the operation of dynamically allocating space to a new object; the allocation of such objects must be mediated by the garbage collector.
In such situations, the compiler may produce "inline" code to accomplish these operations. That is, all object-code instructions for carrying out a given source-code-prescribed operation will be repeated each time the source code calls for the operation. But inlining runs the risk that "code bloat" will result if the operation is invoked at many source-code locations.
The natural way of avoiding this result is instead to provide the operation's implementation as a procedure, i.e., a single code sequence that can be called from any location in the program. In the case of compilers, a collection of procedures for implementing many types of source-code-specified operations is called a runtime system for the language. The execution engines and the runtime system of a virtual machine are designed together so that the engines "know" what runtime-system procedures are available in the virtual machine (and on the target system if that system provides facilities that are directly usable by an executing virtual-machine program.) So, for example, the just-in-time compiler 29 may generate native code that includes calls to memory-allocation procedures provided by the virtual machine's runtime system. These allocation routines may in turn invoke garbage-collection routines of the runtime system when there is not enough memory available to satisfy an allocation. To represent this fact, FIG. 3 includes block 30 to show that the compiler's output makes calls to the runtime system as well as to the operating system 31, which consists of procedures that are similarly system-resident but are not compiler-dependent.
Although the FIG. 3 arrangement is a popular one, it is by no means universal, and many further implementation types can be expected. Proposals have even been made to implement the virtual machine 27's behavior in a hardware processor, in which case the hardware itself would provide some or all of the garbage-collection function.
The arrangement of FIG. 3 differs from FIG. 2 in that the compiler 23 for converting the human programmer's code does not contribute to providing the garbage-collection function; that results largely from the virtual machine 27's operation. Those skilled in that art will recognize that both of these organizations are merely exemplary, and many modern systems employ hybrid mechanisms, which partake of the characteristics of traditional compilers and traditional interpreters both.
The invention to be described below is applicable independently of whether a batch compiler, a just-in-time compiler, an interpreter, or some hybrid is employed to process source code. In the remainder of this application, therefore, we will use the term compiler to refer to any such mechanism, even if it is what would more typically be called an interpreter.
In short, garbage collectors can be implemented in a wide range of combinations of hardware and/or software. As is true of most of the garbage-collection techniques described in the literature, the invention to be described below is applicable to most such systems.
By implementing garbage collection, a computer system can greatly reduce the occurrence of memory leaks and other software deficiencies in which human programming frequently results. But it can also have significant adverse performance effects if it is not implemented carefully. To distinguish the part of the program that does "useful" work from that which does the garbage collection, the term mutator is sometimes used in discussions of these effects; from the collector's point of view, what the mutator does is mutate active data structures' connectivity.
Some garbage-collection approaches rely heavily on interleaving garbage-collection steps among mutator steps. In one type of garbage-collection approach, for instance, the mutator operation of writing a reference is followed immediately by garbage-collector steps used to maintain a reference count in that object's header, and code for subsequent new-object storage includes steps for finding space occupied by objects whose reference count has fallen to zero. Obviously, such an approach can slow mutator operation significantly.
Other approaches therefore interleave very few garbage-collector-related instructions into the main mutator process but instead interrupt it from time to time to perform garbage-collection cycles, in which the garbage collector finds unreachable objects and reclaims their memory space for reuse. Such an approach will be assumed in discussing FIG. 4's depiction of a simple garbage-collection operation. Within the memory space allocated to a given application is a part 40 managed by automatic garbage collection. In the following discussion, this will be referred to as the "heap," although in other contexts that term refers to all dynamically allocated memory. During the course of the application's execution, space is allocated for various objects 42, 44, 46, 48, and 50. Typically, the mutator allocates space within the heap by invoking the garbage collector, which at some level manages access to the heap. Basically, the mutator asks the garbage collector for a pointer to a heap region where it can safely place the object's data. The garbage collector keeps track of the fact that the thus-allocated region is occupied. It will refrain from allocating that region in response to any other request until it determines that the mutator no longer needs the region allocated to that object.
Garbage collectors vary as to which objects they consider reachable and unreachable. For the present discussion, though, an object will be considered "reachable" if it is referred to, as object 42 is, by a reference in the root set 52. The root set consists of reference values stored in the mutator's threads' call stacks, the CPU registers, and global variables outside the garbage-collected heap. An object is also reachable if it is referred to, as object 46 is, by another reachable object (in this case, object 42). Objects that are not reachable can no longer affect the program, so it is safe to re-allocate the memory spaces that they occupy.
A typical approach to garbage collection is therefore to identify all reachable objects and reclaim any previously allocated memory that the reachable objects do not occupy. A typical garbage collector may identify reachable objects by tracing references from the root set 52. For the sake of simplicity, FIG. 4 depicts only one reference from the root set 52 into the heap 40. (Those skilled in the art will recognize that there are many ways to identify references, or at least data contents that may be references.) The collector notes that the root set points to object 42, which is therefore reachable, and that reachable object 42 points to object 46, which therefore is also reachable. But those reachable objects point to no other objects, so objects 44, 48, and 50 are all unreachable, and their memory space may be reclaimed. This may involve, say, placing that memory space in a list of free memory blocks.
To avoid excessive heap fragmentation, some garbage collectors additionally relocate reachable objects. FIG. 5 shows a typical approach. The heap is partitioned into two halves, hereafter called "semi-spaces." For one garbage-collection cycle, all objects are allocated in one semi-space 54, leaving the other semi-space 56 free. When the garbage-collection cycle occurs, objects identified as reachable are "evacuated" to the other semi-space 56, so all of semi-space 54 is then considered free. Once the garbage-collection cycle has occurred, all new objects are allocated in the lower semi-space 56 until yet another garbage-collection cycle occurs, at which time the reachable objects are evacuated back to the upper semi-space 54.
Although this relocation requires the extra steps of copying the reachable objects and updating references to them, it tends to be quite efficient, since most new objects quickly become unreachable so most of the current semi-space is actually garbage. That is, only a relatively few, reachable objects need to be relocated, after which the entire semi-space contains only garbage and can be pronounced free for reallocation.
Now, a collection cycle can involve following all reference chains from the basic root set—i.e., from inherently reachable locations such as the call stacks, class statics and other global variables, and registers—and reclaiming all space occupied by objects not encountered in the process. And the simplest way of performing such a cycle is to interrupt the mutator to provide a collector interval in which the entire cycle is performed before the mutator resumes. For certain types of applications, this approach to collection-cycle scheduling is acceptable and, in fact, highly efficient.
For many interactive and real-time applications, though, this approach is not acceptable. The delay in mutator operation that the collection cycle's execution causes can be annoying to a user and can prevent a real-time application from responding to its environment with the required speed. In some applications, choosing collection times opportunistically can reduce this effect. Collection intervals can be inserted when an interactive mutator reaches a point at which it awaits user input, for instance.
So it may often be true that the garbage-collection operation's effect on performance can depend less on the total collection time than on when collections actually occur. But another factor that often is even more determinative is the duration of any single collection interval, i.e., how long the mutator must remain quiescent at any one time. In an interactive system, for instance, a user may never notice hundred-millisecond interruptions for garbage collection, whereas most users would find interruptions lasting for two seconds to be annoying.
The cycle may therefore be divided up among a plurality of collector intervals. When a collection cycle is divided up among a plurality of collection intervals, it is only after a number of intervals that the collector will have followed all reference chains and be able to identify as garbage any objects not thereby reached. This approach is more complex than completing the cycle in a single collection interval; the mutator will usually modify references between collection intervals, so the collector must repeatedly update its view of the reference graph in the midst of the collection cycle. To make such updates practical, the mutator must communicate with the collector to let it know what reference changes are made between intervals.
An even more complex approach, which some systems use to eliminate discrete pauses or maximize resource-use efficiency, is to execute the mutator and collector in concurrent execution threads. Most systems that use this approach use it for most but not all of the collection cycle; the mutator is usually interrupted for a short collector interval, in which a part of the collector cycle takes place without mutation.
Independent of whether the collection cycle is performed concurrently with mutator operation, is completed in a single interval, or extends over multiple intervals is the question of whether the cycle is complete, as has tacitly been assumed so far, or is instead "incremental." In incremental collection, a collection cycle constitutes only an increment of collection: the collector does not follow all reference chains from the basic root set completely. Instead, it concentrates on only a portion, or collection set, of the heap. Specifically, it identifies every collection-set object referred to by a reference chain that extends into the collection set from outside of it, and it reclaims the collection-set space not occupied by such objects, possibly after evacuating them from the collection set.
