366 lines
14 KiB
C
366 lines
14 KiB
C
/**********************************************************************
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* $Id$
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*
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* Name: cpl_virtualmem.h
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* Project: CPL - Common Portability Library
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* Purpose: Virtual memory
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* Author: Even Rouault, <even dot rouault at spatialys.com>
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*
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**********************************************************************
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* Copyright (c) 2014, Even Rouault <even dot rouault at spatialys.com>
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*
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* SPDX-License-Identifier: MIT
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****************************************************************************/
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#ifndef CPL_VIRTUAL_MEM_INCLUDED
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#define CPL_VIRTUAL_MEM_INCLUDED
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#include <stddef.h>
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#include "cpl_port.h"
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#include "cpl_vsi.h"
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CPL_C_START
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/**
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* \file cpl_virtualmem.h
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*
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* Virtual memory management.
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*
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* This file provides mechanism to define virtual memory mappings, whose content
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* is allocated transparently and filled on-the-fly. Those virtual memory
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* mappings can be much larger than the available RAM, but only parts of the
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* virtual memory mapping, in the limit of the allowed the cache size, will
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* actually be physically allocated.
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*
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* This exploits low-level mechanisms of the operating system (virtual memory
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* allocation, page protection and handler of virtual memory exceptions).
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*
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* It is also possible to create a virtual memory mapping from a file or part
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* of a file.
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*
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* The current implementation is Linux only.
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*/
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/** Opaque type that represents a virtual memory mapping. */
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typedef struct CPLVirtualMem CPLVirtualMem;
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/** Callback triggered when a still unmapped page of virtual memory is accessed.
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* The callback has the responsibility of filling the page with relevant values
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*
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* @param ctxt virtual memory handle.
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* @param nOffset offset of the page in the memory mapping.
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* @param pPageToFill address of the page to fill. Note that the address might
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* be a temporary location, and not at CPLVirtualMemGetAddr()
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* + nOffset.
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* @param nToFill number of bytes of the page.
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* @param pUserData user data that was passed to CPLVirtualMemNew().
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*/
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typedef void (*CPLVirtualMemCachePageCbk)(CPLVirtualMem *ctxt, size_t nOffset,
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void *pPageToFill, size_t nToFill,
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void *pUserData);
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/** Callback triggered when a dirty mapped page is going to be freed.
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* (saturation of cache, or termination of the virtual memory mapping).
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*
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* @param ctxt virtual memory handle.
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* @param nOffset offset of the page in the memory mapping.
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* @param pPageToBeEvicted address of the page that will be flushed. Note that
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* the address might be a temporary location, and not at CPLVirtualMemGetAddr()
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* + nOffset.
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* @param nToBeEvicted number of bytes of the page.
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* @param pUserData user data that was passed to CPLVirtualMemNew().
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*/
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typedef void (*CPLVirtualMemUnCachePageCbk)(CPLVirtualMem *ctxt, size_t nOffset,
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const void *pPageToBeEvicted,
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size_t nToBeEvicted,
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void *pUserData);
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/** Callback triggered when a virtual memory mapping is destroyed.
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* @param pUserData user data that was passed to CPLVirtualMemNew().
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*/
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typedef void (*CPLVirtualMemFreeUserData)(void *pUserData);
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/** Access mode of a virtual memory mapping. */
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typedef enum
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{
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/*! The mapping is meant at being read-only, but writes will not be
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prevented. Note that any content written will be lost. */
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VIRTUALMEM_READONLY,
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/*! The mapping is meant at being read-only, and this will be enforced
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through the operating system page protection mechanism. */
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VIRTUALMEM_READONLY_ENFORCED,
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/*! The mapping is meant at being read-write, and modified pages can be
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saved thanks to the pfnUnCachePage callback */
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VIRTUALMEM_READWRITE
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} CPLVirtualMemAccessMode;
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/** Return the size of a page of virtual memory.
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*
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* @return the page size.
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*
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* @since GDAL 1.11
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*/
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size_t CPL_DLL CPLGetPageSize(void);
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/** Create a new virtual memory mapping.
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*
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* This will reserve an area of virtual memory of size nSize, whose size
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* might be potentially much larger than the physical memory available.
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* Initially, no physical memory will be allocated. As soon as memory pages will
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* be accessed, they will be allocated transparently and filled with the
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* pfnCachePage callback. When the allowed cache size is reached, the least
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* recently used pages will be unallocated.
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*
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* On Linux AMD64 platforms, the maximum value for nSize is 128 TB.
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* On Linux x86 platforms, the maximum value for nSize is 2 GB.
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*
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* Only supported on Linux for now.
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*
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* Note that on Linux, this function will install a SIGSEGV handler. The
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* original handler will be restored by CPLVirtualMemManagerTerminate().
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*
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* @param nSize size in bytes of the virtual memory mapping.
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* @param nCacheSize size in bytes of the maximum memory that will be really
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* allocated (must ideally fit into RAM).
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* @param nPageSizeHint hint for the page size. Must be a multiple of the
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* system page size, returned by CPLGetPageSize().
