Updating XTBs based on .GRDs from branch master
[chromium-blink-merge.git] / chrome / app / image_pre_reader_win.h
blobe32e019049c802901464719d1c7e5fdc36226fb7
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.
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.
9 #ifndef CHROME_APP_IMAGE_PRE_READER_WIN_H_
10 #define CHROME_APP_IMAGE_PRE_READER_WIN_H_
12 #include "base/basictypes.h"
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.
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);
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.
35 // This function checks the Windows version to determine which pre-reading
36 // mechanism to use.
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.
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).
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);
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);
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
73 #endif // CHROME_APP_IMAGE_PRE_READER_WIN_H_