By thus culling objects referenced by reference chains that do not necessarily originate in the basic root set, the collector can be thought of as expanding the root set to include as roots some locations that may not be reachable. Although incremental collection thereby leaves "floating garbage," it can result in relatively low pause times even if entire collection increments are completed during respective single collection intervals.
Most collectors that employ incremental collection operate in "generations," although this is not necessary in principle. Different portions, or generations, of the heap are subject to different collection policies. New objects are allocated in a "young" generation, and older objects are promoted from younger generations to older or more "mature" generations. Collecting the younger generations more frequently than the others yields greater efficiency because the younger generations tend to accumulate garbage faster; newly allocated objects tend to "die," while older objects tend to "survive."
But generational collection greatly increases what is effectively the root set for a given generation. Consider FIG. 6, which depicts a heap as organized into three generations 58, 60, and 62. Assume that generation 60 is to be collected. The process for this individual generation may be more or less the same as that described in connection with FIGS. 4 and 5 for the entire heap, with one major exception. In the case of a single generation, the root set must be considered to include not only the call stack, registers, and global variables represented by set 52 but also objects in the other generations 58 and 62, which themselves may contain references to objects in generation 60. So pointers must be traced not only from the basic root set 52 but also from objects within the other generations.
One could perform this tracing by simply inspecting all references in all other generations at the beginning of every collection interval, and it turns out that this approach is actually feasible in some situations. But it takes too long in other situations, so workers in this field have employed a number of approaches to expediting reference tracing. One approach is to include so-called write barriers in the mutator process. A write barrier is code added to a write operation to record information from which the collector can determine where references were written or may have been since the last collection interval. A reference list can then be maintained by taking such a list as it existed at the end of the previous collection interval and updating it by inspecting only locations identified by the write barrier as possibly modified since the last collection interval.
One of the many write-barrier implementations commonly used by workers in this art employs what has been referred to as the "card table." FIG. 6 depicts the various generations as being divided into smaller sections, known for this purpose as "cards." Card tables 64, 66, and 68 associated with respective generations contain an entry for each of their cards. When the mutator writes a reference in a card, it makes an appropriate entry in the card-table location associated with that card (or, say, with the card in which the object containing the reference begins). Most write-barrier implementations simply make a Boolean entry indicating that the write operation has been performed, although some may be more elaborate. The mutator having thus left a record of where new or modified references may be, the collector can thereafter prepare appropriate summaries of that information, as will be explained in due course. For the sake of concreteness, we will assume that the summaries are maintained by steps that occur principally at the beginning of each collection interval.
Of course, there are other write-barrier approaches, such as simply having the write barrier add to a list of addresses where references where written. Also, although there is no reason in principle to favor any particular number of generations, and although FIG. 6 shows three, most generational garbage collectors have only two generations, of which one is the young generation and the other is the mature generation. Moreover, although FIG. 6 shows the generations as being of the same size, a more-typical configuration is for the young generation to be considerably smaller. Finally, although we assumed for the sake of simplicity that collection during a given interval was limited to only one generation, a more-typical approach is actually to collect the whole young generation at every interval but to collect the mature one less frequently.
Some collectors collect the entire young generation in every interval and may thereafter perform mature-generation collection in the same interval. It may therefore take relatively little time to scan all young-generation objects remaining after young-generation collection to find references into the mature generation. Even when such collectors do use card tables, therefore, they often do not use them for finding young-generation references that refer to mature-generation objects. On the other hand, laboriously scanning the entire mature generation for references to young-generation (or mature-generation) objects would ordinarily take too long, so the collector uses the card table to limit the amount of memory it searches for mature-generation references.
Now, although it typically takes very little time to collect the young generation, it may take more time than is acceptable within a single garbage-collection cycle to collect the entire mature generation. So some garbage collectors may collect the mature generation incrementally; that is, they may perform only a part of the mature generation's collection during any particular collection cycle. Incremental collection presents the problem that, since the generation's unreachable objects outside the "collection set" of objects processed during that cycle cannot be recognized as unreachable, collection-set objects to which they refer tend not to be, either.
To reduce the adverse effect-this would otherwise have on collection efficiency, workers in this field have employed the "train algorithm," which FIG. 7 depicts. A generation to be collected incrementally is divided into sections, which for reasons about to be described are referred to as "car sections." Conventionally, a generation's incremental collection occurs in fixed-size sections, and a car section's size is that of the generation portion to be collected during one cycle.
The discussion that follows will occasionally employ the nomenclature in the literature by using the term car instead of car section. But the literature seems to use that term to refer variously not only to memory sections themselves but also to data structures that the train algorithm employs to manage them when they contain objects, as well as to the more-abstract concept that the car section and managing data structure represent in discussions of the algorithm. So the following discussion will more frequently use the expression car section to emphasize the actual sections of memory space for whose management the car concept is employed.
According to the train algorithm, the car sections are grouped into "trains," which are ordered, conventionally according to age. For example, FIG. 7 shows an oldest train 73 consisting of a generation 74's three car sections described by associated data structures 75, 76, and 78, while a second train 80 consists only of a single car section, represented by structure 82, and the youngest train 84 (referred to as the "allocation train") consists of car sections that data structures 86 and 88 represent. As will be seen below, car sections' train memberships can change, and any car section added to a train is typically added to the end of a train.
Conventionally, the car collected in an increment is the one added earliest to the oldest train, which in this case is car 75. All of the generation's cars can thus be thought of as waiting for collection in a single long line, in which cars are ordered in accordance with the order of the trains to which they belong and, within trains, in accordance with the order in which they were added to those trains.
As is usual, the way in which reachable objects are identified is to determine whether there are references to them in the root set or in any other object already determined to be reachable. In accordance with the train algorithm, the collector additionally performs a test to determine whether there are any references at all from outside the oldest train to objects within it. If there are not, then all cars within the train can be reclaimed, even though not all of those cars are in the collection set. And the train algorithm so operates that inter-car references tend to be grouped into trains, as will now be explained.
To identify references into the car from outside of it, train-algorithm implementations typically employ "remembered sets." As card tables are, remembered sets are used to keep track of references. Whereas a card-table entry contains information about references that the associated card contains, though, a remembered set associated with a given region contains information about references into that region from locations outside of it. In the case of the train algorithm, remembered sets are associated with car sections. Each remembered set, such as car 75's remembered set 90, lists locations in the generation that contain references into the associated car section.
The remembered sets for all of a generation's cars are typically updated at the start of each collection cycle. To illustrate how such updating and other collection operations may be carried out, FIGS. 8A and 8B (together, "FIG. 8") depict an operational sequence in a system of the typical type mention above. That is, it shows a sequence of operations that may occur in a system in which the entire garbage-collected heap is divided into two generations, namely, a young generation and an old generation, and in which the young generation is much smaller than the old generation. FIG. 8 is also based on the assumption and that the train algorithm is used only for collecting the old generation.
Block 102 represents a period of the mutator's operation. As was explained above, the mutator makes a card-table entry to identify any card that it has "dirtied" by adding or modifying a reference that the card contains. At some point, the mutator will be interrupted for collector operation. Different implementations employ different events to trigger such an interruption, but we will assume for the sake of concreteness that the system's dynamic-allocation routine causes such interruptions when no room is left in the young generation for any further allocation. A dashed line 103 represents the transition from mutator operation and collector operation.
In the system assumed for the FIG. 8 example, the collector collects the (entire) young generation each time such an interruption occurs. When the young generation's collection ends, the mutator operation usually resumes, without the collector's having collected any part of the old generation. Once in a while, though, the collector also collects part of the old generation, and FIG. 8 is intended to illustrate such an occasion.
