Transform ImagePreReader into PreReadFile.

chrome/app/file_pre_reader_win.cc

Index: chrome/app/file_pre_reader_win.cc
diff --git a/chrome/app/file_pre_reader_win.cc b/chrome/app/file_pre_reader_win.cc
new file mode 100644
index 0000000000000000000000000000000000000000..43edde879c3bdd67a0651fb620af8e3e1016f219
--- /dev/null
+++ b/chrome/app/file_pre_reader_win.cc
@@ -0,0 +1,83 @@
+// 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 "base/files/file.h"
+#include "base/files/memory_mapped_file.h"
+#include "base/logging.h"
+#include "base/threading/thread_restrictions.h"
+#include "base/win/windows_version.h"
+
+namespace {
+
+// A helper function to touch all pages in the range
+// [base_addr, base_addr + length).
+void TouchPagesInRange(const void* base_addr, size_t length) {
+  DCHECK(base_addr != NULL);

[grt (UTC plus 2), 2015/11/03 04:02:15]

DCHECK(base_addr);

[fdoray, 2015/11/03 21:23:39]

Done.

+  DCHECK(length > 0);

[grt (UTC plus 2), 2015/11/03 04:02:15]

DCHECK_GT

[fdoray, 2015/11/03 21:23:39]

Done.

+
+  // Get the system info so we know the page size. Also, make sure we use a
+  // non-zero value for the page size; GetSystemInfo() is hookable/patchable,
+  // and you never know what shenanigans someone could get up to.
+  SYSTEM_INFO system_info = {};
+  ::GetSystemInfo(&system_info);
+  if (system_info.dwPageSize == 0)
+    system_info.dwPageSize = 4096;
+
+  // We don't want to read outside the byte range (which could trigger an
+  // access violation), so let's figure out the exact locations of the first
+  // and final bytes we want to read.
+  volatile uint8_t const* touch_ptr =
+      reinterpret_cast<uint8_t const*>(base_addr);
+  volatile uint8_t const* final_touch_ptr = touch_ptr + length - 1;
+
+  // Read the memory in the range [touch_ptr, final_touch_ptr] with a stride
+  // of the system page size, to ensure that it's been paged in.
+  uint8_t dummy;
+  while (touch_ptr < final_touch_ptr) {

[grt (UTC plus 2), 2015/11/03 04:02:15]

  for (; touch_ptr < final_touch_ptr; touch_ptr += system_info.dwPageSize)
    dummy = *touch_ptr;

[fdoray, 2015/11/03 21:23:39]

Done.

+    dummy = *touch_ptr;
+    touch_ptr += system_info.dwPageSize;
+  }
+  dummy = *final_touch_ptr;
+}
+
+}  // namespace
+
+bool PreReadFile(const base::FilePath& file_path, int step_size) {
+  DCHECK(step_size > 0);

[grt (UTC plus 2), 2015/11/03 04:02:14]

DCHECK_GT

[fdoray, 2015/11/03 21:23:39]

Done.

+  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.
+    base::File file(file_path, base::File::FLAG_OPEN | base::File::FLAG_READ |
+                                   base::File::FLAG_SEQUENTIAL_SCAN);
+    if (!file.IsValid())
+      return false;
+
+    LPVOID buffer = ::VirtualAlloc(NULL, static_cast<DWORD>(step_size),

[grt (UTC plus 2), 2015/11/03 04:02:15]

nullptr

[fdoray, 2015/11/03 21:23:39]

Done.

+                                   MEM_COMMIT, PAGE_READWRITE);
+    if (buffer == NULL)

[grt (UTC plus 2), 2015/11/03 04:02:15]

nullptr or "if (!buffer)"

[fdoray, 2015/11/03 21:23:39]

Done.

+      return false;
+
+    while (file.ReadAtCurrentPos(buffer, step_size) > 0) {

[grt (UTC plus 2), 2015/11/03 04:02:15]

nit: while(...);

[fdoray, 2015/11/03 21:23:39]

while(); generates a pre-submit warning.

"Empty loop bodies should use {} or continue, but not a single semicolon."
https://google.github.io/styleguide/cppguide.html#Loops_and_Switch_Statements

[grt (UTC plus 2), 2015/11/03 21:32:50]

ah, i didn't know that. thanks.

+    }
+
+    ::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 and touch pages at a stride. We use
+    // the system's page size as the stride, ignoring the passed in step_size,
+    // to make sure each page in the range is touched.
+    base::MemoryMappedFile file_memory_map;
+    if (!file_memory_map.Initialize(base::FilePath(file_path)))

[grt (UTC plus 2), 2015/11/03 04:02:15]

omit base::FilePath

[fdoray, 2015/11/03 21:23:39]

Done.

+      return false;
+    TouchPagesInRange(file_memory_map.data(), file_memory_map.length());
+  }
+
+  return true;
+}