Prevent multile DoPoll() calls from being simultaneously pending

content/browser/gamepad/gamepad_provider.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 <cmath>
 #include <set>
 #include <vector>
 
 #include "base/bind.h"
 #include "base/logging.h"
 #include "base/message_loop.h"
 #include "base/threading/thread.h"
 #include "base/threading/thread_restrictions.h"
 #include "content/browser/gamepad/data_fetcher.h"
 #include "content/browser/gamepad/gamepad_provider.h"
 #include "content/browser/gamepad/platform_data_fetcher.h"
 #include "content/common/gamepad_hardware_buffer.h"
 #include "content/common/gamepad_messages.h"
 #include "content/public/browser/browser_thread.h"
 
 namespace content {
 
 GamepadProvider::GamepadProvider()
     : is_paused_(true),
+      have_scheduled_do_poll_(false),
       devices_changed_(true) {
   size_t data_size = sizeof(GamepadHardwareBuffer);
   base::SystemMonitor* monitor = base::SystemMonitor::Get();
   if (monitor)
     monitor->AddDevicesChangedObserver(this);
   bool res = gamepad_shared_memory_.CreateAndMapAnonymous(data_size);
   CHECK(res);
   GamepadHardwareBuffer* hwbuf = SharedMemoryAsHardwareBuffer();
   memset(hwbuf, 0, sizeof(GamepadHardwareBuffer));
 
@@ skipping 76 matching lines @@
 }
 
 void GamepadProvider::SendPauseHint(bool paused) {
   DCHECK(MessageLoop::current() == polling_thread_->message_loop());
   if (data_fetcher_.get())
     data_fetcher_->PauseHint(paused);
 }
 
 void GamepadProvider::DoPoll() {
   DCHECK(MessageLoop::current() == polling_thread_->message_loop());
+  DCHECK(have_scheduled_do_poll_);
+  have_scheduled_do_poll_ = false;
+
   bool changed;
   GamepadHardwareBuffer* hwbuf = SharedMemoryAsHardwareBuffer();
 
   ANNOTATE_BENIGN_RACE_SIZED(
       &hwbuf->buffer,
       sizeof(WebKit::WebGamepads),
       "Racey reads are discarded");
 
   {
     base::AutoLock lock(devices_changed_lock_);
     changed = devices_changed_;
     devices_changed_ = false;
   }
 
   // Acquire the SeqLock. There is only ever one writer to this data.
   // See gamepad_hardware_buffer.h.
   hwbuf->sequence.WriteBegin();
   data_fetcher_->GetGamepadData(&hwbuf->buffer, changed);
   hwbuf->sequence.WriteEnd();
 
   // Schedule our next interval of polling.
   ScheduleDoPoll();
 }
 
 void GamepadProvider::ScheduleDoPoll() {
   DCHECK(MessageLoop::current() == polling_thread_->message_loop());
+  if (have_scheduled_do_poll_)
+    return;
 
   {
     base::AutoLock lock(is_paused_lock_);
     if (is_paused_)
       return;
   }
 
   MessageLoop::current()->PostDelayedTask(
       FROM_HERE,
       base::Bind(&GamepadProvider::DoPoll, Unretained(this)),
       base::TimeDelta::FromMilliseconds(kDesiredSamplingIntervalMs));
+  have_scheduled_do_poll_ = true;
 }
 
 GamepadHardwareBuffer* GamepadProvider::SharedMemoryAsHardwareBuffer() {
   void* mem = gamepad_shared_memory_.memory();
   CHECK(mem);
   return static_cast<GamepadHardwareBuffer*>(mem);
 }
 
 }  // namespace content