When the collector's interval first starts, it first processes the card table, in an operation that block 104 represents. As was mentioned above, the collector scans the "dirtied" cards for references into the young generation. If a reference is found, that fact is memorialized appropriately. If the reference refers to a young-generation object, for example, an expanded card table may be used for this purpose. For each card, such an expanded card table might include a multi-byte array used to summarize the card's reference contents. The summary may, for instance, be a list of offsets that indicate the exact locations within the card of references to young-generation objects, or it may be a list of fine-granularity "sub-cards" within which references to young-generation objects may be found. If the reference refers to an old-generation object, the collector often adds an entry to the remembered set associated with the car containing that old-generation object. The entry identifies the reference's location, or at least a small region in which the reference can be found. For reasons that will become apparent, though, the collector will typically not bother to place in the remembered set the locations of references from objects in car sections farther forward in the collection queue than the referred-to object, i.e., from objects in older trains or in cars added earlier to the same train.
The collector then collects the young generation, as block 105 indicates. (Actually, young-generation collection may be interleaved with the dirty-region scanning, but the drawing illustrates it for purpose of explanation as being separate.) If a young-generation object is referred to by a reference that card-table scanning has revealed, that object is considered to be potentially reachable, as is any young-generation object referred to by a reference in the root set or in another reachable young-generation object. The space occupied by any young-generation object thus considered reachable is withheld from reclamation. For example, it may be evacuated to a young-generation semi-space that will be used for allocation during the next mutator interval. It may instead be promoted into the older generation, where it is placed into a car containing a reference to it or into a car in the last train. Or some other technique may be used to keep the memory space it occupies off the system's free list. The collector then reclaims any young-generation space occupied by any other objects, i.e., by any young-generation objects not identified as transitively reachable through references located outside the young generation.
The collector then performs the train algorithm's central test, referred to above, of determining whether there are any references into the oldest train from outside of it. As was mentioned above, the actual process of determining, for each object, whether it can be identified as unreachable is performed for only a single car section in any cycle. In the absence of features such as those provided by the train algorithm, this would present a problem, because garbage structures may be larger than a car section. Objects in such structures would therefore (erroneously) appear reachable, since they are referred to from outside the car section under consideration. But the train algorithm additionally keeps track of whether there are any references into a given car from outside the train to which it belongs and trains' sizes are not limited; As will be apparent presently, objects not found to be unreachable are relocated in such a way that garbage structures tend to be gathered into respective trains into which, eventually, no references from outside the train point. If no references from outside the train point to any objects inside the train, the train can be recognized as containing only garbage. This is the test that block 106 represents. All cars in a train thus identified as containing only garbage can be reclaimed.
The question of whether old-generation references point into the train from outside of it is (conservatively) answered in the course of updating remembered sets; in the course of updating a car's remembered set, it is a simple matter to flag the car as being referred to from outside the train. The step-106 test additionally involves determining whether any references from outside the old generation point into the oldest train. Various approaches to making this determination have been suggested, including the conceptually simple approach of merely following all reference chains from the root set until those chains (1) terminate, (2) reach an old-generation object outside the oldest train, or (3) reach an object in the oldest train. In the two-generation example, most of this work can be done readily by identifying references into the collection set from live young-generation objects during the young-generation collection. If one or more such chains reach the oldest train, that train includes reachable objects. It may also include reachable objects if the remembered-set-update operation has found one or more references into the oldest train from outside of it. Otherwise, that train contains only garbage, and the collector reclaims all of its car sections for reuse, as block 107 indicates. The collector may then return control to the mutator, which resumes execution, as FIG. 8B's block 108 indicates.
If the train contains reachable objects, on the other hand, the collector turns to evacuating potentially reachable objects from the collection set. The first operation, which block 110 represents, is to remove from the collection set any object that is reachable from the root set by way of a reference chain that does not pass through the part of the old generation that is outside of the collection set. In the illustrated arrangement, in which there are only two generations, and the young generation has previously been completely collected during the same interval, this means evacuating from a collection set any object that (1) is directly referred to by a reference in the root set, (2) is directly referred to by a reference in the young generation (in which no remaining objects have been found unreachable), or (3) is referred to by any reference in an object thereby evacuated. All of the objects thus evacuated are placed in cars in the youngest train, which was newly created during the collection cycle. Certain of the mechanics involved in the evacuation process are described in more detail in connection with similar evacuation performed, as blocks 112 and 114 indicate, in response to remembered-set entries.
FIG. 9 illustrates how the processing represented by block 114 proceeds. The entries identify heap regions, and, as block 116 indicates, the collector scans the thus-identified heap regions to find references to locations in the collection-set. As blocks 118 and 120 indicate, that entry's processing continues until the collector finds no more such references. Every time the collector does find such a reference, it checks to determine whether, as a result of a previous entry's processing, the referred-to object has already been evacuated. If it has not, the collector evacuates the referred-to object to a (possibly new) car in the train containing the reference, as blocks 122 and 124 indicate.
As FIG. 10 indicates, the evacuation operation includes more than just object relocation, which block 126 represents. Once the object has been moved, the collector places a forwarding pointer in the collection-set location from which it was evacuated, for a purpose that will become apparent presently. Block 128 represents that step. (Actually, there are some cases in which the evacuation is only a "logical" evacuation: the car containing the object is simply re-linked to a different logical place in the collection sequence, but its address does not change. In such cases, forwarding pointers are unnecessary.) Additionally, the reference in response to which the object was evacuated is updated to point to the evacuated object's new location, as block 130 indicates. And, as block 132 indicates, any reference contained in the evacuated object is processed, in an operation that FIGS. 11A and 11B (together, "FIG. 11") depict.
For each one of the evacuated object's references, the collector checks to see whether the location that it refers to is in the collection set. As blocks 134 and 136 indicate, the reference processing continues until all references in the evacuated object have been processed. In the meantime, if a reference refers to a collection-set location that contains an object not yet evacuated, the collector evacuates the referred-to object to the train to which the evacuated object containing the reference was evacuated, as blocks 138 and 140 indicate.
If the reference refers to a location in the collection set from which the object has already been evacuated, then the collector uses the forwarding pointer left in that location to update the reference, as block 142 indicates. Before the processing of FIG. 11, the remembered set of the referred-to object's car will have an entry that identifies the evacuated object's old location as one containing a reference to the referred-to object. But the evacuation has placed the reference in a new location, for which the remembered set of the referred-to object's car may not have an entry. So, if that new location is not as far forward as the referred-to object, the collector adds to that remembered set an entry identifying the reference's new region, as blocks 144 and 146 indicate. As the drawings show, the same type of remembered-set update is performed if the object referred to by the evacuated reference is not in the collection set.
Now, some train-algorithm implementations postpone processing of the references contained in evacuated collection-set objects until after all directly reachable collection-set objects have been evacuated. In the implementation that FIG. 10 illustrates, though, the processing of a given evacuated object's references occurs before the next object is evacuated. So FIG. 11's blocks 134 and 148 indicate that the FIG. 11 operation is completed when all of the references contained in the evacuated object have been processed. This completes FIG. 10's object-evacuation operation, which FIG. 9's block 124 represents.
As FIG. 9 indicates, each collection-set object referred to by a reference in a remembered-set-entry-identified location is thus evacuated if it has not been already. If the object has already been evacuated from the referred-to location, the reference to that location is updated to point to the location to which the object has been evacuated. If the remembered set associated with the car containing the evacuated object's new location does not include an entry for the reference's location, it is updated to do so if the car containing the reference is younger than the car containing the evacuated object. Block 150 represents updating the reference and, if necessary, the remembered set.
As FIG. 8's blocks 112 and 114 indicate, this processing of collection-set remembered sets is performed initially only for entries that do not refer to locations in the oldest train. Those that do are processed only after all others have been, as blocks 152 and 154 indicate.
When this process has been completed, the collection set's memory space can be reclaimed, as block 164 indicates, since no remaining object is referred to from outside the collection set: any remaining collection-set object is unreachable. The collector then relinquishes control to the mutator.
