blob: b34530097e565ca4da556baa4a72a28200393c9d [file] [log] [blame]
// 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.
#include "chrome/app/file_pre_reader_win.h"
#include <windows.h>
#include <memoryapi.h> // NOLINT(build/include_order)
#include "base/files/file.h"
#include "base/files/memory_mapped_file.h"
void PreReadFile(const base::FilePath& file_path) {
// On Win8 and higher use ::PrefetchVirtualMemory(). This is better than
// a simple data file read, more from a RAM perspective than CPU. This is
// because reading the file as data results in double mapping to
// Image/executable pages for all pages of code executed. On Win7 just do a
// simple file read as data.
// ::PrefetchVirtualMemory() isn't available on Win7.
HMODULE kernel32_library = GetModuleHandleA("kernel32.dll");
auto prefetch_virtual_memory =
GetProcAddress(kernel32_library, "PrefetchVirtualMemory"));
if (!prefetch_virtual_memory) {
// On Win7 read in the file as data since the OS doesn't have
// the support for better options.
constexpr DWORD kStepSize = 1024 * 1024;
base::File file(file_path, base::File::FLAG_OPEN | base::File::FLAG_READ |
if (!file.IsValid())
char* buffer = reinterpret_cast<char*>(
::VirtualAlloc(nullptr, kStepSize, MEM_COMMIT, PAGE_READWRITE));
if (!buffer)
while (file.ReadAtCurrentPos(buffer, kStepSize) > 0) {
::VirtualFree(buffer, 0, MEM_RELEASE);
} else {
// NB: Creating the file mapping before the ::LoadLibrary() of the file is
// more efficient memory wise, but we must be sure no other threads try to
// loadlibrary the file while we are doing the mapping and prefetching or
// the process will get a private copy of the DLL via COW.
base::MemoryMappedFile mapped_file;
if (mapped_file.Initialize(file_path,
base::MemoryMappedFile::READ_CODE_IMAGE)) {
_WIN32_MEMORY_RANGE_ENTRY address_range = {,
// NB: PrefetchVirtualMemory requires the file to be opened with
// only read access or it will fail.
(*prefetch_virtual_memory)(GetCurrentProcess(), 1, &address_range, 0);