net/disk_cache/mapped_file_avoid_mmap_posix.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "net/disk_cache/mapped_file.h"
   6
   7 #include <stdlib.h>
   8
   9 #include "base/files/file_path.h"
  10 #include "base/logging.h"
  11
  12 namespace disk_cache {
  13
  14 void* MappedFile::Init(const base::FilePath& name, size_t size) {
  15   DCHECK(!init_);
  16   if (init_ || !File::Init(name))
  17     return NULL;
  18
  19   if (!size)
  20     size = GetLength();
  21
  22   buffer_ = malloc(size);
  23   snapshot_ = malloc(size);
  24   if (buffer_ && snapshot_ && Read(buffer_, size, 0)) {
  25     memcpy(snapshot_, buffer_, size);
  26   } else {
  27     free(buffer_);
  28     free(snapshot_);
  29     buffer_ = snapshot_ = 0;
  30   }
  31
  32   init_ = true;
  33   view_size_ = size;
  34   return buffer_;
  35 }
  36
  37 bool MappedFile::Load(const FileBlock* block) {
  38   size_t offset = block->offset() + view_size_;
  39   return Read(block->buffer(), block->size(), offset);
  40 }
  41
  42 bool MappedFile::Store(const FileBlock* block) {
  43   size_t offset = block->offset() + view_size_;
  44   return Write(block->buffer(), block->size(), offset);
  45 }
  46
  47 void MappedFile::Flush() {
  48   DCHECK(buffer_);
  49   DCHECK(snapshot_);
  50   if (0 == memcmp(buffer_, snapshot_, view_size_)) {
  51     // Nothing changed, no need to flush.
  52     return;
  53   }
  54
  55   const char* buffer_ptr = static_cast<const char*>(buffer_);
  56   char* snapshot_ptr = static_cast<char*>(snapshot_);
  57   size_t i = 0;
  58   while (i < view_size_) {
  59     size_t run_start = i;
  60     // Look for a run of changed bytes (possibly zero-sized). Write them out.
  61     while(i < view_size_ && snapshot_ptr[i] != buffer_ptr[i]) {
  62       snapshot_ptr[i] = buffer_ptr[i];
  63       i++;
  64     }
  65     if (i > run_start) {
  66       Write(snapshot_ptr + run_start, i - run_start, run_start);
  67     }
  68     // Look for a run of unchanged bytes (possibly zero-sized). Skip them.
  69     while (i < view_size_ && snapshot_ptr[i] == buffer_ptr[i]) {
  70       i++;
  71     }
  72   }
  73   DCHECK(0 == memcmp(buffer_, snapshot_, view_size_));
  74 }
  75
  76 MappedFile::~MappedFile() {
  77   if (!init_)
  78     return;
  79
  80   if (buffer_ && snapshot_) {
  81     Flush();
  82   }
  83   free(buffer_);
  84   free(snapshot_);
  85 }
  86
  87 }  // namespace disk_cache