Implement PollingThread for Device Motion.

content/browser/device_orientation/device_motion_provider.cc

 // Copyright 2013 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 "content/browser/device_orientation/device_motion_provider.h"
 
+#include "base/bind.h"
 #include "base/logging.h"
+#include "base/threading/thread.h"
+#include "base/timer/timer.h"
 #include "content/browser/device_orientation/data_fetcher_shared_memory.h"
 #include "content/common/device_motion_hardware_buffer.h"
 
 namespace content {
 
+namespace {
+const int kPeriodInMilliseconds = 100;
+}
+
+class DeviceMotionProvider::PollingThread : public base::Thread {
+ public:
+  PollingThread(const char* name);

[bulach, 2013/07/24 14:33:27]

nit: explicit

[timvolodine, 2013/07/25 16:46:41]

Done.

+  virtual ~PollingThread();
+
+  void StartPolling(DataFetcherSharedMemory* fetcher,
+      DeviceMotionHardwareBuffer* buffer);

[bulach, 2013/07/24 14:33:27]

nit: left align with the open parens

[timvolodine, 2013/07/25 16:46:41]

Done.

+  void StopPolling();
+
+ private:
+  void DoPoll();

[bulach, 2013/07/24 14:33:27]

nit: add a \n

[timvolodine, 2013/07/25 16:46:41]

Done.

+  scoped_ptr<base::RepeatingTimer<PollingThread> > timer_;
+  DataFetcherSharedMemory* fetcher_;

[bulach, 2013/07/24 14:33:27]

nit:
\n
DISALLOW_COPY_AND_ASSIGN(DeviceMotionProvider::PollingThread);

[timvolodine, 2013/07/25 16:46:41]

Done.

+};
+
+
 DeviceMotionProvider::DeviceMotionProvider()
-    : is_started_(false) {
+    : is_stopped_or_stopping_(true) {
+  Initialize();
+}
+
+DeviceMotionProvider::DeviceMotionProvider(
+    scoped_ptr<DataFetcherSharedMemory> fetcher)
+    : is_stopped_or_stopping_(true) {
+  data_fetcher_.reset(fetcher.release());

[bulach, 2013/07/24 14:33:27]

I think it's possible to:
data_fetcher_ = fetcher;

[timvolodine, 2013/07/25 16:46:41]

that doesn't seem to work because '=' is private apparently. Instead I've
changed this to data_fetcher_ = fetcher.Pass() to better reflect the change of
ownership.

+  Initialize();
+}
+
+DeviceMotionProvider::~DeviceMotionProvider() {
+  // make sure polling thread stops before data_fetcher_ gets deleted.
+  if (polling_thread_)
+    polling_thread_->Stop();
+  data_fetcher_.reset();

[bulach, 2013/07/24 14:33:27]

reset would be called automatically, no?

[timvolodine, 2013/07/25 16:46:41]

yes, but this is a small kind of optimization to make sure data_fetcher is
destroyed asap and is not using CPU resources.

+}
+
+void DeviceMotionProvider::Initialize() {
   size_t data_size = sizeof(DeviceMotionHardwareBuffer);
   bool res = device_motion_shared_memory_.CreateAndMapAnonymous(data_size);
   // TODO(timvolodine): consider not crashing the browser if the check fails.
   CHECK(res);
   DeviceMotionHardwareBuffer* hwbuf = SharedMemoryAsHardwareBuffer();
   memset(hwbuf, 0, sizeof(DeviceMotionHardwareBuffer));
 }
 
-DeviceMotionProvider::~DeviceMotionProvider() {
-}
-
 base::SharedMemoryHandle DeviceMotionProvider::GetSharedMemoryHandleForProcess(
     base::ProcessHandle process) {
   base::SharedMemoryHandle renderer_handle;
   device_motion_shared_memory_.ShareToProcess(process, &renderer_handle);
   return renderer_handle;
 }
 
 void DeviceMotionProvider::StartFetchingDeviceMotionData() {
-  if (is_started_)
+  if (!is_stopped_or_stopping_)

[bulach, 2013/07/24 14:33:27]

would "is_started" be clearer?

