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64 lines
2.0 KiB
C++
64 lines
2.0 KiB
C++
// Copyright (c) 2012 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef GPU_COMMAND_BUFFER_COMMON_COMMAND_BUFFER_SHARED_H_
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#define GPU_COMMAND_BUFFER_COMMON_COMMAND_BUFFER_SHARED_H_
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#include "command_buffer.h"
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#include "base/atomicops.h"
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namespace gpu {
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// This is a standard 4-slot asynchronous communication mechanism, used to
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// ensure that the reader gets a consistent copy of what the writer wrote.
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template<typename T>
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class SharedState {
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T states_[2][2];
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base::subtle::Atomic32 reading_;
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base::subtle::Atomic32 latest_;
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base::subtle::Atomic32 slots_[2];
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public:
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void Initialize() {
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for (int i = 0; i < 2; ++i) {
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for (int j = 0; j < 2; ++j) {
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states_[i][j] = T();
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}
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}
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base::subtle::NoBarrier_Store(&reading_, 0);
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base::subtle::NoBarrier_Store(&latest_, 0);
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base::subtle::NoBarrier_Store(&slots_[0], 0);
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base::subtle::Release_Store(&slots_[1], 0);
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base::subtle::MemoryBarrier();
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}
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void Write(const T& state) {
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int towrite = !base::subtle::Acquire_Load(&reading_);
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int index = !base::subtle::Acquire_Load(&slots_[towrite]);
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states_[towrite][index] = state;
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base::subtle::Release_Store(&slots_[towrite], index);
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base::subtle::Release_Store(&latest_, towrite);
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base::subtle::MemoryBarrier();
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}
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// Attempt to update the state, updating only if the generation counter is
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// newer.
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void Read(T* state) {
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base::subtle::MemoryBarrier();
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int toread = !!base::subtle::Acquire_Load(&latest_);
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base::subtle::Release_Store(&reading_, toread);
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base::subtle::MemoryBarrier();
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int index = !!base::subtle::Acquire_Load(&slots_[toread]);
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if (states_[toread][index].generation - state->generation < 0x80000000U)
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*state = states_[toread][index];
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}
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};
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typedef SharedState<CommandBuffer::State> CommandBufferSharedState;
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} // namespace gpu
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#endif // GPU_COMMAND_BUFFER_COMMON_COMMAND_BUFFER_SHARED_H_
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