FIGS. 12A–12J illustrate results of using the train algorithm. FIG. 12A represents a generation in which objects have been allocated in nine car sections. The oldest train has four cars, numbered 1.1 through 1.4. Car 1.1 has two objects, A and B. There is a reference to object B in the root set (which, as was explained above, includes live objects in the other generations). Object A is referred to by object L, which is in the third train's sole car section. In the generation's remembered sets 170, a reference in object L has therefore been recorded against car 1.1.
Processing always starts with the oldest train's earliest-added car, so the garbage collector refers to car 1.1's remembered set and finds that there is a reference from object L into the car being processed. It accordingly evacuates object A to the train that object L occupies. The object being evacuated is often placed in one of the selected train's existing cars, but we will assume for present purposes that there is not enough room. So the garbage collector evacuates object A into a new car section and updates appropriate data structures to identify it as the next car in the third train. FIG. 12B depicts is the result: a new car has been added to the third train, and object A is placed in it.
FIG. 12B also shows that object B has been evacuated to a new car outside the first train. This is because object B has an external reference, which, like the reference to object A, is a reference from outside the first train, and one goal of the processing is to form trains into which there are no further references. Note that, to maintain a reference to the same object, object L's reference to object A has had to be rewritten, and so have object B's reference to object A and the inter-generational pointer to object B. In the illustrated example, the garbage collector begins a new train for the car into which object B is evacuated, but this is not a necessary requirement of the train algorithm. That algorithm requires only that externally referenced objects be evacuated to a newer train.
Since car 1.1 no longer contains live objects, it can be reclaimed, as FIG. 12B also indicates. Also note that the remembered set for car 2.1 now includes the address of a reference in object A, whereas it did not before. As was stated before, remembered sets in the illustrated embodiment include only references from cars further back in the order than the one with which the remembered set is associated. The reason for this is that any other cars will already be reclaimed by the time the car associated with that remembered set is processed, so there is no reason to keep track of references from them.
The next step is to process the next car, the one whose index is 1.2. Conventionally, this would not occur until some collection cycle after the one during which car 1.1 is collected. For the sake of simplicity we will assume that the mutator has not changed any references into the generation in the interim.
FIG. 12B depicts car 1.2 as containing only a single object, object C, and that car's remembered set contains the address of an inter-car reference from object F. The garbage collector follows that reference to object C. Since this identifies object C as possibly reachable, the garbage collector evacuates it from car set 1.2, which is to be reclaimed. Specifically, the garbage collector removes object C to a new car section, section 1.5, which is linked to the train to which the referring object F's car belongs. Of course, object F's reference needs to be updated to object C's new location. FIG. 12C depicts the evacuation's result.
FIG. 12C also indicates that car set 1.2 has been reclaimed, and car 1.3 is next to be processed. The only address in car 1.3's remembered set is that of a reference in object G. Inspection of that reference reveals that it refers to object F. Object F may therefore be reachable, so it must be evacuated before car section 1.3 is reclaimed. On the other hand, there are no references to objects D and E, so they are clearly garbage. FIG. 12D depicts the result of reclaiming car 1.3's space after evacuating possibly reachable object F.
In the state that FIG. 12D depicts, car 1.4 is next to be processed, and its remembered set contains the addresses of references in objects K and C. Inspection of object K's reference reveals that it refers to object H, so object H must be evacuated. Inspection of the other remembered-set entry, the reference in object C, reveals that it refers to object G, so that object is evacuated, too. As FIG. 12E illustrates, object H must be added to the second train, to which its referring object K belongs. In this case there is room enough in car 2.2, which its referring object K occupies, so evacuation of object H does not require that object K's reference to object H be added to car 2.2's remembered set. Object G is evacuated to a new car in the same train, since that train is where referring object C resides. And the address of the reference in object G to object C is added to car 1.5's remembered set.
FIG. 12E shows that this processing has eliminated all references into the first train, and it is an important part of the train algorithm to test for this condition. That is, even though there are references into both of the train's cars, those cars' contents can be recognized as all garbage because there are no references into the train from outside of it. So all of the first train's cars are reclaimed.
The collector accordingly processes car 2.1 during the next collection cycle, and that car's remembered set indicates that there are two references outside the car that refer to objects within it. Those references are in object K, which is in the same train, and object A, which is not. Inspection of those references reveals that they refer to objects I and J, which are evacuated.
The result, depicted in FIG. 12F, is that the remembered sets for the cars in the second train reveal no inter-car references, and there are no inter-generational references into it, either. That train's car sections therefore contain only garbage, and their memory space can be reclaimed.
So car 3.1 is processed next. Its sole object, object L, is referred to inter-generationally as well as by a reference in the fourth train's object M. As FIG. 12G shows, object L is therefore evacuated to the fourth train. And the address of the reference in object L to object A is placed in the remembered set associated with car 3.2, in which object A resides.
The next car to be processed is car 3.2, whose remembered set includes the addresses of references into it from objects B and L. Inspection of the reference from object B reveals that it refers to object A, which must therefore be evacuated to the fifth train before car 3.2 can be reclaimed. Also, we assume that object A cannot fit in car section 5.1, so a new car 5.2 is added to that train, as FIG. 12H shows, and object A is placed in its car section. All referred-to objects in the third train having been evacuated, that (single-car) train can be reclaimed in its entirety.
A further observation needs to be made before we leave FIG. 12G. Car 3.2's remembered set additionally lists a reference in object L, so the garbage collector inspects that reference and finds that it points to the location previously occupied by object A. This brings up a feature of copying-collection techniques such as the typical train-algorithm implementation. When the garbage collector evacuates an object from a car section, it marks the location as having been evacuated and leaves the address of the object's new location. So, when the garbage collector traces the reference from object L, it finds that object A has been removed, and it accordingly copies the new location into object L as the new value of its reference to object A.
In the state that FIG. 12H illustrates, car 4.1 is the next to be processed. Inspection of the fourth train's remembered sets reveals no inter-train references into it, but the inter-generational scan (possibly performed with the: aid of FIG. 6's card tables) reveals inter-generational references into car 4.2. So the fourth train cannot be reclaimed yet. The garbage collector accordingly evacuates car 4.1's referred-to objects in the normal manner, with the result that FIG. 12I depicts.
In that state, the next car to be processed has only inter-generational references into it. So, although its referred-to objects must therefore be evacuated from the train, they cannot be placed into trains that contain references to them. Conventionally, such objects are evacuated to a train at the end of the train sequence. In the illustrated implementation, a new train is formed for this purpose, so the result of car 4.2's processing is the state that FIG. 12J depicts.
Processing continues in this same fashion. Of course, subsequent collection cycles will not in general proceed, as in the illustrated cycles, without any reference changes by the mutator and without any addition of further objects. But reflection reveals that the general approach just described still applies when such mutations occur.
Prior art discusses promoting objects from a younger into an older generation. Hudson and Moss, in their "Incremental Collection of Mature Objects," published in the Proceedings of the International Workshop on Memory management, 1992, Springer-Verlag, place each newly promoted object into an existing train that contains a reference to that object. If no such internal reference exists (an external reference or root exists), the new object is placed uniformly into a new or existing youngest train. Grarup and Seligmann, in their "Incremental Mature Garbage Collection using the Train Algorithm," disclosed at the European conference on Object-Oriented Programming 1995 Proceedings, similarly suggest that each newly promoted object be placed in an existing train that contains a reference to that object. If no such reference exists, again an external root, the new object is placed into a new or existing youngest train—referred to as a promotion train. In both of these cases the promotion train is the youngest train.
In both of these prior art cases the objects externally referenced are processed first and then the objects that are internally referenced. But, there is no order for the processing of roots within either of these two root sets. Further, promoted objects may be reachable by more than one internal or external root. The prior art does not address this occurrence and if present some randomly selected root will be processed first and the object is placed accordingly. However, this placement may be inefficient. The present invention addresses this issue of multiple roots.
One limitation of the prior art placement policy/algorithm is that those new objects placed into the youngest train may take up space long after they become unreachable. Objects placed in the youngest train must wait until the train holding them becomes the oldest train to be evacuated. This contributes to inefficient "floating" garbage. Another limitation of the prior art placement policy, as mentioned above, is that references are processed in a random order. Thus if there were several references to the same object but these references were in different trains, the train is determined by the first (randomly selected) reference processed. This random order selection may be inefficient. It may be too far away from collection thereby contributing to floating garbage, or it may be too close and not be given time to establish other connections or become unreachable.
There is a need to improve the efficiency of placement into a generation of newly promoted objects, especially objects that have multiple references from diverse trains in the older generation.

