Greatly reduce the race window in ProcessSingleton...

chrome/browser/process_singleton_win.cc

 // Copyright (c) 2009 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/browser/process_singleton.h"
 
 #include "base/base_paths.h"
 #include "base/command_line.h"
 #include "base/process_util.h"
 #include "base/win_util.h"
 #include "chrome/browser/browser_init.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/profile.h"
 #include "chrome/browser/profile_manager.h"
 #include "chrome/common/chrome_constants.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/l10n_util.h"
 #include "chrome/common/result_codes.h"
 #include "chrome/common/win_util.h"
 #include "grit/chromium_strings.h"
 #include "grit/generated_resources.h"
 
 namespace {
 
-// Checks the visiblilty of the enumerated window and signals once a visible
+// Checks the visibility of the enumerated window and signals once a visible
 // window has been found.
 BOOL CALLBACK BrowserWindowEnumeration(HWND window, LPARAM param) {
   bool* result = reinterpret_cast<bool*>(param);
   *result = IsWindowVisible(window) != 0;
   // Stops enumeration if a visible window has been found.
   return !*result;
 }
 
 }  // namespace
 
+// Look for a Chrome instance that uses the same profile directory.
 ProcessSingleton::ProcessSingleton(const FilePath& user_data_dir)
-    : window_(NULL),
-      locked_(false) {
-  // Look for a Chrome instance that uses the same profile directory:
-  remote_window_ = FindWindowEx(HWND_MESSAGE,
-                                NULL,
-                                chrome::kMessageWindowClass,
+    : window_(NULL), locked_(false) {
+  // FindWindoEx and Create() should be one atomic operation in order to not
+  // have a race condition.
+  remote_window_ = FindWindowEx(HWND_MESSAGE, NULL, chrome::kMessageWindowClass,
                                 user_data_dir.ToWStringHack().c_str());
+  if (!remote_window_)
+    Create();
 }
 
 ProcessSingleton::~ProcessSingleton() {
   if (window_)
     DestroyWindow(window_);
 }
 
 bool ProcessSingleton::NotifyOtherProcess() {
   if (!remote_window_)
     return false;
@@ skipping 65 matching lines @@
       return true;
     }
   }
 
   // Time to take action. Kill the browser process.
   base::KillProcessById(process_id, ResultCodes::HUNG, true);
   remote_window_ = NULL;
   return false;
 }
 
+// For windows, there is no need to call Create() since the call is made in
+// the constructor but to avoid having more platform specific code in
+// browser_main.cc we tolerate a second call which will do nothing.
 void ProcessSingleton::Create() {
-  DCHECK(!window_);
   DCHECK(!remote_window_);
+  if (window_)
+    return;
+
   HINSTANCE hinst = GetModuleHandle(NULL);
 
   WNDCLASSEX wc = {0};
   wc.cbSize = sizeof(wc);
   wc.lpfnWndProc = ProcessSingleton::WndProcStatic;
   wc.hInstance = hinst;
   wc.lpszClassName = chrome::kMessageWindowClass;
   RegisterClassEx(&wc);
 
   std::wstring user_data_dir;
@@ skipping 99 matching lines @@
   switch (message) {
     case WM_COPYDATA:
       return OnCopyData(reinterpret_cast<HWND>(wparam),
                         reinterpret_cast<COPYDATASTRUCT*>(lparam));
     default:
       break;
   }
 
   return ::DefWindowProc(hwnd, message, wparam, lparam);
 }