SpscLAQGrowable.java

protected final boolean offerColdPath(final E[] buffer, final long mask, final E e, final long index,
        final long offset) {
  final long lookAheadStep = this.lookAheadStep;
  // normal case, go around the buffer or resize if full (unless we hit max capacity)
  if (lookAheadStep > 0) {
    long lookAheadElementOffset = calcElementOffset(index + lookAheadStep, mask);
    // Try and look ahead a number of elements so we don't have to do this all the time
    if (null == lvElement(buffer, lookAheadElementOffset)) {
      producerBufferLimit = index + lookAheadStep - 1; // joy, there's plenty of room
      writeToQueue(buffer, e, index, offset);
      return true;
    }
    // we're at max capacity, can use up last element
    final int maxCapacity = maxQueueCapacity;
    if (mask + 1 == maxCapacity) {
      if (null == lvElement(buffer, offset)) {
        writeToQueue(buffer, e, index, offset);
        return true;
      }
      // we're full and can't grow
      return false;
    }
    // not at max capacity, so must allow extra slot for JUMP
    if (null == lvElement(buffer, calcElementOffset(index + 1, mask))) { // buffer is not full
      writeToQueue(buffer, e, index, offset);
    } else {
      // allocate new buffer of same length
      final E[] newBuffer = allocate((int) (2*(mask +1) + 1));

      producerBuffer = newBuffer;
      producerMask = newBuffer.length - 2;

      final long offsetInNew = calcElementOffset(index, producerMask);
      linkOldToNew(index, buffer, offset, newBuffer, offsetInNew, e);

      int newCapacity = (int) (producerMask + 1);
      if (newCapacity == maxCapacity) {
        long currConsumerIndex = lvConsumerIndex();
        // use lookAheadStep to store the consumer distance from final buffer
        this.lookAheadStep = -(index - currConsumerIndex);
        producerBufferLimit = currConsumerIndex + maxCapacity - 1;
      } else {
        producerBufferLimit = index + producerMask - 1;
        adjustLookAheadStep(newCapacity);
      }
    }
    return true;
  }
  // the step is negative (or zero) in the period between allocating the max sized buffer and the
  // consumer starting on it
  else {
    final long prevElementsInOtherBuffers = -lookAheadStep;
    // until the consumer starts using the current buffer we need to check consumer index to
    // verify size
    long currConsumerIndex = lvConsumerIndex();
    int size = (int) (index - currConsumerIndex);
    int maxCapacity = (int) mask+1; // we're on max capacity or we wouldn't be here
    if (size == maxCapacity) {
      // consumer index has not changed since adjusting the lookAhead index, we're full
      return false;
    }
    // if consumerIndex progressed enough so that current size indicates it is on same buffer
    long firstIndexInCurrentBuffer = producerBufferLimit - maxCapacity + prevElementsInOtherBuffers;
    if (currConsumerIndex >= firstIndexInCurrentBuffer) {
      // job done, we've now settled into our final state
      adjustLookAheadStep(maxCapacity);
    }
    // consumer is still on some other buffer
    else {
      // how many elements out of buffer?
      this.lookAheadStep = (int) (currConsumerIndex - firstIndexInCurrentBuffer);
    }
    producerBufferLimit = currConsumerIndex + maxCapacity;
    writeToQueue(buffer, e, index, offset);
    return true;
  }
}

private void adjustLookAheadStep(int capacity) {
  lookAheadStep = Math.min(capacity / 4, SpscArrayQueue.MAX_LOOK_AHEAD_STEP);
}