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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 "ppapi/proxy/gamepad_resource.h"
#include <string.h>
#include "base/bind.h"
#include "base/threading/platform_thread.h"
#include "ppapi/proxy/dispatch_reply_message.h"
#include "ppapi/proxy/ppapi_messages.h"
#include "ppapi/shared_impl/ppb_gamepad_shared.h"
namespace ppapi {
namespace proxy {
namespace {
// This is the read logic from content/common/gamepad_seqlock.h
base::subtle::Atomic32 ReadBegin(const base::subtle::Atomic32* sequence) {
base::subtle::Atomic32 version;
for (;;) {
version = base::subtle::NoBarrier_Load(sequence);
// If the counter is even, then the associated data might be in a
// consistent state, so we can try to read.
if ((version & 1) == 0)
break;
// Otherwise, the writer is in the middle of an update. Retry the read.
base::PlatformThread::YieldCurrentThread();
}
return version;
}
bool ReadRetry(const base::subtle::Atomic32* sequence,
base::subtle::Atomic32 version) {
// If the sequence number was updated then a read should be re-attempted.
// -- Load fence, read membarrier
return base::subtle::Release_Load(sequence) != version;
}
} // namespace
GamepadResource::GamepadResource(Connection connection, PP_Instance instance)
: PluginResource(connection, instance),
buffer_(NULL) {
memset(&last_read_, 0, sizeof(last_read_));
SendCreateToBrowser(PpapiHostMsg_Gamepad_Create());
CallBrowser<PpapiPluginMsg_Gamepad_SendMemory>(
PpapiHostMsg_Gamepad_RequestMemory(),
base::Bind(&GamepadResource::OnPluginMsgSendMemory, this));
}
GamepadResource::~GamepadResource() {
}
void GamepadResource::Sample(PP_GamepadsSampleData* data) {
if (!buffer_) {
// Browser hasn't sent back our shared memory, give the plugin gamepad
// data corresponding to "not connected".
memset(data, 0, sizeof(PP_GamepadsSampleData));
return;
}
// ==========
// DANGER
// ==========
//
// This logic is duplicated in the renderer as well. If you change it, that
// also needs to be in sync. See gamepad_shared_memory_reader.cc.
// Only try to read this many times before failing to avoid waiting here
// very long in case of contention with the writer.
const int kMaximumContentionCount = 10;
int contention_count = -1;
base::subtle::Atomic32 version;
WebKitGamepads read_into;
do {
version = ReadBegin(&buffer_->sequence);
memcpy(&read_into, &buffer_->buffer, sizeof(read_into));
++contention_count;
if (contention_count == kMaximumContentionCount)
break;
} while (ReadRetry(&buffer_->sequence, version));
// In the event of a read failure, just leave the last read data as-is (the
// hardware thread is taking unusally long).
if (contention_count < kMaximumContentionCount)
ConvertWebKitGamepadData(read_into, &last_read_);
memcpy(data, &last_read_, sizeof(PP_GamepadsSampleData));
}
void GamepadResource::OnPluginMsgSendMemory(
const ResourceMessageReplyParams& params) {
// On failure, the handle will be null and the CHECK below will be tripped.
base::SharedMemoryHandle handle;
params.GetSharedMemoryHandleAtIndex(0, &handle);
shared_memory_.reset(new base::SharedMemory(handle, true));
CHECK(shared_memory_->Map(sizeof(ContentGamepadHardwareBuffer)));
buffer_ = static_cast<const ContentGamepadHardwareBuffer*>(
shared_memory_->memory());
}
} // namespace proxy
} // namespace ppapi
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