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_PROFILER_CIRCULAR_QUEUE_H_ 6 #define V8_PROFILER_CIRCULAR_QUEUE_H_ 7 8 #include "src/base/atomicops.h" 9 #include "src/common/globals.h" 10 11 namespace v8 { 12 namespace internal { 13 14 // Lock-free cache-friendly sampling circular queue for large 15 // records. Intended for fast transfer of large records between a 16 // single producer and a single consumer. If the queue is full, 17 // StartEnqueue will return nullptr. The queue is designed with 18 // a goal in mind to evade cache lines thrashing by preventing 19 // simultaneous reads and writes to adjanced memory locations. 20 template<typename T, unsigned Length> 21 class SamplingCircularQueue { 22 public: 23 // Executed on the application thread. 24 SamplingCircularQueue(); 25 ~SamplingCircularQueue(); 26 SamplingCircularQueue(const SamplingCircularQueue&) = delete; 27 SamplingCircularQueue& operator=(const SamplingCircularQueue&) = delete; 28 29 // StartEnqueue returns a pointer to a memory location for storing the next 30 // record or nullptr if all entries are full at the moment. 31 T* StartEnqueue(); 32 // Notifies the queue that the producer has complete writing data into the 33 // memory returned by StartEnqueue and it can be passed to the consumer. 34 void FinishEnqueue(); 35 36 // Executed on the consumer (analyzer) thread. 37 // Retrieves, but does not remove, the head of this queue, returning nullptr 38 // if this queue is empty. After the record had been read by a consumer, 39 // Remove must be called. 40 T* Peek(); 41 void Remove(); 42 43 private: 44 // Reserved values for the entry marker. 45 enum { 46 kEmpty, // Marks clean (processed) entries. 47 kFull // Marks entries already filled by the producer but not yet 48 // completely processed by the consumer. 49 }; 50 51 struct alignas(PROCESSOR_CACHE_LINE_SIZE) Entry { EntryEntry52 Entry() : marker(kEmpty) {} 53 T record; 54 base::Atomic32 marker; 55 }; 56 57 Entry* Next(Entry* entry); 58 59 Entry buffer_[Length]; 60 alignas(PROCESSOR_CACHE_LINE_SIZE) Entry* enqueue_pos_; 61 alignas(PROCESSOR_CACHE_LINE_SIZE) Entry* dequeue_pos_; 62 }; 63 64 65 } // namespace internal 66 } // namespace v8 67 68 #endif // V8_PROFILER_CIRCULAR_QUEUE_H_ 69