1// Copyright 2010 the V8 project authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#ifndef V8_CIRCULAR_QUEUE_H_
6#define V8_CIRCULAR_QUEUE_H_
7
8#include "src/base/atomicops.h"
9#include "src/globals.h"
10
11namespace v8 {
12namespace internal {
13
14
15// Lock-free cache-friendly sampling circular queue for large
16// records. Intended for fast transfer of large records between a
17// single producer and a single consumer. If the queue is full,
18// StartEnqueue will return NULL. The queue is designed with
19// a goal in mind to evade cache lines thrashing by preventing
20// simultaneous reads and writes to adjanced memory locations.
21template<typename T, unsigned Length>
22class SamplingCircularQueue {
23 public:
24  // Executed on the application thread.
25  SamplingCircularQueue();
26  ~SamplingCircularQueue();
27
28  // StartEnqueue returns a pointer to a memory location for storing the next
29  // record or NULL if all entries are full at the moment.
30  T* StartEnqueue();
31  // Notifies the queue that the producer has complete writing data into the
32  // memory returned by StartEnqueue and it can be passed to the consumer.
33  void FinishEnqueue();
34
35  // Executed on the consumer (analyzer) thread.
36  // Retrieves, but does not remove, the head of this queue, returning NULL
37  // if this queue is empty. After the record had been read by a consumer,
38  // Remove must be called.
39  T* Peek();
40  void Remove();
41
42 private:
43  // Reserved values for the entry marker.
44  enum {
45    kEmpty,  // Marks clean (processed) entries.
46    kFull    // Marks entries already filled by the producer but not yet
47             // completely processed by the consumer.
48  };
49
50  struct V8_ALIGNED(PROCESSOR_CACHE_LINE_SIZE) Entry {
51    Entry() : marker(kEmpty) {}
52    T record;
53    base::Atomic32 marker;
54  };
55
56  Entry* Next(Entry* entry);
57
58  Entry buffer_[Length];
59  V8_ALIGNED(PROCESSOR_CACHE_LINE_SIZE) Entry* enqueue_pos_;
60  V8_ALIGNED(PROCESSOR_CACHE_LINE_SIZE) Entry* dequeue_pos_;
61
62  DISALLOW_COPY_AND_ASSIGN(SamplingCircularQueue);
63};
64
65
66} }  // namespace v8::internal
67
68#endif  // V8_CIRCULAR_QUEUE_H_
69