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
GamepadSharedMemoryReader()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
SampleGamepads(blink::WebGamepads & gamepads)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
~GamepadSharedMemoryReader()91 GamepadSharedMemoryReader::~GamepadSharedMemoryReader() {
92 RenderThread::Get()->Send(new GamepadHostMsg_StopPolling());
93 }
94
95 } // namespace content
96