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(WebKit::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 WebKit::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 < WebKit::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 96
