used to provide mutual exclusion of data structures; most notable of these is compare-and-swap (CAS). CAS can be used to achieve wait-free mutual exclusion for any shared data structure by creating a linked list where each node represents the desired operation to be performed. CAS is then used to change the pointers in the linked list during the insertion of a new node. Only one process can be successful in its CAS; all other processes attempting to add a node at the same time will have to try again. Each process can then keep a local copy of the data structure, and upon traversing the linked list, can perform each operation from the list on its local copy. Software solutions In addition to hardware-supported solutions, some software solutions exist that use busy waiting to achieve mutual exclusion. Examples include: Dekker's algorithm Peterson's algorithm Lamport's bakery algorithm Szymański's algorithm Taubenfeld's black-white bakery algorithm Maekawa's algorithm These algorithms do not work if out-of-order execution is used on the platform that executes them. Programmers have to specify strict ordering on the memory operations within a thread. It is often preferable to use synchronization facilities provided by an operating system's multithreading library, which will take advantage of hardware solutions if possible but will use software solutions if no hardware solutions exist. For example, when the operating system's lock library is used and a thread tries to acquire an already acquired lock, the operating system could suspend the thread using a context switch and swap it out with another thread that is ready to be run, or could put that processor into a low power state if there is no other thread that can be run. Therefore, most modern mutual exclusion methods attempt to reduce latency and busy-waits by using queuing and context switches. However, if the time that is spent suspending a thread and then restoring it can be proven to be always more than the time that must be waited for a thread to become ready to run after being blocked in a particular situation, then spinlocks are an acceptable solution (for that situation only). Bound on the mutual exclusion problem One binary test&set register is sufficient to provide the deadlock-free solution to the mutual exclusion problem. But a solution built with a test&set register can possibly lead to the starvation of some processes which become caught in the trying section. In fact,