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// Copyright 2010 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_PROFILER_CIRCULAR_QUEUE_H_
#define V8_PROFILER_CIRCULAR_QUEUE_H_
#include "src/base/atomicops.h"
#include "src/common/globals.h"
namespace v8 {
namespace internal {
// Lock-free cache-friendly sampling circular queue for large
// records. Intended for fast transfer of large records between a
// single producer and a single consumer. If the queue is full,
// StartEnqueue will return nullptr. The queue is designed with
// a goal in mind to evade cache lines thrashing by preventing
// simultaneous reads and writes to adjanced memory locations.
template<typename T, unsigned Length>
class SamplingCircularQueue {
public:
// Executed on the application thread.
SamplingCircularQueue();
~SamplingCircularQueue();
SamplingCircularQueue(const SamplingCircularQueue&) = delete;
SamplingCircularQueue& operator=(const SamplingCircularQueue&) = delete;
// StartEnqueue returns a pointer to a memory location for storing the next
// record or nullptr if all entries are full at the moment.
T* StartEnqueue();
// Notifies the queue that the producer has complete writing data into the
// memory returned by StartEnqueue and it can be passed to the consumer.
void FinishEnqueue();
// Executed on the consumer (analyzer) thread.
// Retrieves, but does not remove, the head of this queue, returning nullptr
// if this queue is empty. After the record had been read by a consumer,
// Remove must be called.
T* Peek();
void Remove();
private:
// Reserved values for the entry marker.
enum {
kEmpty, // Marks clean (processed) entries.
kFull // Marks entries already filled by the producer but not yet
// completely processed by the consumer.
};
struct alignas(PROCESSOR_CACHE_LINE_SIZE) Entry {
Entry() : marker(kEmpty) {}
T record;
base::Atomic32 marker;
};
Entry* Next(Entry* entry);
Entry buffer_[Length];
alignas(PROCESSOR_CACHE_LINE_SIZE) Entry* enqueue_pos_;
alignas(PROCESSOR_CACHE_LINE_SIZE) Entry* dequeue_pos_;
};
} // namespace internal
} // namespace v8
#endif // V8_PROFILER_CIRCULAR_QUEUE_H_
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