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_messages.h"
  10 #include "content/common/gamepad_user_gesture.h"
  11 #include "content/public/renderer/render_thread.h"
  12 #include "content/common/gamepad_hardware_buffer.h"
  13 #include "ipc/ipc_sync_message_filter.h"
  14
  15 namespace content {
  16
  17 GamepadSharedMemoryReader::GamepadSharedMemoryReader()
  18     : gamepad_hardware_buffer_(NULL),
  19       ever_interacted_with_(false) {
  20   CHECK(RenderThread::Get()->Send(new GamepadHostMsg_StartPolling(
  21       &renderer_shared_memory_handle_)));
  22   // If we don't get a valid handle from the browser, don't try to Map (we're
  23   // probably out of memory or file handles).
  24   bool valid_handle = base::SharedMemory::IsHandleValid(
  25       renderer_shared_memory_handle_);
  26   UMA_HISTOGRAM_BOOLEAN("Gamepad.ValidSharedMemoryHandle", valid_handle);
  27   if (!valid_handle)
  28     return;
  29   renderer_shared_memory_.reset(
  30       new base::SharedMemory(renderer_shared_memory_handle_, true));
  31   CHECK(renderer_shared_memory_->Map(sizeof(GamepadHardwareBuffer)));
  32   void *memory = renderer_shared_memory_->memory();
  33   CHECK(memory);
  34   gamepad_hardware_buffer_ =
  35       static_cast<GamepadHardwareBuffer*>(memory);
  36 }
  37
  38 void GamepadSharedMemoryReader::SampleGamepads(blink::WebGamepads& gamepads) {
  39   // ==========
  40   //   DANGER
  41   // ==========
  42   //
  43   // This logic is duplicated in Pepper as well. If you change it, that also
  44   // needs to be in sync. See ppapi/proxy/gamepad_resource.cc.
  45   blink::WebGamepads read_into;
  46   TRACE_EVENT0("GAMEPAD", "SampleGamepads");
  47
  48   if (!base::SharedMemory::IsHandleValid(renderer_shared_memory_handle_))
  49     return;
  50
  51   // Only try to read this many times before failing to avoid waiting here
  52   // very long in case of contention with the writer. TODO(scottmg) Tune this
  53   // number (as low as 1?) if histogram shows distribution as mostly
  54   // 0-and-maximum.
  55   const int kMaximumContentionCount = 10;
  56   int contention_count = -1;
  57   base::subtle::Atomic32 version;
  58   do {
  59     version = gamepad_hardware_buffer_->sequence.ReadBegin();
  60     memcpy(&read_into, &gamepad_hardware_buffer_->buffer, sizeof(read_into));
  61     ++contention_count;
  62     if (contention_count == kMaximumContentionCount)
  63       break;
  64   } while (gamepad_hardware_buffer_->sequence.ReadRetry(version));
  65   UMA_HISTOGRAM_COUNTS("Gamepad.ReadContentionCount", contention_count);
  66
  67   if (contention_count >= kMaximumContentionCount) {
  68     // We failed to successfully read, presumably because the hardware
  69     // thread was taking unusually long. Don't copy the data to the output
  70     // buffer, and simply leave what was there before.
  71     return;
  72   }
  73
  74   // New data was read successfully, copy it into the output buffer.
  75   memcpy(&gamepads, &read_into, sizeof(gamepads));
  76
  77   if (!ever_interacted_with_) {
  78     if (GamepadsHaveUserGesture(gamepads)) {
  79       ever_interacted_with_ = true;
  80     } else {
  81       // Clear the connected flag if the user hasn't interacted with any of the
  82       // gamepads to prevent fingerprinting. The actual data is not cleared.
  83       // WebKit will only copy out data into the JS buffers for connected
  84       // gamepads so this is sufficient.
  85       for (unsigned i = 0; i < blink::WebGamepads::itemsLengthCap; i++)
  86         gamepads.items[i].connected = false;
  87     }
  88   }
  89 }
  90
  91 GamepadSharedMemoryReader::~GamepadSharedMemoryReader() {
  92   RenderThread::Get()->Send(new GamepadHostMsg_StopPolling());
  93 }
  94
  95 } // namespace content