// Copyright 2010 the V8 project 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 V8_PROFILER_CIRCULAR_QUEUE_H_
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#define V8_PROFILER_CIRCULAR_QUEUE_H_
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#include "src/base/atomicops.h"
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#include "src/globals.h"
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namespace v8 {
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namespace internal {
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// Lock-free cache-friendly sampling circular queue for large
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// records. Intended for fast transfer of large records between a
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// single producer and a single consumer. If the queue is full,
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// StartEnqueue will return nullptr. The queue is designed with
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// a goal in mind to evade cache lines thrashing by preventing
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// simultaneous reads and writes to adjanced memory locations.
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template<typename T, unsigned Length>
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class SamplingCircularQueue {
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public:
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// Executed on the application thread.
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SamplingCircularQueue();
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~SamplingCircularQueue();
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// StartEnqueue returns a pointer to a memory location for storing the next
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// record or nullptr if all entries are full at the moment.
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T* StartEnqueue();
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// Notifies the queue that the producer has complete writing data into the
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// memory returned by StartEnqueue and it can be passed to the consumer.
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void FinishEnqueue();
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// Executed on the consumer (analyzer) thread.
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// Retrieves, but does not remove, the head of this queue, returning nullptr
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// if this queue is empty. After the record had been read by a consumer,
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// Remove must be called.
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T* Peek();
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void Remove();
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private:
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// Reserved values for the entry marker.
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enum {
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kEmpty, // Marks clean (processed) entries.
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kFull // Marks entries already filled by the producer but not yet
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// completely processed by the consumer.
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};
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struct V8_ALIGNED(PROCESSOR_CACHE_LINE_SIZE) Entry {
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Entry() : marker(kEmpty) {}
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T record;
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base::Atomic32 marker;
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};
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Entry* Next(Entry* entry);
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Entry buffer_[Length];
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V8_ALIGNED(PROCESSOR_CACHE_LINE_SIZE) Entry* enqueue_pos_;
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V8_ALIGNED(PROCESSOR_CACHE_LINE_SIZE) Entry* dequeue_pos_;
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DISALLOW_COPY_AND_ASSIGN(SamplingCircularQueue);
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};
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} // namespace internal
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} // namespace v8
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#endif // V8_PROFILER_CIRCULAR_QUEUE_H_
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