Revert 146792 - Lock-free GamepadSeqLock (try 2)

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"
@@ skipping 103 matching lines @@
   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());
   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.
-  WebKit::WebGamepads tmp;
-  data_fetcher_->GetGamepadData(&tmp, changed);
-  hwbuf->gamepads.Write(tmp);
+  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());
 
   {
     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));
 }
 
 GamepadHardwareBuffer* GamepadProvider::SharedMemoryAsHardwareBuffer() {
   void* mem = gamepad_shared_memory_.memory();
   CHECK(mem);
   return static_cast<GamepadHardwareBuffer*>(mem);
 }
 
 }  // namespace content