root/src/circular-queue.h
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#ifndef V8_CIRCULAR_QUEUE_H_
#define V8_CIRCULAR_QUEUE_H_
namespace v8 {
namespace internal {
// Lock-free cache-friendly sampling circular queue for large
// records. Intended for fast transfer of large records between a
// single producer and a single consumer. If the queue is full,
// previous unread records are overwritten. The queue is designed with
// a goal in mind to evade cache lines thrashing by preventing
// simultaneous reads and writes to adjanced memory locations.
//
// IMPORTANT: as a producer never checks for chunks cleanness, it is
// possible that it can catch up and overwrite a chunk that a consumer
// is currently reading, resulting in a corrupt record being read.
class SamplingCircularQueue {
public:
// Executed on the application thread.
SamplingCircularQueue(int record_size_in_bytes,
int desired_chunk_size_in_bytes,
int buffer_size_in_chunks);
~SamplingCircularQueue();
// Enqueue returns a pointer to a memory location for storing the next
// record.
INLINE(void* Enqueue());
// Executed on the consumer (analyzer) thread.
// StartDequeue returns a pointer to a memory location for retrieving
// the next record. After the record had been read by a consumer,
// FinishDequeue must be called. Until that moment, subsequent calls
// to StartDequeue will return the same pointer.
void* StartDequeue();
void FinishDequeue();
// Due to a presence of slipping between the producer and the consumer,
// the queue must be notified whether producing has been finished in order
// to process remaining records from the buffer.
void FlushResidualRecords();
typedef AtomicWord Cell;
// Reserved values for the first cell of a record.
static const Cell kClear = 0; // Marks clean (processed) chunks.
static const Cell kEnd = -1; // Marks the end of the buffer.
private:
struct ProducerPosition {
Cell* enqueue_pos;
};
struct ConsumerPosition {
Cell* dequeue_chunk_pos;
Cell* dequeue_chunk_poll_pos;
Cell* dequeue_pos;
Cell* dequeue_end_pos;
};
INLINE(void WrapPositionIfNeeded(Cell** pos));
const int record_size_;
const int chunk_size_in_bytes_;
const int chunk_size_;
const int buffer_size_;
const int producer_consumer_distance_;
Cell* buffer_;
byte* positions_;
ProducerPosition* producer_pos_;
ConsumerPosition* consumer_pos_;
DISALLOW_COPY_AND_ASSIGN(SamplingCircularQueue);
};
} } // namespace v8::internal
#endif // V8_CIRCULAR_QUEUE_H_