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/*
* Copyright (C) 2020 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef SRC_PROFILING_PERF_UNWIND_QUEUE_H_
#define SRC_PROFILING_PERF_UNWIND_QUEUE_H_
#include <array>
#include <atomic>
#include "perfetto/base/logging.h"
namespace perfetto {
namespace profiling {
struct WriteView {
bool valid; // if false: buffer is full, and |write_pos| is invalid
uint64_t write_pos;
};
struct ReadView {
uint64_t read_pos;
uint64_t write_pos;
};
// Single-writer, single-reader ring buffer of fixed-size entries (of any
// default-constructible type). Size of the buffer is static for the lifetime of
// UnwindQueue, and must be a power of two.
// Writer side appends entries one at a time, and must stop if there
// is no available capacity.
// Reader side sees all unconsumed entries, and can advance the reader position
// by any amount.
template <typename T, uint32_t QueueSize>
class UnwindQueue {
public:
UnwindQueue() {
static_assert(QueueSize != 0 && ((QueueSize & (QueueSize - 1)) == 0),
"not a power of two");
}
UnwindQueue(const UnwindQueue&) = delete;
UnwindQueue& operator=(const UnwindQueue&) = delete;
UnwindQueue(UnwindQueue&&) = delete;
UnwindQueue& operator=(UnwindQueue&&) = delete;
T& at(uint64_t pos) { return data_[pos % QueueSize]; }
WriteView BeginWrite() {
uint64_t rd = rd_pos_.load(std::memory_order_acquire);
uint64_t wr = wr_pos_.load(std::memory_order_relaxed);
PERFETTO_DCHECK(wr >= rd);
if (wr - rd >= QueueSize)
return WriteView{false, 0}; // buffer fully occupied
return WriteView{true, wr};
}
void CommitWrite() { wr_pos_.fetch_add(1u, std::memory_order_release); }
ReadView BeginRead() {
uint64_t wr = wr_pos_.load(std::memory_order_acquire);
uint64_t rd = rd_pos_.load(std::memory_order_relaxed);
PERFETTO_DCHECK(wr >= rd && wr - rd <= QueueSize);
return ReadView{rd, wr};
}
void CommitNewReadPosition(uint64_t pos) {
rd_pos_.store(pos, std::memory_order_release);
}
private:
std::array<T, QueueSize> data_;
std::atomic<uint64_t> wr_pos_{0};
std::atomic<uint64_t> rd_pos_{0};
};
} // namespace profiling
} // namespace perfetto
#endif // SRC_PROFILING_PERF_UNWIND_QUEUE_H_