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* Minimum value is generally 4096. Might be set to 0 to
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* let the function determine a default page size.
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* @param bSingleThreadUsage set to TRUE if there will be no concurrent threads
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* that will access the virtual memory mapping. This
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* can optimize performance a bit.
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* @param eAccessMode permission to use for the virtual memory mapping.
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* @param pfnCachePage callback triggered when a still unmapped page of virtual
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* memory is accessed. The callback has the responsibility
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* of filling the page with relevant values.
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* @param pfnUnCachePage callback triggered when a dirty mapped page is going to
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* be freed (saturation of cache, or termination of the
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* virtual memory mapping). Might be NULL.
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* @param pfnFreeUserData callback that can be used to free pCbkUserData. Might
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* be NULL
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* @param pCbkUserData user data passed to pfnCachePage and pfnUnCachePage.
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*
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* @return a virtual memory object that must be freed by CPLVirtualMemFree(),
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* or NULL in case of failure.
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*
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* @since GDAL 1.11
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*/
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CPLVirtualMem CPL_DLL *
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CPLVirtualMemNew(size_t nSize, size_t nCacheSize, size_t nPageSizeHint,
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int bSingleThreadUsage, CPLVirtualMemAccessMode eAccessMode,
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CPLVirtualMemCachePageCbk pfnCachePage,
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CPLVirtualMemUnCachePageCbk pfnUnCachePage,
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CPLVirtualMemFreeUserData pfnFreeUserData, void *pCbkUserData);
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/** Return if virtual memory mapping of a file is available.
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*
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* @return TRUE if virtual memory mapping of a file is available.
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* @since GDAL 1.11
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*/
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int CPL_DLL CPLIsVirtualMemFileMapAvailable(void);
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/** Create a new virtual memory mapping from a file.
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*
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* The file must be a "real" file recognized by the operating system, and not
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* a VSI extended virtual file.
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*
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* In VIRTUALMEM_READWRITE mode, updates to the memory mapping will be written
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* in the file.
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*
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* On Linux AMD64 platforms, the maximum value for nLength is 128 TB.
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* On Linux x86 platforms, the maximum value for nLength is 2 GB.
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*
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* Supported on Linux only in GDAL <= 2.0, and all POSIX systems supporting
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* mmap() in GDAL >= 2.1
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*
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* @param fp Virtual file handle.
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* @param nOffset Offset in the file to start the mapping from.
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* @param nLength Length of the portion of the file to map into memory.
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* @param eAccessMode Permission to use for the virtual memory mapping. This
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* must be consistent with how the file has been opened.
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* @param pfnFreeUserData callback that is called when the object is destroyed.
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* @param pCbkUserData user data passed to pfnFreeUserData.
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* @return a virtual memory object that must be freed by CPLVirtualMemFree(),
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* or NULL in case of failure.
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*
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* @since GDAL 1.11
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*/
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CPLVirtualMem CPL_DLL *CPLVirtualMemFileMapNew(
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VSILFILE *fp, vsi_l_offset nOffset, vsi_l_offset nLength,
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CPLVirtualMemAccessMode eAccessMode,
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CPLVirtualMemFreeUserData pfnFreeUserData, void *pCbkUserData);
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/** Create a new virtual memory mapping derived from an other virtual memory
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* mapping.
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*
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* This may be useful in case of creating mapping for pixel interleaved data.
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*
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* The new mapping takes a reference on the base mapping.
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*
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* @param pVMemBase Base virtual memory mapping
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* @param nOffset Offset in the base virtual memory mapping from which to
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* start the new mapping.
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* @param nSize Size of the base virtual memory mapping to expose in the
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* the new mapping.
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* @param pfnFreeUserData callback that is called when the object is destroyed.
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* @param pCbkUserData user data passed to pfnFreeUserData.
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* @return a virtual memory object that must be freed by CPLVirtualMemFree(),
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* or NULL in case of failure.
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*
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* @since GDAL 1.11
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*/
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CPLVirtualMem CPL_DLL *CPLVirtualMemDerivedNew(
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CPLVirtualMem *pVMemBase, vsi_l_offset nOffset, vsi_l_offset nSize,
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CPLVirtualMemFreeUserData pfnFreeUserData, void *pCbkUserData);
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/** Free a virtual memory mapping.
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*
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* The pointer returned by CPLVirtualMemGetAddr() will no longer be valid.
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* If the virtual memory mapping was created with read/write permissions and
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* that they are dirty (i.e. modified) pages, they will be flushed through the
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* pfnUnCachePage callback before being freed.
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*
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* @param ctxt context returned by CPLVirtualMemNew().
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*
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* @since GDAL 1.11
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*/
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void CPL_DLL CPLVirtualMemFree(CPLVirtualMem *ctxt);
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/** Return the pointer to the start of a virtual memory mapping.
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*
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* The bytes in the range [p:p+CPLVirtualMemGetSize()-1] where p is the pointer
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* returned by this function will be valid, until CPLVirtualMemFree() is called.