[timvolodine, 2013/07/25 16:46:41]

Done.

     return;
+
   if (!data_fetcher_)
     data_fetcher_.reset(new DataFetcherSharedMemory);
-  data_fetcher_->StartFetchingDeviceMotionData(SharedMemoryAsHardwareBuffer());
-  is_started_ = true;
+
+  if (data_fetcher_->NeedsPolling()) {
+    if (!polling_thread_)
+        CreateAndStartPollingThread();
+
+    polling_thread_->message_loop()->PostTask(
+        FROM_HERE,
+        base::Bind(&PollingThread::StartPolling,
+                   base::Unretained(polling_thread_.get()),
+                   data_fetcher_.get(),
+                   SharedMemoryAsHardwareBuffer()));
+  } else {
+    data_fetcher_->StartFetchingDeviceMotionData(
+        SharedMemoryAsHardwareBuffer());
+  }
+
+  is_stopped_or_stopping_ = false;
+}
+
+void DeviceMotionProvider::CreateAndStartPollingThread() {
+  polling_thread_.reset(
+      new PollingThread("Device Motion data polling thread"));

[bulach, 2013/07/24 14:33:27]

nit: perhaps just "DeviceMotion poller" would be enough?

[timvolodine, 2013/07/25 16:46:41]

Done.

+
+  if (!polling_thread_->Start()) {
+      LOG(ERROR) << "Failed to start Device Motion data polling thread";
+      return;
+  }
 }
 
 void DeviceMotionProvider::StopFetchingDeviceMotionData() {
-  if (data_fetcher_)
+  if (is_stopped_or_stopping_)
+    return;
+
+  DCHECK(data_fetcher_);
+
+  if (data_fetcher_->NeedsPolling()) {
+    DCHECK(polling_thread_);
+    polling_thread_->message_loop()->PostTask(
+        FROM_HERE,
+        base::Bind(&PollingThread::StopPolling,
+                   base::Unretained(polling_thread_.get())));
+  } else {
     data_fetcher_->StopFetchingDeviceMotionData();
-  is_started_ = false;
+  }
+
+  is_stopped_or_stopping_ = true;
 }
 
-DeviceMotionHardwareBuffer* DeviceMotionProvider::
-    SharedMemoryAsHardwareBuffer() {
+DeviceMotionHardwareBuffer*
+DeviceMotionProvider::SharedMemoryAsHardwareBuffer() {
   void* mem = device_motion_shared_memory_.memory();
   CHECK(mem);
   return static_cast<DeviceMotionHardwareBuffer*>(mem);
 }
 
+// ---- Polling thread methods

[bulach, 2013/07/24 14:33:27]

nit: probably best to keep this higher up, closer to the declaration.

[timvolodine, 2013/07/25 16:46:41]

Done.

+
+DeviceMotionProvider::PollingThread::PollingThread(const char* name)
+    : base::Thread(name) {
+}
+
+DeviceMotionProvider::PollingThread::~PollingThread() {
+}
+
+void DeviceMotionProvider::PollingThread::StartPolling(
+    DataFetcherSharedMemory* fetcher, DeviceMotionHardwareBuffer* buffer) {
+  DCHECK(base::MessageLoop::current() == message_loop());
+  DCHECK(!timer_);
+
+  fetcher_ = fetcher;
+  fetcher_->StartFetchingDeviceMotionData(buffer);
+  timer_.reset(new base::RepeatingTimer<PollingThread>());
+  timer_->Start(FROM_HERE,
+                base::TimeDelta::FromMilliseconds(kPeriodInMilliseconds),
+                this, &PollingThread::DoPoll);
+}
+
+void DeviceMotionProvider::PollingThread::StopPolling() {
+  DCHECK(base::MessageLoop::current() == message_loop());
+  // this will also stop the timer before killing it.
+  timer_.reset();
+  fetcher_->StopFetchingDeviceMotionData();
+}
+
+void DeviceMotionProvider::PollingThread::DoPoll() {
+  DCHECK(base::MessageLoop::current() == message_loop());
+  fetcher_->FetchDeviceMotionDataIntoBuffer();
+}
+
 }  // namespace content