Better placement of objects promoted into a generation managed by the train algorithm


A programmable logic device unit, a non-volatile memory unit which stores data for programming the programmable logic device unit in a part of data storage area thereof and a control circuit which controls the non-volatile memory unit to allow the data stored in a part of the data storage area to be read at power-on time and supplied to the programmable logic device unit are integrally provided on a semiconductor chip. Based on the program data, the programmable logic device unit forms an interface for allowing the non-volatile memory unit to operate as at least one of a register, a flash memory, a random access memory, and a read-only memory.

The present invention relates to a semiconductor integrated circuit device incorporating a non-volatile memory unit and a programmable logic device unit.
Businesses that manufacture semiconductor chips in which system LSIs are provided around non-volatile memories such as NAND-type flash memories are spreading. However, the specification of a system LSI differs from one client to another, and the interface changes depending on the specification. Accordingly, a mask must be made for each product in its manufacturing process, increasing development cost and reducing versatility.
A technique that provides a flash memory unit on one semiconductor chip integrally with an FPGA unit, a CPU, a RAM, and the like and stores data for programming the FPGA unit in a SRAM static latch, an anti-fuse, a non-volatile memory cell, or the like is disclosed in Jpn. Pat. Appln. Publication No. 2003-218212.


Methods for improved stent retention on an expandable member during delivery are disclosed. Methods include fabricating delivery systems including a retention layer over the stent, the expandable member, or both for improving retention of the stent on the expandable member during delivery.

1. Field of the Invention
This invention relates to implantable medical devices, such as stents.
2. Description of the State of the Art
This invention relates to radially expandable endoprostheses, which are adapted to be implanted in a bodily lumen. An "endoprosthesis" corresponds to an artificial device that is placed inside the body. A "lumen" refers to a cavity of a tubular organ such as a blood vessel.
A stent is an example of such an endoprosthesis. Stents are generally cylindrically shaped devices, which function to hold open and sometimes expand a segment of a blood vessel or other anatomical lumen such as urinary tracts and bile ducts. Stents are often used in the treatment of atherosclerotic stenosis in blood vessels. "Stenosis" refers to a narrowing or constriction of the diameter of a bodily passage or orifice. In such treatments, stents reinforce body vessels and prevent restenosis following angioplasty in the vascular system. "Restenosis" refers to the reoccurrence of stenosis in a blood vessel or heart valve after it has been treated (as by balloon angioplasty, stenting, or valvuloplasty) with apparent success.
The treatment of a diseased site or lesion with a stent involves both delivery and deployment of the stent. "Delivery" refers to introducing and transporting the stent through a bodily lumen to a region, such as a lesion, in a vessel that requires treatment. "Deployment" corresponds to the expanding of the stent within the lumen at the treatment region. Delivery and deployment of a stent are accomplished by positioning the stent about one end of a catheter, inserting the end of the catheter through the skin into a bodily lumen, advancing the catheter in the bodily lumen to a desired treatment location, expanding the stent at the treatment location, and removing the catheter from the lumen.
In advancing a stent through a body vessel to a deployment site, the stent must be able to securely maintain its axial as well as rotational position on the delivery catheter without translocating proximally or distally, and especially without becoming separated from the catheter. Stents that are not properly secured or retained to the catheter may slip and either be lost or be deployed in the wrong location. The stent must be "crimped" in such a way as to minimize or prevent distortion of the stent and to thereby prevent abrasion and/or reduce trauma to the vessel walls.
Generally, stent crimping is the act of affixing the stent to the delivery catheter or delivery balloon so that it remains affixed to the catheter or balloon until the physician desires to deliver the stent at the treatment site. Current stent crimping technology is sophisticated. Examples of such technology which are known by one of ordinary skill in the art include a roll crimper; a collet crimper; and an iris or sliding-wedge crimper. To use a roll crimper, first the stent is slid loosely onto the balloon portion of the catheter. This assembly is placed between the plates of the roll crimper. With an automated roll crimper, the plates come together and apply a specified amount of force. They then move back and forth a set distance in a direction that is perpendicular to the catheter. The catheter rolls back and forth under this motion, and the diameter of the stent is reduced. The process can be broken down into more than one step, each with its own level of force, translational distance, and number of cycles. This process imparts a great deal of shear to the stent in a direction perpendicular to the catheter or catheter wall. Furthermore, as the stent is crimped, there is additional relative motion between the stent surface and the crimping plates.
The collet crimper is equally conceptually simple. A standard drill-chuck collet is equipped with several pie-piece-shaped jaws. These jaws move in a radial direction as an outer ring is turned. To use this crimper, a stent is loosely placed onto the balloon portion of a catheter and inserted in the center space between the jaws. Turning the outer ring causes the jaws to move inward. An issue with this device is determining or designing the crimping endpoint. One scheme is to engineer the jaws so that when they completely close, they touch and a center hole of a known diameter remains. Using this approach, turning the collet onto the collet stops crimps the stent to the known outer diameter. While this seems ideal, it can lead to problems. Stent struts have a tolerance on their thickness. Additionally, the process of folding non-compliant balloons is not exactly reproducible. Consequently, the collet crimper exerts a different amount of force on each stent in order to achieve the same final dimension. Unless this force, and the final crimped diameter, is carefully chosen, the variability of the stent and balloon dimensions can yield stent or balloon damage.
In the sliding wedge or iris crimper, adjacent pie-piece-shaped sections move inward and twist, much like the leaves in a camera aperture. This crimper can be engineered to have two different types of endpoints. It can stop at a final diameter, or it can apply a fixed force and allow the final diameter to float. From the discussion on the collet crimper, there are advantages in applying a fixed level of force as variability in strut and balloon dimension will not change the crimping force. The sliding wedges impart primarily normal forces. As the wedges slide over each other, they impart some tangential force. Lastly, the sliding wedge crimper presents a nearly cylindrical inner surface to the stent, even as it crimps. This means the crimping loads are distributed over the entire outer surface of the stent.
Current stent crimping methods were developed for all-metal stents. Stent metals, such as stainless steel, are durable and can take abuse. When crimping is too severe, it usually damages the underlying balloon, not the metal stent. But polymeric stents present different challenges. A polymer stent requires relatively wider struts than metal stents so as to provide suitable mechanical properties, such as radial strength. At the crimping stage, less space is provided between the struts which can result in less effective stent retention than a metallic stent, increasing the likelihood of detachment of the stent or premature deployment of the stent in the body. Moreover, the use of a high processing temperature during the crimping process to enhance stent retention may not be possible as a polymeric stent may have a glass transition temperature generally equivalent to the glass transition temperature of the balloon. Higher processing temperatures may cause the stent to lose some of its preferred mechanical properties.
The present invention includes methods of improving stent retention during delivery for polymeric stent. Such methods can are also applicable to metallic stents.