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*
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* Note that if a range of bytes used as an argument of a system call
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* (such as read() or write()) contains pages that have not been "realized", the
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* system call will fail with EFAULT. CPLVirtualMemPin() can be used to work
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* around this issue.
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*
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* @param ctxt context returned by CPLVirtualMemNew().
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* @return the pointer to the start of a virtual memory mapping.
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*
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* @since GDAL 1.11
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*/
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void CPL_DLL *CPLVirtualMemGetAddr(CPLVirtualMem *ctxt);
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/** Return the size of the virtual memory mapping.
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*
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* @param ctxt context returned by CPLVirtualMemNew().
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* @return the size of the virtual memory mapping.
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*
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* @since GDAL 1.11
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*/
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size_t CPL_DLL CPLVirtualMemGetSize(CPLVirtualMem *ctxt);
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/** Return if the virtual memory mapping is a direct file mapping.
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*
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* @param ctxt context returned by CPLVirtualMemNew().
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* @return TRUE if the virtual memory mapping is a direct file mapping.
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*
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* @since GDAL 1.11
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*/
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int CPL_DLL CPLVirtualMemIsFileMapping(CPLVirtualMem *ctxt);
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/** Return the access mode of the virtual memory mapping.
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*
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* @param ctxt context returned by CPLVirtualMemNew().
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* @return the access mode of the virtual memory mapping.
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*
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* @since GDAL 1.11
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*/
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CPLVirtualMemAccessMode CPL_DLL CPLVirtualMemGetAccessMode(CPLVirtualMem *ctxt);
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/** Return the page size associated to a virtual memory mapping.
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*
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* The value returned will be at least CPLGetPageSize(), but potentially
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* larger.
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*
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* @param ctxt context returned by CPLVirtualMemNew().
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* @return the page size
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*
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* @since GDAL 1.11
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*/
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size_t CPL_DLL CPLVirtualMemGetPageSize(CPLVirtualMem *ctxt);
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/** Return TRUE if this memory mapping can be accessed safely from concurrent
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* threads.
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*
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* The situation that can cause problems is when several threads try to access
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* a page of the mapping that is not yet mapped.
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*
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* The return value of this function depends on whether bSingleThreadUsage has
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* been set of not in CPLVirtualMemNew() and/or the implementation.
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*
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* On Linux, this will always return TRUE if bSingleThreadUsage = FALSE.
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*
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* @param ctxt context returned by CPLVirtualMemNew().
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* @return TRUE if this memory mapping can be accessed safely from concurrent
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* threads.
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*
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* @since GDAL 1.11
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*/
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int CPL_DLL CPLVirtualMemIsAccessThreadSafe(CPLVirtualMem *ctxt);
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/** Declare that a thread will access a virtual memory mapping.
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*
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* This function must be called by a thread that wants to access the
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* content of a virtual memory mapping, except if the virtual memory mapping has
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* been created with bSingleThreadUsage = TRUE.
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*
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* This function must be paired with CPLVirtualMemUnDeclareThread().
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*
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* @param ctxt context returned by CPLVirtualMemNew().
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*
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* @since GDAL 1.11
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*/
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void CPL_DLL CPLVirtualMemDeclareThread(CPLVirtualMem *ctxt);
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/** Declare that a thread will stop accessing a virtual memory mapping.
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*
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* This function must be called by a thread that will no longer access the
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* content of a virtual memory mapping, except if the virtual memory mapping has
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* been created with bSingleThreadUsage = TRUE.
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*
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* This function must be paired with CPLVirtualMemDeclareThread().
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*
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* @param ctxt context returned by CPLVirtualMemNew().
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*
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* @since GDAL 1.11
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*/
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void CPL_DLL CPLVirtualMemUnDeclareThread(CPLVirtualMem *ctxt);
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/** Make sure that a region of virtual memory will be realized.
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*
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* Calling this function is not required, but might be useful when debugging
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* a process with tools like gdb or valgrind that do not naturally like
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* segmentation fault signals.
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*
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* It is also needed when wanting to provide part of virtual memory mapping
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* to a system call such as read() or write(). If read() or write() is called
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* on a memory region not yet realized, the call will fail with EFAULT.
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*
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* @param ctxt context returned by CPLVirtualMemNew().
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* @param pAddr the memory region to pin.
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* @param nSize the size of the memory region.
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* @param bWriteOp set to TRUE if the memory are will be accessed in write mode.
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*
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* @since GDAL 1.11
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*/
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void CPL_DLL CPLVirtualMemPin(CPLVirtualMem *ctxt, void *pAddr, size_t nSize,
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int bWriteOp);
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/** Cleanup any resource and handlers related to virtual memory.
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*
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* This function must be called after the last CPLVirtualMem object has
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* been freed.
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*
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* @since GDAL 2.0
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*/
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void CPL_DLL CPLVirtualMemManagerTerminate(void);
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CPL_C_END
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#endif /* CPL_VIRTUAL_MEM_INCLUDED */
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