// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// This file defines utility functions to pre-read a PE Image in order to
// avoid hard page faults when the image is subsequently loaded into memory
// for execution.
#ifndef CHROME_APP_IMAGE_PRE_READER_WIN_H_
#define CHROME_APP_IMAGE_PRE_READER_WIN_H_
#include "base/basictypes.h"
// This class defines static helper functions to pre-read a PE Image in order
// to avoid hard page faults when the image is subsequently loaded into memory
// for execution.
class ImagePreReader {
public:
// Reads the file passed in as a PE Image and touches pages to avoid
// subsequent hard page faults during LoadLibrary. The size to be pre-read
// is passed in. If it is 0 then the whole file is paged in. The step size
// which indicates the number of bytes to skip after every page touched is
// also passed in.
//
// This function checks the Windows version to determine which pre-reading
// mechanism to use.
static bool PreReadImage(const wchar_t* file_path,
size_t size_to_read,
size_t step_size);
// Loads the file passed in as PE Image and touches a percentage of the
// pages in each of the image's sections to avoid subsequent hard page
// faults during LoadLibrary.
//
// This function checks the Windows version to determine which pre-reading
// mechanism to use.
//
// The percentage of the file to be read is an integral value between 0 and
// 100, inclusive. If it is 0 then this is a NOP, if it is 100 (or greater)
// then the whole file is paged in sequentially via PreReadImage. Otherwise,
// for each section, in order, the given percentage of the blocks in that
// section are paged in, starting at the beginning of each section. For
// example: if percentage is 30 and there is a .text section and a .data
// section, then the first 30% of .text will be paged and the first 30% of
// .data will be paged in.
//
// The max_chunk_size indicates the number of bytes to read off the disk in
// each step (for Vista and greater, where this is the way the pages are
// warmed).
//
// This function is intended to be used in the context of a PE image with
// an optimized layout, such that the blocks in each section are arranged
// with the data and code most needed for startup moved to the front.
// See also: http://code.google.com/p/chromium/issues/detail?id=98508
static bool PartialPreReadImage(const wchar_t* file_path,
size_t percentage,
size_t max_chunk_size);
// Helper function used by PartialPreReadImage on Windows versions (Vista+)
// where reading through the file on disk serves to warm up the page cache.
// Exported for unit-testing purposes.
static bool PartialPreReadImageOnDisk(const wchar_t* file_path,
size_t percentage,
size_t max_chunk_size);
// Helper function used by PartialPreReadImage on Windows versions (XP) where
// cheaply loading the image then stepping through its address space serves
// to warm up the page cache. Exported for unit-testing purposes.
static bool PartialPreReadImageInMemory(const wchar_t* file_path,
size_t percentage);
}; // namespace internal
#endif // CHROME_APP_IMAGE_PRE_READER_WIN_H_