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 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
