text: /**********************************************************************
   * $Id$
   *
   * Name:     cpl_virtualmem.h
   * Project:  CPL - Common Portability Library
   * Purpose:  Virtual memory
   * Author:   Even Rouault, <even dot rouault at mines dash paris dot org>
   *
   **********************************************************************
   * Copyright (c) 2014, Even Rouault <even dot rouault at mines-paris dot org>
   *
   * Permission is hereby granted, free of charge, to any person obtaining a
   * copy of this software and associated documentation files (the "Software"),
   * to deal in the Software without restriction, including without limitation
   * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   * and/or sell copies of the Software, and to permit persons to whom the
   * Software is furnished to do so, subject to the following conditions:
   * 
   * The above copyright notice and this permission notice shall be included
   * in all copies or substantial portions of the Software.
   * 
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
   * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
   * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER 
   * DEALINGS IN THE SOFTWARE.
   ****************************************************************************/
  
  #ifndef _CPL_VIRTUAL_MEM_INCLUDED
  #define _CPL_VIRTUAL_MEM_INCLUDED
  
  #include "cpl_port.h"
  #include "cpl_vsi.h"
  
  CPL_C_START
  
  /**
   * \file cpl_virtualmem.h
   *
   * Virtual memory management.
   *
   * This file provides mechanism to define virtual memory mappings, whose content
   * is allocated transparently and filled on-the-fly. Those virtual memory mappings
   * can be much larger than the available RAM, but only parts of the virtual
   * memory mapping, in the limit of the allowed the cache size, will actually be
   * physically allocated.
   *
   * This exploits low-level mechanisms of the operating system (virtual memory
   * allocation, page protection and handler of virtual memory exceptions).
   *
   * It is also possible to create a virtual memory mapping from a file or part
   * of a file.
   *
   * The current implementation is Linux only.
   */
  
  /** Opaque type that represents a virtual memory mapping. */
  typedef struct CPLVirtualMem CPLVirtualMem;
  
  /** Callback triggered when a still unmapped page of virtual memory is accessed.
    * The callback has the responsibility of filling the page with relevant values
    *
    * @param ctxt virtual memory handle.
    * @param nOffset offset of the page in the memory mapping.
    * @param pPageToFill address of the page to fill. Note that the address might
    *                    be a temporary location, and not at CPLVirtualMemGetAddr() + nOffset.
    * @param nToFill number of bytes of the page.
    * @param pUserData user data that was passed to CPLVirtualMemNew().
    */
  typedef void (*CPLVirtualMemCachePageCbk)(CPLVirtualMem* ctxt,
                                      size_t nOffset,
                                      void* pPageToFill,
                                      size_t nToFill,
                                      void* pUserData);
  
  /** Callback triggered when a dirty mapped page is going to be freed.
    * (saturation of cache, or termination of the virtual memory mapping).
    *
    * @param ctxt virtual memory handle.
    * @param nOffset offset of the page in the memory mapping.
    * @param pPageToBeEvicted address of the page that will be flushed. Note that the address might
    *                    be a temporary location, and not at CPLVirtualMemGetAddr() + nOffset.
    * @param nToBeEvicted number of bytes of the page.
    * @param pUserData user data that was passed to CPLVirtualMemNew().
    */
  typedef void (*CPLVirtualMemUnCachePageCbk)(CPLVirtualMem* ctxt,
                                        size_t nOffset,
                                        const void* pPageToBeEvicted,
                                        size_t nToBeEvicted,
                                        void* pUserData);
  
  /** Callback triggered when a virtual memory mapping is destroyed.
    * @param pUserData user data that was passed to CPLVirtualMemNew().
   */
  typedef void (*CPLVirtualMemFreeUserData)(void* pUserData);
  
