Fix crash on suspend for chrome os

chrome/browser/chromeos/power/renderer_freezer.cc

 // Copyright 2014 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/chromeos/power/renderer_freezer.h"
 
 #include <cstring>  // needed for strlen()
 
 #include "base/bind.h"
 #include "base/files/file_util.h"
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
 #include "chromeos/dbus/dbus_thread_manager.h"
 
 namespace chromeos {
 
 namespace {
 const char kFreezerStatePath[] =
     "/sys/fs/cgroup/freezer/chrome_renderers/freezer.state";
 const char kFreezeCommand[] = "FROZEN";
 const char kThawCommand[] = "THAWED";
 
 }  // namespace
 
 void RendererFreezer::SuspendImminent() {
+  // SuspendImminent() might end up being called multiple times before we run
+  // OnReadyToSuspend() (crbug.com/414396).  In case a callback is already
+  // pending, we only store the new callback and do nothing else.
+  if (suspend_readiness_callback_.is_null()) {
+    // There is no callback pending so post the task.
+    base::MessageLoop::current()->PostTask(
+        FROM_HERE,
+        base::Bind(&RendererFreezer::OnReadyToSuspend,
+                   weak_factory_.GetWeakPtr()));
+  }
+
+  // Always update the callback because only the most recent one matters.
   suspend_readiness_callback_ = DBusThreadManager::Get()
                                     ->GetPowerManagerClient()
                                     ->GetSuspendReadinessCallback();
-
-  base::MessageLoop::current()->PostTask(
-      FROM_HERE,
-      base::Bind(&RendererFreezer::OnReadyToSuspend,
-                 weak_factory_.GetWeakPtr()));
 }
 
 void RendererFreezer::SuspendDone(const base::TimeDelta& sleep_duration) {
   if (!frozen_)
     return;
 
   if (base::WriteFile(state_path_, kThawCommand, strlen(kThawCommand)) !=
       static_cast<int>(strlen(kThawCommand))) {
     // We failed to write the thaw command and the renderers are still frozen.
     // We are in big trouble because none of the tabs will be responsive so
     // let's crash the browser instead.
     PLOG(FATAL) << "Unable to thaw processes in the cgroup freezer.";
   }
 
   frozen_ = false;
 }
 
 void RendererFreezer::OnReadyToSuspend() {
   if (base::WriteFile(state_path_, kFreezeCommand, strlen(kFreezeCommand)) !=
       static_cast<int>(strlen(kFreezeCommand))) {
     PLOG(WARNING) << "Unable to freeze processes in the cgroup freezer.";
   } else {
     frozen_ = true;
   }
 
-  DCHECK(!suspend_readiness_callback_.is_null());
+  CHECK(!suspend_readiness_callback_.is_null());  // crbug.com/414396
   suspend_readiness_callback_.Run();
   suspend_readiness_callback_.Reset();
 }
 
 RendererFreezer::RendererFreezer()
     : state_path_(base::FilePath(kFreezerStatePath)),
       enabled_(base::PathExists(state_path_) &&
                base::PathIsWritable(state_path_)),
       frozen_(false),
       weak_factory_(this) {
   if (enabled_) {
     DBusThreadManager::Get()->GetPowerManagerClient()->AddObserver(this);
   } else {
     LOG(WARNING) << "Cgroup freezer does not exist or is not writable. "
                  << "Processes will not be frozen during suspend.";
   }
 }
 
 RendererFreezer::~RendererFreezer() {
   if (enabled_)
     DBusThreadManager::Get()->GetPowerManagerClient()->RemoveObserver(this);
 }
 
 }  // namespace chromeos