content/renderer/gamepad_shared_memory_reader.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "content/renderer/gamepad_shared_memory_reader.h"
   6
   7 #include "base/debug/trace_event.h"
   8 #include "base/metrics/histogram.h"
   9 #include "content/common/gamepad_hardware_buffer.h"
  10 #include "content/common/gamepad_user_gesture.h"
  11 #include "content/public/renderer/render_thread.h"
  12 #include "content/renderer/renderer_webkitplatformsupport_impl.h"
  13 #include "ipc/ipc_sync_message_filter.h"
  14 #include "third_party/WebKit/public/platform/WebGamepadListener.h"
  15 #include "third_party/WebKit/public/platform/WebPlatformEventListener.h"
  16
  17 namespace content {
  18
  19 GamepadSharedMemoryReader::GamepadSharedMemoryReader(RenderThread* thread)
  20     : RendererGamepadProvider(thread),
  21       gamepad_hardware_buffer_(NULL),
  22       ever_interacted_with_(false) {
  23 }
  24
  25 void GamepadSharedMemoryReader::SendStartMessage() {
  26   CHECK(RenderThread::Get()->Send(new GamepadHostMsg_StartPolling(
  27       &renderer_shared_memory_handle_)));
  28 }
  29
  30 void GamepadSharedMemoryReader::SendStopMessage() {
  31     RenderThread::Get()->Send(new GamepadHostMsg_StopPolling());
  32 }
  33
  34 void GamepadSharedMemoryReader::Start(
  35     blink::WebPlatformEventListener* listener) {
  36   PlatformEventObserver::Start(listener);
  37
  38   // If we don't get a valid handle from the browser, don't try to Map (we're
  39   // probably out of memory or file handles).
  40   bool valid_handle = base::SharedMemory::IsHandleValid(
  41       renderer_shared_memory_handle_);
  42   UMA_HISTOGRAM_BOOLEAN("Gamepad.ValidSharedMemoryHandle", valid_handle);
  43   if (!valid_handle)
  44     return;
  45
  46   renderer_shared_memory_.reset(
  47       new base::SharedMemory(renderer_shared_memory_handle_, true));
  48   CHECK(renderer_shared_memory_->Map(sizeof(GamepadHardwareBuffer)));
  49   void *memory = renderer_shared_memory_->memory();
  50   CHECK(memory);
  51   gamepad_hardware_buffer_ =
  52       static_cast<GamepadHardwareBuffer*>(memory);
  53 }
  54
  55 void GamepadSharedMemoryReader::SampleGamepads(blink::WebGamepads& gamepads) {
  56   // Blink should have started observing at that point.
  57   CHECK(is_observing());
  58
  59   // ==========
  60   //   DANGER
  61   // ==========
  62   //
  63   // This logic is duplicated in Pepper as well. If you change it, that also
  64   // needs to be in sync. See ppapi/proxy/gamepad_resource.cc.
  65   blink::WebGamepads read_into;
  66   TRACE_EVENT0("GAMEPAD", "SampleGamepads");
  67
  68   if (!base::SharedMemory::IsHandleValid(renderer_shared_memory_handle_))
  69     return;
  70
  71   // Only try to read this many times before failing to avoid waiting here
  72   // very long in case of contention with the writer. TODO(scottmg) Tune this
  73   // number (as low as 1?) if histogram shows distribution as mostly
  74   // 0-and-maximum.
  75   const int kMaximumContentionCount = 10;
  76   int contention_count = -1;
  77   base::subtle::Atomic32 version;
  78   do {
  79     version = gamepad_hardware_buffer_->sequence.ReadBegin();
  80     memcpy(&read_into, &gamepad_hardware_buffer_->buffer, sizeof(read_into));
  81     ++contention_count;
  82     if (contention_count == kMaximumContentionCount)
  83       break;
  84   } while (gamepad_hardware_buffer_->sequence.ReadRetry(version));
  85   UMA_HISTOGRAM_COUNTS("Gamepad.ReadContentionCount", contention_count);
  86
  87   if (contention_count >= kMaximumContentionCount) {
  88     // We failed to successfully read, presumably because the hardware
  89     // thread was taking unusually long. Don't copy the data to the output
  90     // buffer, and simply leave what was there before.
  91     return;
  92   }
  93
  94   // New data was read successfully, copy it into the output buffer.
  95   memcpy(&gamepads, &read_into, sizeof(gamepads));
  96
  97   if (!ever_interacted_with_) {
  98     // Clear the connected flag if the user hasn't interacted with any of the
  99     // gamepads to prevent fingerprinting. The actual data is not cleared.
 100     // WebKit will only copy out data into the JS buffers for connected
 101     // gamepads so this is sufficient.
 102     for (unsigned i = 0; i < blink::WebGamepads::itemsLengthCap; i++)
 103       gamepads.items[i].connected = false;
 104   }
 105 }
 106
 107 GamepadSharedMemoryReader::~GamepadSharedMemoryReader() {
 108 }
 109
 110 bool GamepadSharedMemoryReader::OnControlMessageReceived(
 111     const IPC::Message& message) {
 112   bool handled = true;
 113   IPC_BEGIN_MESSAGE_MAP(GamepadSharedMemoryReader, message)
 114     IPC_MESSAGE_HANDLER(GamepadMsg_GamepadConnected, OnGamepadConnected)
 115     IPC_MESSAGE_HANDLER(GamepadMsg_GamepadDisconnected, OnGamepadDisconnected)
 116     IPC_MESSAGE_UNHANDLED(handled = false)
 117   IPC_END_MESSAGE_MAP()
 118   return handled;
 119 }
 120
 121 void GamepadSharedMemoryReader::OnGamepadConnected(
 122     int index,
 123     const blink::WebGamepad& gamepad) {
 124   // The browser already checks if the user actually interacted with a device.
 125   ever_interacted_with_ = true;
 126
 127   if (listener())
 128     listener()->didConnectGamepad(index, gamepad);
 129 }
 130
 131 void GamepadSharedMemoryReader::OnGamepadDisconnected(
 132     int index,
 133     const blink::WebGamepad& gamepad) {
 134   if (listener())
 135     listener()->didDisconnectGamepad(index, gamepad);
 136 }
 137
 138 } // namespace content