A magnetic recording medium includes a substrate, a magnetic layer including a FePt alloy having a L10 type structure, and a plurality of underlayers arranged between the substrate and the magnetic layer, wherein at least one of the plurality of underlayers includes TiO2.

1. Field of the Invention
The present invention relates to a magnetic recording medium and a magnetic storage apparatus.
2. Description of the Related Art
Recently, demands to increase storage capacities of HDDs (Hard Disk Drives) are increasing. As one means of satisfying such demands, a heat-assisted recording method and a microwave-assisted recording method have been proposed. The heat-assisted recording method performs recording with respect to a magnetic recording medium using a magnetic head mounted with a laser diode, by heating the magnetic recording medium by the magnetic head. The microwave-assisted recording method performs recording on the magnetic recording medium by applying a high-frequency magnetic field of 10 GHz or higher from the magnetic head.
The heat-assisted recording method can reduce the coercivity of the magnetic recording medium by heating the magnetic recording medium and enable use of a material having a high crystal magnetic anisotropy constant Ku (hereinafter also referred to as a "high-Ku material") for a magnetic layer of the magnetic recording medium. For this reason, the magnetic grain size of the magnetic layer can be reduced while maintaining thermal stability, and a surface recording density on the order of 1 Tbits/inch2 can be achieved.
On the other hand, the microwave-assisted recording method can perform the recording with respect to the magnetic recording medium with a recording magnetic field lower than or equal to the coercivity of the magnetic recording medium, by the assistance of the high-frequency magnetic field generated from an STO (Spin Torque Oscillator) mounted on the magnetic head. For this reason, similarly as in the case of the heat-assisted recording method, the microwave-assisted recording method can use a high-Ku material for the magnetic layer of the magnetic recording medium.
Ordered alloys, such as L10 type FePt alloys, L10 type CoPt alloys, L11 type CoPt alloys, and the like, have been proposed for the high-Ku material. In addition, in order to separate crystal grains of the ordered alloy, the magnetic layer is added with a grain boundary material, such as an oxide including SiO2, TiO2, or the like, or C, BN, or the like. By employing a granular structure in which the magnetic crystal grains are separated at the grain boundary, a high medium SNR (Signal-to-Noise Ratio) can be achieved.
When the L10 type FePt alloy described above is used for the magnetic layer, a (001) orientation in which the c-axis is perpendicular to the layer surface is desirable in order to achieve a high perpendicular magnetic anisotropy. It is known that the orientation of the L10 type FePt alloy is controllable by an underlayer.
For example, Japanese Laid-Open Patent Publication No. 11-353648 proposes forming the L10 type FePt alloy on an underlayer that is made of MgO, NiO, or the like and is controlled to have a (100) face parallel to the substrate surface, in order to obtain the (001) orientation of the L10 type FePt alloy.
In addition, Japanese Laid-Open Patent Publication No. 2009-146558 and U.S. Pat. No. 7,829,208 propose forming the L10 type FePt magnetic layer on an underlayer that is made of ZrN, TaN, CrN, or the like and has an NaCl type structure, in order to obtain satisfactory (001) orientation of the L10 type FePt magnetic layer.
Furthermore, Akira Yano et al., "FePt fct Phase Ordered Alloy Thin Film Prepared by 30-s Annealing With Fe—O Under-Layer", IEEE Trans. Magn., Vol. 41, No. 10, pp. 3211-3213, October 2005, Yoshiko Tsuji et al., "Structure and magnetic property of c-axis oriented L10-FePt nanoparticles on TiN/a-Si underlayers", J. Vac. Sci. Technol. B25(6), pp. 1892-1895, November/December 2007, and En Yang et al., "Epitaxial Growth of L10-FePt Granular Thin Films on TiC/RuAl Underlayers", IEEE Trans. Magn. Vol. 47, No. 10, pp. 4077-4079, October 2011 propose forming the L10 type FePt magnetic layer on a FeO underlayer, a TiN underlayer, and a TiC underlayer respectively having the NaCl type structure, in order to obtain the (001) orientation of the L10 type FePt magnetic layer.
Recently, there are demands to improve the medium SNR of the magnetic recording medium. However, although the perpendicular magnetic anisotropy can be improved by making the L10 type FePt alloy included in the magnetic layer have the (001) orientation, a sufficient improvement of the medium SNR may be difficult to achieve.

Magnetic recording medium and magnetic storage apparatus


The disclosure generally relates to a method and apparatus for a fiberscope. In one embodiment, the disclosure relates to a chemical imaging fiberscope for imaging and collecting optical spectra from a sample having at least one illumination fiber for transmitting light from a first an a second light source to a distal end of a fiberscope; a dichroic mirror disposed at said distal end of the fiberscope such that light from said first light source passes substantially straight through said mirror and light of a predetermined wavelength from said second light source is substantially reflected by said mirror toward said sample to thereby illuminate said sample; and at least one collection fiber for receiving light from said illuminated sample and transmitting the received light to an optical device.

