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// 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 "content/renderer/gamepad_shared_memory_reader.h"
#include "base/debug/trace_event.h"
#include "base/metrics/histogram.h"
#include "content/common/gamepad_messages.h"
#include "content/common/gamepad_user_gesture.h"
#include "content/public/renderer/render_thread.h"
#include "content/common/gamepad_hardware_buffer.h"
#include "ipc/ipc_sync_message_filter.h"
namespace content {
GamepadSharedMemoryReader::GamepadSharedMemoryReader()
: gamepad_hardware_buffer_(NULL),
ever_interacted_with_(false) {
CHECK(RenderThread::Get()->Send(new GamepadHostMsg_StartPolling(
&renderer_shared_memory_handle_)));
// 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 valid_handle = base::SharedMemory::IsHandleValid(
renderer_shared_memory_handle_);
UMA_HISTOGRAM_BOOLEAN("Gamepad.ValidSharedMemoryHandle", valid_handle);
if (!valid_handle)
return;
renderer_shared_memory_.reset(
new base::SharedMemory(renderer_shared_memory_handle_, true));
CHECK(renderer_shared_memory_->Map(sizeof(GamepadHardwareBuffer)));
void *memory = renderer_shared_memory_->memory();
CHECK(memory);
gamepad_hardware_buffer_ =
static_cast<GamepadHardwareBuffer*>(memory);
}
void GamepadSharedMemoryReader::SampleGamepads(WebKit::WebGamepads& gamepads) {
// ==========
// 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.
WebKit::WebGamepads read_into;
TRACE_EVENT0("GAMEPAD", "SampleGamepads");
if (!base::SharedMemory::IsHandleValid(renderer_shared_memory_handle_))
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_->sequence.ReadBegin();
memcpy(&read_into, &gamepad_hardware_buffer_->buffer, sizeof(read_into));
++contention_count;
if (contention_count == kMaximumContentionCount)
break;
} while (gamepad_hardware_buffer_->sequence.ReadRetry(version));
UMA_HISTOGRAM_COUNTS("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.
memcpy(&gamepads, &read_into, sizeof(gamepads));
if (!ever_interacted_with_) {
if (GamepadsHaveUserGesture(gamepads)) {
ever_interacted_with_ = true;
} else {
// 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 (unsigned i = 0; i < WebKit::WebGamepads::itemsLengthCap; i++)
gamepads.items[i].connected = false;
}
}
}
GamepadSharedMemoryReader::~GamepadSharedMemoryReader() {
RenderThread::Get()->Send(new GamepadHostMsg_StopPolling());
}
} // namespace content
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