  /** Access mode of a virtual memory mapping. */
  typedef enum
  {
      /*! The mapping is meant at being read-only, but writes will not be prevented.
          Note that any content written will be lost. */
      VIRTUALMEM_READONLY,
      /*! The mapping is meant at being read-only, and this will be enforced 
          through the operating system page protection mechanism. */
      VIRTUALMEM_READONLY_ENFORCED,
      /*! The mapping is meant at being read-write, and modified pages can be saved
          thanks to the pfnUnCachePage callback */
      VIRTUALMEM_READWRITE
  } CPLVirtualMemAccessMode;
  
  
  /** Return the size of a page of virtual memory.
   *
   * @return the page size.
   *
   * @since GDAL 1.11
   */
  size_t CPL_DLL CPLGetPageSize(void);
  
  /** Create a new virtual memory mapping.
   *
   * This will reserve an area of virtual memory of size nSize, whose size
   * might be potentially much larger than the physical memory available. Initially,
   * no physical memory will be allocated. As soon as memory pages will be accessed,
   * they will be allocated transparently and filled with the pfnCachePage callback.
   * When the allowed cache size is reached, the least recently used pages will
   * be unallocated.
   *
   * On Linux AMD64 platforms, the maximum value for nSize is 128 TB.
   * On Linux x86 platforms, the maximum value for nSize is 2 GB.
   *
   * Only supported on Linux for now.
   *
   * Note that on Linux, this function will install a SIGSEGV handler. The
   * original handler will be restored by CPLVirtualMemManagerTerminate().
   *
   * @param nSize size in bytes of the virtual memory mapping.
   * @param nCacheSize   size in bytes of the maximum memory that will be really
   *                     allocated (must ideally fit into RAM).
   * @param nPageSizeHint hint for the page size. Must be a multiple of the
   *                      system page size, returned by CPLGetPageSize().
   *                      Minimum value is generally 4096. Might be set to 0 to
   *                      let the function determine a default page size.
   * @param bSingleThreadUsage set to TRUE if there will be no concurrent threads
   *                           that will access the virtual memory mapping. This can
   *                           optimize performance a bit.
   * @param eAccessMode permission to use for the virtual memory mapping.
   * @param pfnCachePage callback triggered when a still unmapped page of virtual
   *                     memory is accessed. The callback has the responsibility
   *                     of filling the page with relevant values.
   * @param pfnUnCachePage callback triggered when a dirty mapped page is going to
   *                       be freed (saturation of cache, or termination of the
   *                       virtual memory mapping). Might be NULL.
   * @param pfnFreeUserData callback that can be used to free pCbkUserData. Might be
   *                        NULL
   * @param pCbkUserData user data passed to pfnCachePage and pfnUnCachePage.
   *
   * @return a virtual memory object that must be freed by CPLVirtualMemFree(),
   *         or NULL in case of failure.
   *
   * @since GDAL 1.11
   */
  
  CPLVirtualMem CPL_DLL *CPLVirtualMemNew(size_t nSize,
                                          size_t nCacheSize,
                                          size_t nPageSizeHint,
                                          int bSingleThreadUsage,
                                          CPLVirtualMemAccessMode eAccessMode,
                                          CPLVirtualMemCachePageCbk pfnCachePage,
                                          CPLVirtualMemUnCachePageCbk pfnUnCachePage,
                                          CPLVirtualMemFreeUserData pfnFreeUserData,
                                          void *pCbkUserData);
  
  
  /** Return if virtual memory mapping of a file is available.
   *
   * @return TRUE if virtual memory mapping of a file is available.
   * @since GDAL 1.11
   */
  int CPL_DLL CPLIsVirtualMemFileMapAvailable(void);
  
