/**********************************************************************
* $Id: cpl_virtualmem.h 33666 2016-03-07 05:21:07Z goatbar $
*
* 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.
*
* Supported on Linux only in GDAL <= 2.0, and all POSIX systems supporting
* mmap() in GDAL >= 2.1
*
* @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 virtual memory mapping is a direct file mapping.
*
* @param ctxt context returned by CPLVirtualMemNew().
* @return TRUE if the virtual 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 */