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137 lines
4.9 KiB
137 lines
4.9 KiB
// Copyright 2013 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_FILES_MEMORY_MAPPED_FILE_H_
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#define BASE_FILES_MEMORY_MAPPED_FILE_H_
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#include <stddef.h>
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#include <stdint.h>
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#include "base/base_export.h"
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#include "base/files/file.h"
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#include "base/macros.h"
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#include "build/build_config.h"
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#if defined(OS_WIN)
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#include <windows.h>
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#endif
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namespace base {
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class FilePath;
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class BASE_EXPORT MemoryMappedFile {
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public:
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enum Access {
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// Mapping a file into memory effectively allows for file I/O on any thread.
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// The accessing thread could be paused while data from the file is paged
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// into memory. Worse, a corrupted filesystem could cause a SEGV within the
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// program instead of just an I/O error.
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READ_ONLY,
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// This provides read/write access to a file and must be used with care of
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// the additional subtleties involved in doing so. Though the OS will do
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// the writing of data on its own time, too many dirty pages can cause
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// the OS to pause the thread while it writes them out. The pause can
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// be as much as 1s on some systems.
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READ_WRITE,
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// This provides read/write access but with the ability to write beyond
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// the end of the existing file up to a maximum size specified as the
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// "region". Depending on the OS, the file may or may not be immediately
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// extended to the maximum size though it won't be loaded in RAM until
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// needed. Note, however, that the maximum size will still be reserved
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// in the process address space.
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READ_WRITE_EXTEND,
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};
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// The default constructor sets all members to invalid/null values.
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MemoryMappedFile();
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~MemoryMappedFile();
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// Used to hold information about a region [offset + size] of a file.
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struct BASE_EXPORT Region {
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static const Region kWholeFile;
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bool operator==(const Region& other) const;
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bool operator!=(const Region& other) const;
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// Start of the region (measured in bytes from the beginning of the file).
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int64_t offset;
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// Length of the region in bytes.
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size_t size;
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};
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// Opens an existing file and maps it into memory. |access| can be read-only
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// or read/write but not read/write+extend. If this object already points
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// to a valid memory mapped file then this method will fail and return
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// false. If it cannot open the file, the file does not exist, or the
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// memory mapping fails, it will return false.
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bool Initialize(const FilePath& file_name, Access access);
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bool Initialize(const FilePath& file_name) {
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return Initialize(file_name, READ_ONLY);
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}
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// As above, but works with an already-opened file. |access| can be read-only
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// or read/write but not read/write+extend. MemoryMappedFile takes ownership
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// of |file| and closes it when done. |file| must have been opened with
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// permissions suitable for |access|. If the memory mapping fails, it will
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// return false.
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bool Initialize(File file, Access access);
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bool Initialize(File file) {
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return Initialize(std::move(file), READ_ONLY);
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}
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// As above, but works with a region of an already-opened file. All forms of
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// |access| are allowed. If READ_WRITE_EXTEND is specified then |region|
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// provides the maximum size of the file. If the memory mapping fails, it
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// return false.
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bool Initialize(File file, const Region& region, Access access);
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bool Initialize(File file, const Region& region) {
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return Initialize(std::move(file), region, READ_ONLY);
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}
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const uint8_t* data() const { return data_; }
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uint8_t* data() { return data_; }
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size_t length() const { return length_; }
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// Is file_ a valid file handle that points to an open, memory mapped file?
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bool IsValid() const;
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private:
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// Given the arbitrarily aligned memory region [start, size], returns the
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// boundaries of the region aligned to the granularity specified by the OS,
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// (a page on Linux, ~32k on Windows) as follows:
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// - |aligned_start| is page aligned and <= |start|.
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// - |aligned_size| is a multiple of the VM granularity and >= |size|.
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// - |offset| is the displacement of |start| w.r.t |aligned_start|.
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static void CalculateVMAlignedBoundaries(int64_t start,
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size_t size,
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int64_t* aligned_start,
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size_t* aligned_size,
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int32_t* offset);
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// Map the file to memory, set data_ to that memory address. Return true on
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// success, false on any kind of failure. This is a helper for Initialize().
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bool MapFileRegionToMemory(const Region& region, Access access);
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// Closes all open handles.
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void CloseHandles();
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File file_;
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uint8_t* data_;
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size_t length_;
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#if defined(OS_WIN)
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win::ScopedHandle file_mapping_;
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#endif
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DISALLOW_COPY_AND_ASSIGN(MemoryMappedFile);
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};
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} // namespace base
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#endif // BASE_FILES_MEMORY_MAPPED_FILE_H_
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