/********************************************************************** * $Id: cpl_virtualmem.h 29330 2015-06-14 12:11:11Z rouault $ * * Name: cpl_virtualmem.h * Project: CPL - Common Portability Library * Purpose: Virtual memory * Author: Even Rouault, * ********************************************************************** * Copyright (c) 2014, Even Rouault * * 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 */