Chemical imaging combines optical spectroscopy and digital imaging for the molecular-specific analysis of materials. Raman, visible, near infrared (VIS/NIR) and Fluorescence chemical imaging have traditionally been performed in laboratory settings using research-grade light microscope technology as the image gathering platform. However, chemical imaging is applicable to in situ industrial process monitoring and in vivo clinical analysis. The application of chemical imaging outside the research laboratory has been limited by the lack of availability of stable imaging platforms that are compatible with the physical demands of industrial process monitoring and clinical environments. Both industrial and clinical settings often require compact, lightweight instrumentation suitable for the examination of remote areas that are inaccessible to conventional chemical imaging instrumentation and involve harsh chemicals in hostile areas. In addition, for in vivo cardio-vascular clinical applications, the presence of blood and bodily fluids limits the viewing, identification and ability to perform in vivo optical measurements of suspect areas.
Raman spectroscopy is one of the analytical technique that is broadly applicable and can be used for chemical imaging. Among its many desirable characteristics, Raman spectroscopy is compatible with samples in aqueous environments and can be performed on samples undergoing little or no sample preparation. The technique is particularly attractive for remote analysis via the use of optical fibers. By employing optical fibers for light delivery and collection the light source and light detector can be physically separated from the sample. This remote attribute is particularly valuable in sensing and analysis of samples found in industrial process environments and living subjects.
In a typical fiber-optic based Raman analysis configuration, one or more illumination fiber-optics deliver light from a light source (typically a laser) through a laser bandpass optical filter and onto a sample. The laser bandpass filter allows only the laser wavelength to pass while rejecting all other wavelengths. This purpose of the bandpass filter is to eliminate undesired wavelengths of light from reaching the sample. Upon interaction with the sample, much of the laser light is scattered at the same wavelength as the laser. However, a small portion of the scattered light (1 in 1 million scattered photons on average) is scattered at wavelengths different from the laser wavelength. This phenomenon is known as Raman scattering. The collective wavelengths generated from Raman scattering from a sample are unique to the chemistry of that sample. The unique wavelengths provide a fingerprint for the material and are graphically represented in the form of a spectrum. The Raman scattered light generated by the laser/sample interaction is then gathered using collection optics which directs the light through laser rejection filter which eliminates the laser light, allowing only Raman light to be transmitted. The transmitted light is then coupled to a detection system via one or more collection fiber-optics.
Previously described Raman fiber optic probe devices have several limitations. First, current fiber-optic-based Raman probes are sensitive to environmental variability. These devices often fail to function properly when the probe is subjected to hot, humid and/or corrosive environments. Several fundamental differences from current devices have been incorporated into the chemical imaging fiberscope design described here that address the environmental sensitivity issue. First, an outer jacket (or housing) that is mechanically rugged and resistant to varying temperatures and high humidity has been incorporated into the fiberscope design. Second, an optically transparent window that withstands harsh operating environment has been built into the probe at the fiberscope/sample interface. Normally, incorporation of a window into a probe would introduce a significant engineering problem. As emitted illumination light passes through the window and onto the sample, a portion of this light is back reflected by the window's inner and outer surfaces. In the prior art, this undesired back reflected light is inadvertently introduced into the collection fibers along with the desired Raman scattered light. The back reflected light corrupts the quality of the analysis. This problem is addressed in the current design by careful engineering of the aperture of the collection bundle taking into account the numerical apertures (NA) associated with the collection bundle fibers and collection lenses.
Previous probe designs are also inadequate because of the environmental sensitivity of the spectral filters that are employed in the devices. The chemical imaging fiberscope design of the current disclosure relies on spectral filter technologies that are remarkably immune to temperature and humidity. Past spectral filters have traditionally been fabricated using conventional thin film dielectric filter technology which are susceptible to temperature and humidity induced degradation in the filter spectral performance. The spectral filters described in the present disclosure employ highly uniform, metal oxide thin film coating material such as SiO2 which exhibits a temperature dependent spectral band shift coefficient an order of magnitude less than conventional filter materials. The improved quality and temperature drift performance of metal oxide filters imparts dramatically improved environmental stability and improved Raman performance under extreme conditions of temperature and humidity.
Another limitation of current probe technologies is that none combine the three basic functions of the chemical imaging fiberscope: (1) video inspection; (2) spectral analysis; and (3) chemical image analysis in an integrated, compact device.
Raman chemical imaging integrates the molecular analysis capabilities of Raman spectroscopy with image acquisition through the use of electronically tunable imaging spectrometers. In Raman chemical imaging, scattered Raman light is shifted in wavelength from the wavelength of the illuminating light. For example, Raman illumination at 532 nm can excite molecular vibrations in the sample at for example, 4000 cm−1 to produce scatter Raman light at lower and higher wavelengths of 439.3 nm and 647.5 nm, respectively. The Raman wavelength can be in the range of −4000–4000 cm−1. This produced Raman features 4000 cm−1 above the illuminating wavelength. Several imaging spectrometers have been employed for Raman chemical imaging, including acousto-optical tunable filters (AOTFs) and liquid crystal tunable filters (LCTFs). For Raman imaging, LCTFs are clearly the instrument of choice based on the following demonstrated figures of merit: spatial resolving power (250 nm); spectral resolving power (<0.1 cm−1); large clear aperture (20 mm); and free spectral range (0–4000 cm−1). LCTF's can also be designed by those skilled in the art to operate over different ranges of detection wavelengths that depend on the application from, for example, 400–720 nm, 650–1100 nm, 850–1800 nm or 1200–2400 nm. AOTFs and LCTFs are competitive technologies. AOTFs suffer from image artifacts and instability when subjected to temperature changes.
Under normal Raman imaging operation, LCTFs allow Raman images of samples to be recorded at discrete wavelengths (energies). A spectrum is generated corresponding to thousands of spatial locations at the sample surface by tuning the LCTF over a range of wavelengths and collecting images systemically. Contract is generated in the images based on the relative amounts of Raman scatter or other optical phenomena such as luminescence that is generated by the different species located throughout the sample. Since a spectrum is generated for each pixel location, chemometric analysis tools such as Cosine Correlation Analysis (CCA), Principle Component Analysis (PCA) and Multivariate Curve Resolution (MCR) are applied to the image data to extract pertinent information.
Chemical imaging can be performed not only in a scattering mode at high resolution as done for Raman chemical imaging using laser illumination, but it can also be conducted for broadband incident illumination (wavelength>10 cm−1) at corresponding reduced spectral resolution (wavelength>10 cm−1). This broadband illumination and reduced resolution spectroscopy can be done in the UV wavelength (200–400 nm), VIS wavelength (400–780 nm) and NIR wavelength (780–2500 nm) regions to measure the optical absorption and emission from the sample. Performing such absorption or emission measurements using a fiberscope requires addressing many of the same problems as encountered in performing Raman imaging. The ability to perform combinations of these optical measurements and chemical imaging in the same fiberscope system is also an advantage in that enabling different chemical imaging technologies in one platform provides valuable complementary information.
One problem in performing chemical analysis and chemical imaging in the human body, such as in for example, in the cardio-vascular system or body cavities during, for example, endoscopic surgery, is the occurrence of significant amounts of blood and water at the sample site which both scatters and absorb light in certain wavelength ranges. Further, the positioning of a fiberscope probe to perform an in vivo optical analysis requires accurate steering and viewing thru these body fluids so as to define regions of interest and accurately position the optical probe at the region to be sampled. Viewing more than a few millimeters through blood requires observation at NIR wavelengths. However, such NIR wavelengths are poorly suited for performing Raman scattering or fluorescence measurements.
For example, identification and characterization of vulnerable plaque in the cardio-vascular system is critically related to Cardio vascular disease which is a leading cause of deaths in the United Stated. The in vivo identification and characterization of plaques in the cardio vascular system requires locating the suspect regions and positioning a sampling probe to analyze these regions. Other current methods for characterizing vulnerable plaque such as Intra Vascular UltraSound (IVUS) and thermometry (e.g., Volcano Therapuetics, Inc.) map out some physical properties of the arterial walls to suggest likely areas of plaques, but are not chemically specific and cannot provide any detailed analytical information regarding the chemical state or molecular composition of these target areas or plaques. Optical imaging to position a chemical probe in vivo is desirable but problematic and limited due to the scattering and absorption properties of blood. While certain optical wavelengths in the NIR are known to be more favorable than others for in vivo viewing of the cardiovascular system, these wavelengths are not well-suitable for performing highly specific chemical analysis. For example, the Raman scattering cross sections at longer wavelengths (e.g., NIR) are reduced from VIS wavelength excitation by the fourth power of their respective frequencies. The low cost, high sensitivity Si charge-coupled detectors ("CCD") used for Raman Chemical imaging also have reduced sensitivity for longer wavelength Raman scattered peaks thereby making it difficult to detect the very important CH-bond vibrational region.
Thus, there is a need for an apparatus and method to enable long range viewing, steering and targeting which is optimal in the NIR as well as subsequent and/or simultaneous chemical imaging of the target area which is optimal in the visible range. This invention addresses that need.


A contact image sensor unit includes: a light source (10) illuminating an original; a rod-like light guide (11) guiding light from the light source to the original; an imaging element (12) forming reflected light from the original on a plurality of photoelectric conversion elements; a sensor substrate (14) on which the plurality of photoelectric conversion elements are mounted; a frame (15) to which they are attached and which has a positioning part (200) for attaching the light guide (11) thereto; and a supporting member (16) which attachably/detachably supports the light guide (11) and is attachably/detachably attached to the positioning part (200). Since the light guide (11) can be attached to the frame (15) without using an adhesive, the deformation of the light guide (11), the warpage of the contact image sensor unit and so on can be prevented.

