chrome/app/image_pre_reader_win.h

   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 // This file defines utility functions to pre-read a PE Image in order to
   6 // avoid hard page faults when the image is subsequently loaded into memory
   7 // for execution.
   8
   9 #ifndef CHROME_APP_IMAGE_PRE_READER_WIN_H_
  10 #define CHROME_APP_IMAGE_PRE_READER_WIN_H_
  11
  12 #include "base/basictypes.h"
  13
  14 // This class defines static helper functions to pre-read a PE Image in order
  15 // to avoid hard page faults when the image is subsequently loaded into memory
  16 // for execution.
  17 class ImagePreReader {
  18  public:
  19   // Reads the file passed in as a PE Image and touches pages to avoid
  20   // subsequent hard page faults during LoadLibrary. The size to be pre-read
  21   // is passed in. If it is 0 then the whole file is paged in. The step size
  22   // which indicates the number of bytes to skip after every page touched is
  23   // also passed in.
  24   //
  25   // This function checks the Windows version to determine which pre-reading
  26   // mechanism to use.
  27   static bool PreReadImage(const wchar_t* file_path,
  28                            size_t size_to_read,
  29                            size_t step_size);
  30
  31   // Loads the file passed in as PE Image and touches a percentage of the
  32   // pages in each of the image's sections to avoid subsequent hard page
  33   // faults during LoadLibrary.
  34   //
  35   // This function checks the Windows version to determine which pre-reading
  36   // mechanism to use.
  37   //
  38   // The percentage of the file to be read is an integral value between 0 and
  39   // 100, inclusive. If it is 0 then this is a NOP, if it is 100 (or greater)
  40   // then the whole file is paged in sequentially via PreReadImage. Otherwise,
  41   // for each section, in order, the given percentage of the blocks in that
  42   // section are paged in, starting at the beginning of each section. For
  43   // example: if percentage is 30 and there is a .text section and a .data
  44   // section, then the first 30% of .text will be paged and the first 30% of
  45   // .data will be paged in.
  46   //
  47   // The max_chunk_size indicates the number of bytes to read off the disk in
  48   // each step (for Vista and greater, where this is the way the pages are
  49   // warmed).
  50   //
  51   // This function is intended to be used in the context of a PE image with
  52   // an optimized layout, such that the blocks in each section are arranged
  53   // with the data and code most needed for startup moved to the front.
  54   // See also: http://code.google.com/p/chromium/issues/detail?id=98508
  55   static bool PartialPreReadImage(const wchar_t* file_path,
  56                                   size_t percentage,
  57                                   size_t max_chunk_size);
  58
  59   // Helper function used by PartialPreReadImage on Windows versions (Vista+)
  60   // where reading through the file on disk serves to warm up the page cache.
  61   // Exported for unit-testing purposes.
  62   static bool PartialPreReadImageOnDisk(const wchar_t* file_path,
  63                                         size_t percentage,
  64                                         size_t max_chunk_size);
  65
  66   // Helper function used by PartialPreReadImage on Windows versions (XP) where
  67   // cheaply loading the image then stepping through its address space serves
  68   // to warm up the page cache. Exported for unit-testing purposes.
  69   static bool PartialPreReadImageInMemory(const wchar_t* file_path,
  70                                           size_t percentage);
  71 };  // namespace internal
  72
  73 #endif  // CHROME_APP_IMAGE_PRE_READER_WIN_H_