Add a PartialPreReadImage function to file_util (on Windows).

base/file_util_win.cc

 // 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 "base/file_util.h"
 
 #include <windows.h>
 #include <propvarutil.h>
 #include <psapi.h>
 #include <shellapi.h>
@@ skipping 1087 matching lines @@
   bool success = false;
   HANDLE cp = GetCurrentProcess();
   if (::GetMappedFileNameW(cp, file_view, mapped_file_path, kMaxPathLength)) {
     *nt_path = FilePath(mapped_file_path);
     success = true;
   }
   ::UnmapViewOfFile(file_view);
   return success;
 }
 
-bool PreReadImage(const wchar_t* file_path, size_t size_to_read,
-                  size_t step_size) {
-  base::ThreadRestrictions::AssertIOAllowed();
-  if (base::win::GetVersion() > base::win::VERSION_XP) {
-    // Vista+ branch. On these OSes, the forced reads through the DLL actually
-    // slows warm starts. The solution is to sequentially read file contents
-    // with an optional cap on total amount to read.
-    base::win::ScopedHandle file(
-        CreateFile(file_path,
-                   GENERIC_READ,
-                   FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
-                   NULL,
-                   OPEN_EXISTING,
-                   FILE_FLAG_SEQUENTIAL_SCAN,
-                   NULL));
-
-    if (!file.IsValid())
-      return false;
-
-    // Default to 1MB sequential reads.
-    const DWORD actual_step_size = std::max(static_cast<DWORD>(step_size),
-                                            static_cast<DWORD>(1024*1024));
-    LPVOID buffer = ::VirtualAlloc(NULL,
-                                   actual_step_size,
-                                   MEM_COMMIT,
-                                   PAGE_READWRITE);
-
-    if (buffer == NULL)
-      return false;
-
-    DWORD len;
-    size_t total_read = 0;
-    while (::ReadFile(file, buffer, actual_step_size, &len, NULL) &&
-           len > 0 &&
-           (size_to_read ? total_read < size_to_read : true)) {
-      total_read += static_cast<size_t>(len);
-    }
-    ::VirtualFree(buffer, 0, MEM_RELEASE);
-  } else {
-    // WinXP branch. Here, reading the DLL from disk doesn't do
-    // what we want so instead we pull the pages into memory by loading
-    // the DLL and touching pages at a stride.
-    HMODULE dll_module = ::LoadLibraryExW(
-        file_path,
-        NULL,
-        LOAD_WITH_ALTERED_SEARCH_PATH | DONT_RESOLVE_DLL_REFERENCES);
-
-    if (!dll_module)
-      return false;
-
-    base::win::PEImage pe_image(dll_module);
-    PIMAGE_NT_HEADERS nt_headers = pe_image.GetNTHeaders();
-    size_t actual_size_to_read = size_to_read ? size_to_read :
-                                 nt_headers->OptionalHeader.SizeOfImage;
-    volatile uint8* touch = reinterpret_cast<uint8*>(dll_module);
-    size_t offset = 0;
-    while (offset < actual_size_to_read) {
-      uint8 unused = *(touch + offset);
-      offset += step_size;
-    }
-    FreeLibrary(dll_module);
-  }
-
-  return true;
-}
-
 }  // namespace file_util