  /** Create a new virtual memory mapping from a file.
   *
   * The file must be a "real" file recognized by the operating system, and not
   * a VSI extended virtual file.
   *
   * In VIRTUALMEM_READWRITE mode, updates to the memory mapping will be written
   * in the file.
   *
   * On Linux AMD64 platforms, the maximum value for nLength is 128 TB.
   * On Linux x86 platforms, the maximum value for nLength is 2 GB.
   *
   * Only supported on Linux for now.
   *
   * @param  fp       Virtual file handle.
   * @param  nOffset  Offset in the file to start the mapping from.
   * @param  nLength  Length of the portion of the file to map into memory.
   * @param eAccessMode Permission to use for the virtual memory mapping. This must
   *                    be consistent with how the file has been opened.
   * @param pfnFreeUserData callback that is called when the object is destroyed.
   * @param pCbkUserData user data passed to pfnFreeUserData.
   * @return a virtual memory object that must be freed by CPLVirtualMemFree(),
   *         or NULL in case of failure.
   *
   * @since GDAL 1.11
   */
  CPLVirtualMem CPL_DLL *CPLVirtualMemFileMapNew( VSILFILE* fp,
                                                  vsi_l_offset nOffset,
                                                  vsi_l_offset nLength,
                                                  CPLVirtualMemAccessMode eAccessMode,
                                                  CPLVirtualMemFreeUserData pfnFreeUserData,
                                                  void *pCbkUserData );
  
  /** Create a new virtual memory mapping derived from an other virtual memory
   *  mapping.
   *
   * This may be useful in case of creating mapping for pixel interleaved data.
   *
   * The new mapping takes a reference on the base mapping.
   *
   * @param pVMemBase Base virtual memory mapping
   * @param nOffset   Offset in the base virtual memory mapping from which to start
   *                  the new mapping.
   * @param nSize     Size of the base virtual memory mapping to expose in the
   *                  the new mapping.
   * @param pfnFreeUserData callback that is called when the object is destroyed.
   * @param pCbkUserData user data passed to pfnFreeUserData.
   * @return a virtual memory object that must be freed by CPLVirtualMemFree(),
   *         or NULL in case of failure.
   *
   * @since GDAL 1.11
   */
  CPLVirtualMem CPL_DLL *CPLVirtualMemDerivedNew(CPLVirtualMem* pVMemBase,
                                                 vsi_l_offset nOffset,
                                                 vsi_l_offset nSize,
                                                 CPLVirtualMemFreeUserData pfnFreeUserData,
                                                 void *pCbkUserData);
  
  /** Free a virtual memory mapping.
   *
   * The pointer returned by CPLVirtualMemGetAddr() will no longer be valid.
   * If the virtual memory mapping was created with read/write permissions and that
   * they are dirty (i.e. modified) pages, they will be flushed through the
   * pfnUnCachePage callback before being freed.
   *
   * @param ctxt context returned by CPLVirtualMemNew().
   *
   * @since GDAL 1.11
   */
  void CPL_DLL CPLVirtualMemFree(CPLVirtualMem* ctxt);
  
  /** Return the pointer to the start of a virtual memory mapping.
   *
   * The bytes in the range [p:p+CPLVirtualMemGetSize()-1] where p is the pointer
   * returned by this function will be valid, until CPLVirtualMemFree() is called.
   *
   * Note that if a range of bytes used as an argument of a system call
   * (such as read() or write()) contains pages that have not been "realized", the
   * system call will fail with EFAULT. CPLVirtualMemPin() can be used to work
   * around this issue.
   *
   * @param ctxt context returned by CPLVirtualMemNew().
   * @return the pointer to the start of a virtual memory mapping.
   *
   * @since GDAL 1.11
   */
  void CPL_DLL *CPLVirtualMemGetAddr(CPLVirtualMem* ctxt);
  
  /** Return the size of the virtual memory mapping.
   *
   * @param ctxt context returned by CPLVirtualMemNew().
   * @return the size of the virtual memory mapping.
   *
   * @since GDAL 1.11
   */
  size_t CPL_DLL CPLVirtualMemGetSize(CPLVirtualMem* ctxt);
  
  /** Return if the virtal memory mapping is a direct file mapping.
   *
   * @param ctxt context returned by CPLVirtualMemNew().
   * @return TRUE if the virtal memory mapping is a direct file mapping.
   *
   * @since GDAL 1.11
   */
  int CPL_DLL CPLVirtualMemIsFileMapping(CPLVirtualMem* ctxt);
  