In the image reading apparatus such as an image scanner, copying machine and so on, a contact image sensor unit which is brought into close contact with the original to read the original at the same magnification has been conventionally used as the image sensor optically reading image information on the original and converting the information into electric signals.
The contact image sensor unit is used while being attached below a transparent original supporting body supporting the original in the image reading apparatus. There are two main methods of attaching the contact image sensor unit in the image reading apparatus as follows.
(1) A flatbed-type in which reading is performed by moving the image sensor unit with the original fixed on the original supporting body of the image reading apparatus.
(2) A sheetfeed-type in which reading is performed by moving the original on the original supporting body with the image sensor unit fixed to the image reading apparatus.
These examples are disclosed in Patent Literature 1.
It is known that in a configuration example of the conventional contact image sensor unit used for them, an illumination device composed of a light source using an LED for illuminating the original and a light guide is attached to a frame. This illumination device is composed of a light guide which takes in emitted light from the light source and emits the light so that the illumination amount becomes almost uniform over the length of one line of an original reading part. Further, the frame also includes a sensor substrate on which a sensor array formed by arranging a plurality of photoelectric conversion elements including a plurality of light receiving parts performing photoelectric conversion of an optical image of the original into electric signals in lines is mounted, and a lens array forming an optical image of the original on the sensor array. Further, a connector electrically connecting the sensor array to an external device is attached to the sensor substrate.
The conventional contact image sensor unit is attached below a transparent glass being the original supporting body in the above-described type (1). On the other hand, a transparent glass being the original supporting body is attached on the contact image sensor unit in the above-described type (2).
Here, when the light guide is fixed to the frame of the contact image sensor unit with an adhesive or the like, there are following problems. Specifically, the materials of the frame and the light guide are different, thus possibly causing poor conditions such as the deformation of the light guide caused by the thermal expansion and/or contraction due to a change in environmental temperature, and the warpage of the contact image sensor unit and the like.
In Patent Literature 2, to cope with the thermal expansion difference and thermal contraction difference generated between the frame and the light guide constituting the illumination device, an image sensor as illustrated in FIG. 14 is proposed. An image sensor (a contact image sensor unit) 400 illustrated in FIG. 14 irradiates an original with light from a line illumination device to image reflection light from the irradiated original on a light receiving element array (photoelectric conversion element) 402 by a lens array (imaging element) 401 and then reads the image. Further, the line illumination device (illumination device) is composed of a light emitting element (light source) and a light guide 403. The light guide 403 is structured to be pressed against a frame 406 by a claw part 405 provided at the tip of an elastic holding part 404. Therefore, even when there is a thermal expansion difference or thermal contraction difference between the line illumination device and the frame 406, there is no stress occurring between them, resulting in no poor condition such as warpage or the like on the image sensor 400. Further, it is also disclosed that since the line illumination device is fixed to the frame 406 of the image sensor 400 by the elastic holding part 404, the line illumination device can be easily detached.
However, in this conventional technique, it is difficult to integrally mold the frame 406 and the elastic holding part 404 which needs to be made of a material having elastic characteristics different from that of the frame 406 and have a complicated shape in consideration of the shape and the detachability of the light guide 403 and the like.
Furthermore, there is a problem in terms of production management of the contact image sensor unit production as follows.
There is a demand to make the outside dimensions of frames uniform in order to commonalize the assembly work and related peripheral components. However, there are variations in the specifications, shape, attachment position, direction of emitted light and so on of the light guide used in the contact image sensor unit. For example, is necessary to prepare light guides in various shapes to cope with the illumination angle or direction due to the difference in distance between the contact image sensor and the original, and to cope with various modifications in the attachment position and angle of the light guide to the frame.
Accordingly, in the production of the contact image sensor unit, it is necessary to prepare many kinds of individual frames to cope with the difference in shape, attachment position and angle of the light guide, requiring labor in production management. Further, FIG. 12 of the above-described Patent Literature 2 discloses a CIS unit in which two line illumination devices are arranged to be substantially symmetric about a lens array located at the middle. The two structures of the light guides and the cases housing the light guides used in the line illumination devices are the same. Further, in Patent Literature 1, the two right and left light guides are configured to be different in irradiation angle and position to the lens array at the middle in order to increase the illumination depth, thereby increasing the quality of the image sensor unit in terms of the illumination depth and the illumination amount to the original.

Contact image sensor unit including a detachable light guide supporting member and image reading apparatus using the same


A microparticle dispersion liquid manufacturing apparatus 10 includes a controller 11, a light source 12, an irradiation optical system 13, and a container 14. A solid object 1 is contained in and a solvent 2 is injected into an interior of the container 14 to enable attainment of a state where the solid object 1 is in contact with the solvent 2. The light source 12 repeatedly outputs pulsed light. By repeatedly irradiating the solvent 2 with the pulsed light from the light source 12, expansion and contraction of the solvent 2 is made to occur repeatedly at the irradiated portion, thereby generating a pressure wave in the solvent 2, and the pressure wave is made to act on the solid object 1 to finely pulverize the solid object 1 and thereby manufacture a microparticle dispersion liquid in which microparticles are dispersed in the solvent. A microparticle dispersion liquid manufacturing method and manufacturing apparatus are thereby realized by which both suppression of impurity formation and an increase in efficiency of microparticle formation can be achieved readily.

In the recent development of new medical drugs, combinatorial chemistry methods have been adopted in synthesizing candidate compounds. Combinatorial chemistry is the art of adopting combinations to synthesize a wide variety of compounds in a short time at one time. Compounds obtained by this method have a solubility problem in many cases. That is, in many cases, even if a compound is found to have excellent physiological activity in itself, if the compound has a property of being difficult to dissolve in water, development of the compound is abandoned. Even with compounds obtained by extraction from natural products, various organic syntheses are carried out and structural optimization is performed to improve solubility. Some medical drugs already on the market are also low in solubility. With such drugs, a medicament absorption amount varies within an individual patient and varies among individuals, and this places a large burden in terms of control of levels in blood, etc., on both a physician using a drug and a patient on whom the drug is used.
Microparticle formulations have received attention as a solution to the above problems. With a microparticle formulation, poorly-soluble medicament particles that are made no more than a micrometer in size are dispersed in water with stability. By using a microparticle formulation, a medicament can be increased in absorption rate and amount in a living body. Reduction in variation of absorption amount within an individual patient and among individuals and increase in effective availability with respect to a dose can also be anticipated. Inventions of methods for manufacturing such microparticle formulations are disclosed in Patent Documents 1 and 2.
With the invention disclosed in Patent Document 1, in order to finely pulverize a solid object, which is suspended in a solvent of a treatment target liquid without being dissolved, and thereby manufacture microparticles of the solid object, the treatment target liquid is irradiated with light of a predetermined wavelength, which is longer than an absorption band of the solid object, is in an absorption band of the solvent, and is absorbed by the solvent, to finely pulverize the solid object, and an irradiation intensity of the light irradiated on the treatment target liquid is made lower than an irradiation light intensity at which two-photon absorption occurs in the solid object.
With the invention disclosed in Patent Document 2, a solid object is finely pulverized by injecting water into an interior of a container in which the solid object is fixed to an inner wall and irradiating the solid object fixed to the inner wall of the container with light. In irradiation with the light, the light is irradiated from outside a region of the inner wall of the container at which the solid object is fixed to make the irradiated light propagate in the order of the container, the solid object, and the water so that microparticles can be formed at a fixed efficiency without lowering of efficiency of microparticle formation even in a state where the water contains a high concentration of microparticles.

Fine-particle dispersion liquid manufacturing method and fine-particle dispersion liquid manufacturing apparatus


According to one embodiment, a cargo handling apparatus includes a first mechanism, a second mechanism, a holding unit, a third mechanism, a fourth mechanism and a conveyor. The first mechanism is movable in a first direction. The second mechanism is connected to the first mechanism and is movable on a first horizontal plane intersecting the first direction. The holding unit is connected to the second mechanism and holds an object to be picked up. The third mechanism is arranged below the first mechanism, the second mechanism and the holding unit, and is movable in the first direction. The fourth mechanism is connected to the third mechanism and is movable on a second horizontal plane opposed to the first horizontal plane. The conveyor is connected to the fourth mechanism, and loads and conveys the object held by the holding unit.

Due to the globalization of supply chains and the aging of the working population, there has been a trend of shortages in the labor force for handling the increased volume of physical distribution. Therefore, Cartesian robots and articulated-arm robots have been popularized to achieve high-speed and effective cargo handling operations, such as picking of goods.