Index: content/renderer/device_orientation/device_motion_shared_memory_reader.cc |
diff --git a/content/renderer/device_orientation/device_motion_shared_memory_reader.cc b/content/renderer/device_orientation/device_motion_shared_memory_reader.cc |
new file mode 100644 |
index 0000000000000000000000000000000000000000..510639b85e596f842dc341f0c522ad0aa9031670 |
--- /dev/null |
+++ b/content/renderer/device_orientation/device_motion_shared_memory_reader.cc |
@@ -0,0 +1,82 @@ |
+// Copyright (c) 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 "device_motion_shared_memory_reader.h" |
+ |
+#include "base/debug/trace_event.h" |
+#include "base/metrics/histogram.h" |
+#include "content/common/device_motion_hardware_buffer.h" |
+#include "content/common/device_motion_messages.h" |
+#include "content/public/renderer/render_thread.h" |
+#include "ipc/ipc_sync_message_filter.h" |
+#include "third_party/WebKit/Source/Platform/chromium/public/WebDeviceMotionData.h" |
+ |
+namespace content { |
+ |
+bool DeviceMotionSharedMemoryReader::latestDeviceMotionData( |
+ WebKit::WebDeviceMotionData& data) { |
+ |
+ WebKit::WebDeviceMotionData read_into; |
+ TRACE_EVENT0("DEVICEMOTION", "lastDeviceMotionData"); |
+ |
+ if (!base::SharedMemory::IsHandleValid(renderer_shared_memory_handle_)) |
+ return false; |
+ |
+ // Only try to read this many times before failing to avoid waiting here |
+ // very long in case of contention with the writer. |
+ bool is_ready_for_read = false; |
+ const int kMaximumContentionCount = 10; |
+ int contention_count = -1; |
+ base::subtle::Atomic32 version; |
+ do { |
+ version = device_motion_hardware_buffer_->sequence.ReadBegin(); |
+ is_ready_for_read = device_motion_hardware_buffer_->is_ready_for_read; |
+ memcpy(&read_into, &device_motion_hardware_buffer_->buffer, |
+ sizeof(read_into)); |
+ ++contention_count; |
+ if (contention_count == kMaximumContentionCount) |
+ break; |
+ } while (device_motion_hardware_buffer_->sequence.ReadRetry(version)); |
+ UMA_HISTOGRAM_COUNTS("DeviceMotion.ReadContentionCount", contention_count); |
+ |
+ if (contention_count >= kMaximumContentionCount) { |
+ // We failed to successfully read, presumably because the hardware |
+ // thread was taking unusually long. Don't copy the data to the output |
+ // buffer, and simply leave what was there before. |
+ return false; |
+ } |
+ |
+ // New data was read successfully, copy it into the output buffer. |
+ memcpy(&data, &read_into, sizeof(data)); |
+ |
+ return is_ready_for_read; |
+} |
+ |
+DeviceMotionSharedMemoryReader::DeviceMotionSharedMemoryReader() |
+ : device_motion_hardware_buffer_(NULL) { |
+} |
+ |
+void DeviceMotionSharedMemoryReader::startUpdating() { |
+ CHECK(RenderThread::Get()->Send( |
darin (slow to review)
2013/05/29 06:41:53
are you sure you need to CHECK here?
timvolodine
2013/05/29 18:59:06
hmm, I thought the reasoning for this was that the
|
+ new DeviceMotionHostMsg_StartPolling(&renderer_shared_memory_handle_))); |
darin (slow to review)
2013/05/29 06:41:53
Can you do this using an asynchronous IPC instead?
timvolodine
2013/05/29 18:59:06
I was basing this IPC messaging on how the gamepad
|
+ |
+ bool valid_handle = base::SharedMemory::IsHandleValid( |
+ renderer_shared_memory_handle_); |
+ if (!valid_handle) |
+ return; |
+ renderer_shared_memory_.reset(new base::SharedMemory( |
+ renderer_shared_memory_handle_, true)); |
+ CHECK(renderer_shared_memory_->Map(sizeof(DeviceMotionHardwareBuffer))); |
+ void *memory = renderer_shared_memory_->memory(); |
+ CHECK(memory); |
darin (slow to review)
2013/05/29 06:41:53
i have seen cases where it is difficult to map a l
timvolodine
2013/05/29 18:59:06
I actually borrowed that code from the gamepad imp
|
+ device_motion_hardware_buffer_ = |
+ static_cast<DeviceMotionHardwareBuffer*>(memory); |
+ |
darin (slow to review)
2013/05/29 06:41:53
nit: kill gratuitous new line
timvolodine
2013/05/29 18:59:06
Done.
|
+} |
+ |
+void DeviceMotionSharedMemoryReader::stopUpdating() { |
+ CHECK(RenderThread::Get()->Send(new DeviceMotionHostMsg_StopPolling())); |
darin (slow to review)
2013/05/29 06:41:53
why do you need to CHECK here? this could fail du
timvolodine
2013/05/29 18:59:06
Done. since the StopPolling message is async now (
|
+} |
+ |
+} // namespace content |