  /** Return the access mode of the virtual memory mapping.
   *
   * @param ctxt context returned by CPLVirtualMemNew().
   * @return the access mode of the virtual memory mapping.
   *
   * @since GDAL 1.11
   */
  CPLVirtualMemAccessMode CPL_DLL CPLVirtualMemGetAccessMode(CPLVirtualMem* ctxt);
  
  /** Return the page size associated to a virtual memory mapping.
   *
   * The value returned will be at least CPLGetPageSize(), but potentially
   * larger.
   *
   * @param ctxt context returned by CPLVirtualMemNew().
   * @return the page size
   *
   * @since GDAL 1.11
   */
  size_t CPL_DLL CPLVirtualMemGetPageSize(CPLVirtualMem* ctxt);
  
  /** Return TRUE if this memory mapping can be accessed safely from concurrent
   *  threads.
   *
   * The situation that can cause problems is when several threads try to access
   * a page of the mapping that is not yet mapped.
   *
   * The return value of this function depends on whether bSingleThreadUsage has
   * been set of not in CPLVirtualMemNew() and/or the implementation.
   *
   * On Linux, this will always return TRUE if bSingleThreadUsage = FALSE.
   *
   * @param ctxt context returned by CPLVirtualMemNew().
   * @return TRUE if this memory mapping can be accessed safely from concurrent
   *         threads.
   *
   * @since GDAL 1.11
   */
  int CPL_DLL CPLVirtualMemIsAccessThreadSafe(CPLVirtualMem* ctxt);
  
  /** Declare that a thread will access a virtual memory mapping.
   *
   * This function must be called by a thread that wants to access the
   * content of a virtual memory mapping, except if the virtual memory mapping has
   * been created with bSingleThreadUsage = TRUE.
   *
   * This function must be paired with CPLVirtualMemUnDeclareThread().
   *
   * @param ctxt context returned by CPLVirtualMemNew().
   *
   * @since GDAL 1.11
   */
  void CPL_DLL CPLVirtualMemDeclareThread(CPLVirtualMem* ctxt);
  
  /** Declare that a thread will stop accessing a virtual memory mapping.
   *
   * This function must be called by a thread that will no longer access the
   * content of a virtual memory mapping, except if the virtual memory mapping has
   * been created with bSingleThreadUsage = TRUE.
   *
   * This function must be paired with CPLVirtualMemDeclareThread().
   *
   * @param ctxt context returned by CPLVirtualMemNew().
   *
   * @since GDAL 1.11
   */
  void CPL_DLL CPLVirtualMemUnDeclareThread(CPLVirtualMem* ctxt);
  
  /** Make sure that a region of virtual memory will be realized.
   *
   * Calling this function is not required, but might be useful when debugging
   * a process with tools like gdb or valgrind that do not naturally like
   * segmentation fault signals.
   *
   * It is also needed when wanting to provide part of virtual memory mapping
   * to a system call such as read() or write(). If read() or write() is called
   * on a memory region not yet realized, the call will fail with EFAULT.
   *
   * @param ctxt context returned by CPLVirtualMemNew().
   * @param pAddr the memory region to pin.
   * @param nSize the size of the memory region.
   * @param bWriteOp set to TRUE if the memory are will be accessed in write mode.
   *
   * @since GDAL 1.11
   */
  void CPL_DLL CPLVirtualMemPin(CPLVirtualMem* ctxt,
                                void* pAddr, size_t nSize, int bWriteOp);
  
  /** Cleanup any resource and handlers related to virtual memory.
   *
   * This function must be called after the last CPLVirtualMem object has
   * been freed.
   *
   * @since GDAL 2.0
   */
  void CPL_DLL CPLVirtualMemManagerTerminate(void);
  
  
  CPL_C_END
  
  #endif /* _CPL_VIRTUAL_MEM_INCLUDED */
  