src/circular-queue.cc

// Copyright 2010 the V8 project authors. All rights reserved.
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#include "v8.h"

#include "circular-queue-inl.h"

namespace v8 {
namespace internal {


SamplingCircularQueue::SamplingCircularQueue(size_t record_size_in_bytes,
                                             size_t desired_chunk_size_in_bytes,
                                             unsigned buffer_size_in_chunks)
    : record_size_(record_size_in_bytes / sizeof(Cell)),
      chunk_size_in_bytes_(desired_chunk_size_in_bytes / record_size_in_bytes *
                        record_size_in_bytes + sizeof(Cell)),
      chunk_size_(chunk_size_in_bytes_ / sizeof(Cell)),
      buffer_size_(chunk_size_ * buffer_size_in_chunks),
      buffer_(NewArray<Cell>(buffer_size_)) {
  ASSERT(record_size_ * sizeof(Cell) == record_size_in_bytes);
  ASSERT(chunk_size_ * sizeof(Cell) == chunk_size_in_bytes_);
  ASSERT(buffer_size_in_chunks > 2);
  // Mark all chunks as clear.
  for (size_t i = 0; i < buffer_size_; i += chunk_size_) {
    buffer_[i] = kClear;
  }

  // Layout producer and consumer position pointers each on their own
  // cache lines to avoid cache lines thrashing due to simultaneous
  // updates of positions by different processor cores.
  const int positions_size =
      RoundUp(1, kProcessorCacheLineSize) +
      RoundUp(static_cast<int>(sizeof(ProducerPosition)),
              kProcessorCacheLineSize) +
      RoundUp(static_cast<int>(sizeof(ConsumerPosition)),
              kProcessorCacheLineSize);
  positions_ = NewArray<byte>(positions_size);

  producer_pos_ = reinterpret_cast<ProducerPosition*>(
      RoundUp(positions_, kProcessorCacheLineSize));
  producer_pos_->next_chunk_pos = buffer_;
  producer_pos_->enqueue_pos = buffer_;

  consumer_pos_ = reinterpret_cast<ConsumerPosition*>(
      reinterpret_cast<byte*>(producer_pos_) + kProcessorCacheLineSize);
  ASSERT(reinterpret_cast<byte*>(consumer_pos_ + 1) <=
         positions_ + positions_size);
  consumer_pos_->dequeue_chunk_pos = buffer_;
  // The distance ensures that producer and consumer never step on
  // each other's chunks and helps eviction of produced data from
  // the CPU cache (having that chunk size is bigger than the cache.)
  const size_t producer_consumer_distance = (2 * chunk_size_);
  consumer_pos_->dequeue_chunk_poll_pos = buffer_ + producer_consumer_distance;
  consumer_pos_->dequeue_pos = NULL;
}


SamplingCircularQueue::~SamplingCircularQueue() {
  DeleteArray(positions_);
  DeleteArray(buffer_);
}


void* SamplingCircularQueue::StartDequeue() {
  if (consumer_pos_->dequeue_pos != NULL) {
    return consumer_pos_->dequeue_pos;
  } else {
    if (Acquire_Load(consumer_pos_->dequeue_chunk_poll_pos) != kClear) {
      // Skip marker.
      consumer_pos_->dequeue_pos = consumer_pos_->dequeue_chunk_pos + 1;
      consumer_pos_->dequeue_end_pos =
          consumer_pos_->dequeue_chunk_pos + chunk_size_;
      return consumer_pos_->dequeue_pos;
    } else {
      return NULL;
    }
  }
}


void SamplingCircularQueue::FinishDequeue() {
  consumer_pos_->dequeue_pos += record_size_;
  if (consumer_pos_->dequeue_pos < consumer_pos_->dequeue_end_pos) return;
  // Move to next chunk.
  consumer_pos_->dequeue_pos = NULL;
  *consumer_pos_->dequeue_chunk_pos = kClear;
  consumer_pos_->dequeue_chunk_pos += chunk_size_;
  WrapPositionIfNeeded(&consumer_pos_->dequeue_chunk_pos);
  consumer_pos_->dequeue_chunk_poll_pos += chunk_size_;
  WrapPositionIfNeeded(&consumer_pos_->dequeue_chunk_poll_pos);
}


void SamplingCircularQueue::FlushResidualRecords() {
  // Eliminate producer / consumer distance.
  consumer_pos_->dequeue_chunk_poll_pos = consumer_pos_->dequeue_chunk_pos;
}


} }  // namespace v8::internal