Renderer reading side of gamepad

content/browser/gamepad/gamepad_provider.cc

Index: content/browser/gamepad/gamepad_provider.cc
diff --git a/content/browser/gamepad/gamepad_provider.cc b/content/browser/gamepad/gamepad_provider.cc
index 642e2445a7bbe8fa0d0fc8fa7fd1fcbe2827c101..c8eed65a30f00b447a888bfa75eedf7932c9f521 100644
--- a/content/browser/gamepad/gamepad_provider.cc
+++ b/content/browser/gamepad/gamepad_provider.cc
@@ -21,31 +21,29 @@
 #include "content/browser/gamepad/data_fetcher_win.h"
 #endif
 
-namespace gamepad {
+namespace content {
 
-Provider* Provider::instance_ = NULL;
+GamepadProvider* GamepadProvider::instance_ = NULL;
 
-using namespace content;
-
-// Define the default data fetcher that Provider will use if none is supplied.
-// (PlatformDataFetcher).
+// Define the default data fetcher that GamepadProvider will use if none is
+// supplied. (GamepadPlatformDataFetcher).
 #if defined(OS_WIN)
 
-typedef DataFetcherWindows PlatformDataFetcher;
+typedef GamepadDataFetcherWindows GamepadPlatformDataFetcher;
 
 #else
 
-class EmptyDataFetcher : public DataFetcher {
+class GamepadEmptyDataFetcher : public GamepadDataFetcher {
  public:
   void GetGamepadData(WebKit::WebGamepads* pads, bool) {
     pads->length = 0;
   }
 };
-typedef EmptyDataFetcher PlatformDataFetcher;
+typedef GamepadEmptyDataFetcher GamepadPlatformDataFetcher;
 
 #endif
 
-Provider::Provider(DataFetcher* fetcher)
+GamepadProvider::GamepadProvider(GamepadDataFetcher* fetcher)
     : creator_loop_(MessageLoop::current()->message_loop_proxy()),
       provided_fetcher_(fetcher),
       devices_changed_(true),
@@ -59,25 +57,25 @@ Provider::Provider(DataFetcher* fetcher)
   memset(hwbuf, 0, sizeof(GamepadHardwareBuffer));
 }
 
-Provider::~Provider() {
+GamepadProvider::~GamepadProvider() {
   base::SystemMonitor* monitor = base::SystemMonitor::Get();
   if (monitor)
     monitor->RemoveDevicesChangedObserver(this);
   Stop();
 }
 
-base::SharedMemoryHandle Provider::GetRendererSharedMemoryHandle(
+base::SharedMemoryHandle GamepadProvider::GetRendererSharedMemoryHandle(
     base::ProcessHandle process) {
   base::SharedMemoryHandle renderer_handle;
   gamepad_shared_memory_.ShareToProcess(process, &renderer_handle);
   return renderer_handle;
 }
 
-void Provider::OnDevicesChanged() {
+void GamepadProvider::OnDevicesChanged() {
   devices_changed_ = true;
 }
 
-void Provider::Start() {
+void GamepadProvider::Start() {
   DCHECK(MessageLoop::current()->message_loop_proxy() == creator_loop_);
 
   if (polling_thread_.get())
@@ -93,21 +91,21 @@ void Provider::Start() {
   MessageLoop* polling_loop = polling_thread_->message_loop();
   polling_loop->PostTask(
       FROM_HERE,
-      base::Bind(&Provider::DoInitializePollingThread, this));
+      base::Bind(&GamepadProvider::DoInitializePollingThread, this));
 }
 
-void Provider::Stop() {
+void GamepadProvider::Stop() {
   DCHECK(MessageLoop::current()->message_loop_proxy() == creator_loop_);
 
   polling_thread_.reset();
   data_fetcher_.reset();
 }
 
-void Provider::DoInitializePollingThread() {
+void GamepadProvider::DoInitializePollingThread() {
   DCHECK(MessageLoop::current() == polling_thread_->message_loop());
 
   if (!provided_fetcher_.get())
-    provided_fetcher_.reset(new PlatformDataFetcher);
+    provided_fetcher_.reset(new GamepadPlatformDataFetcher);
 
   // Pass ownership of fetcher to provider_.
   data_fetcher_.swap(provided_fetcher_);
@@ -116,30 +114,38 @@ void Provider::DoInitializePollingThread() {
   ScheduleDoPoll();
 }
 
-void Provider::DoPoll() {
+void GamepadProvider::DoPoll() {
   DCHECK(MessageLoop::current() == polling_thread_->message_loop());
   GamepadHardwareBuffer* hwbuf = SharedMemoryAsHardwareBuffer();
-  base::subtle::Barrier_AtomicIncrement(&hwbuf->start_marker, 1);
+
+  ANNOTATE_BENIGN_RACE_SIZED(
+      &hwbuf->buffer,
+      sizeof(WebKit::WebGamepads),
+      "Racey reads are discarded");
+
+  // 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, devices_changed_);
-  base::subtle::Barrier_AtomicIncrement(&hwbuf->end_marker, 1);
+  hwbuf->sequence.WriteEnd();
   devices_changed_ = false;
   // Schedule our next interval of polling.
   ScheduleDoPoll();
 }
 
-void Provider::ScheduleDoPoll() {
+void GamepadProvider::ScheduleDoPoll() {
   DCHECK(MessageLoop::current() == polling_thread_->message_loop());
 
   MessageLoop::current()->PostDelayedTask(
       FROM_HERE,
-      base::Bind(&Provider::DoPoll, weak_factory_.GetWeakPtr()),
+      base::Bind(&GamepadProvider::DoPoll, weak_factory_.GetWeakPtr()),
       kDesiredSamplingIntervalMs);
 }
 
-GamepadHardwareBuffer* Provider::SharedMemoryAsHardwareBuffer() {
+GamepadHardwareBuffer* GamepadProvider::SharedMemoryAsHardwareBuffer() {
   void* mem = gamepad_shared_memory_.memory();
   DCHECK(mem);
   return static_cast<GamepadHardwareBuffer*>(mem);
 }
 
-}  // namespace gamepad
+}  // namespace content