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// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "third_party/blink/renderer/modules/gamepad/gamepad_shared_memory_reader.h"
#include "base/compiler_specific.h"
#include "base/metrics/histogram_macros.h"
#include "base/task/single_thread_task_runner.h"
#include "base/trace_event/trace_event.h"
#include "device/gamepad/public/cpp/gamepads.h"
#include "device/gamepad/public/mojom/gamepad_hardware_buffer.h"
#include "mojo/public/cpp/bindings/pending_remote.h"
#include "third_party/blink/public/platform/browser_interface_broker_proxy.h"
#include "third_party/blink/renderer/core/frame/local_dom_window.h"
#include "third_party/blink/renderer/modules/gamepad/gamepad_listener.h"
namespace blink {
GamepadSharedMemoryReader::GamepadSharedMemoryReader(LocalDOMWindow& window)
: receiver_(this, &window), gamepad_monitor_remote_(&window) {
// See https://bit.ly/2S0zRAS for task types
scoped_refptr<base::SingleThreadTaskRunner> task_runner =
window.GetTaskRunner(TaskType::kMiscPlatformAPI);
window.GetBrowserInterfaceBroker().GetInterface(
gamepad_monitor_remote_.BindNewPipeAndPassReceiver(task_runner));
gamepad_monitor_remote_->SetObserver(
receiver_.BindNewPipeAndPassRemote(task_runner));
}
void GamepadSharedMemoryReader::Trace(Visitor* visitor) const {
visitor->Trace(receiver_);
visitor->Trace(gamepad_monitor_remote_);
}
void GamepadSharedMemoryReader::SendStartMessage() {
if (gamepad_monitor_remote_.is_bound()) {
gamepad_monitor_remote_->GamepadStartPolling(
&renderer_shared_buffer_region_);
}
}
void GamepadSharedMemoryReader::SendStopMessage() {
if (gamepad_monitor_remote_.is_bound()) {
gamepad_monitor_remote_->GamepadStopPolling();
}
}
void GamepadSharedMemoryReader::Start(blink::GamepadListener* listener) {
DCHECK(!listener_);
listener_ = listener;
SendStartMessage();
// If we don't get a valid handle from the browser, don't try to Map (we're
// probably out of memory or file handles).
bool is_valid = renderer_shared_buffer_region_.IsValid();
UMA_HISTOGRAM_BOOLEAN("Gamepad.ValidSharedMemoryHandle", is_valid);
if (!is_valid)
return;
renderer_shared_buffer_mapping_ = renderer_shared_buffer_region_.Map();
CHECK(renderer_shared_buffer_mapping_.IsValid());
gamepad_hardware_buffer_ = renderer_shared_buffer_mapping_
.GetMemoryAs<device::GamepadHardwareBuffer>();
CHECK(gamepad_hardware_buffer_);
}
void GamepadSharedMemoryReader::Stop() {
DCHECK(listener_);
listener_ = nullptr;
renderer_shared_buffer_region_ = base::ReadOnlySharedMemoryRegion();
renderer_shared_buffer_mapping_ = base::ReadOnlySharedMemoryMapping();
gamepad_hardware_buffer_ = nullptr;
SendStopMessage();
}
void GamepadSharedMemoryReader::SampleGamepads(device::Gamepads* gamepads) {
// Blink should have started observing at this point.
CHECK(listener_);
// ==========
// DANGER
// ==========
//
// This logic is duplicated in Pepper as well. If you change it, that also
// needs to be in sync. See ppapi/proxy/gamepad_resource.cc.
device::Gamepads read_into;
TRACE_EVENT0("GAMEPAD", "SampleGamepads");
if (!renderer_shared_buffer_region_.IsValid())
return;
// Only try to read this many times before failing to avoid waiting here
// very long in case of contention with the writer. TODO(scottmg) Tune this
// number (as low as 1?) if histogram shows distribution as mostly
// 0-and-maximum.
const int kMaximumContentionCount = 10;
int contention_count = -1;
base::subtle::Atomic32 version;
do {
version = gamepad_hardware_buffer_->seqlock.ReadBegin();
UNSAFE_TODO(
memcpy(&read_into, &gamepad_hardware_buffer_->data, sizeof(read_into)));
++contention_count;
if (contention_count == kMaximumContentionCount)
break;
} while (gamepad_hardware_buffer_->seqlock.ReadRetry(version));
UMA_HISTOGRAM_COUNTS_1M("Gamepad.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;
}
// New data was read successfully, copy it into the output buffer.
UNSAFE_TODO(memcpy(gamepads, &read_into, sizeof(*gamepads)));
if (!ever_interacted_with_) {
// Clear the connected flag if the user hasn't interacted with any of the
// gamepads to prevent fingerprinting. The actual data is not cleared.
// WebKit will only copy out data into the JS buffers for connected
// gamepads so this is sufficient.
for (auto& item : gamepads->items) {
item.connected = false;
}
}
}
GamepadSharedMemoryReader::~GamepadSharedMemoryReader() {
if (listener_)
Stop();
}
void GamepadSharedMemoryReader::GamepadConnected(
uint32_t index,
const device::Gamepad& gamepad) {
// The browser already checks if the user actually interacted with a device.
ever_interacted_with_ = true;
if (listener_)
listener_->DidConnectGamepad(index, gamepad);
}
void GamepadSharedMemoryReader::GamepadDisconnected(
uint32_t index,
const device::Gamepad& gamepad) {
if (listener_)
listener_->DidDisconnectGamepad(index, gamepad);
}
} // namespace blink
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