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 
11 namespace v8 {
12 namespace 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.
21 template<typename T, unsigned Length>
22 class 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 
V8_ALIGNED(PROCESSOR_CACHE_LINE_SIZE)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