LinkedTransferQueue是阻塞队列还是非阻塞队列？

Question

I read about concurrent queue in java, and i received confusion about LinkedTransferQueue. What is type of LinkedTransferQueue (is it blocking or not-blocking queue)? I have read that LinkedTransferQueue uses a CAS (compare and swap) approach and park method from Unsafe, and consists from nodes and pointers like ConcurrentLinkedQueue, it pushed on idea that it's a non-blocking queue. But interface TransferQueue extends BlockingQueue . It looks ambiguous. In the end, is LinkedTransferQueue blocking or not-blocking queue?

Answer 1

The LinkedTransferQueue is an unbounded queue so though it is BlockingQueue it will never actually reach the common producer/consumer patterns normal BlockingQueue implementations may achieve.

So, is it or isn't it blocking? It actually depends on the operation. For example, a few are listed below.

Non-blocking operations:

• offer
• put
• add
• poll
• tryTransfer

Blocking operations:

• take
• transfer

Point is, if an operation can achieve without blocking it will. Since the LinkedTransferQueue is forced to be unbounded, it can get away with both blocking and non-blocking operations.

If interested, I found this out by going through the Java 8 implementation.

Answer 2

From the Javadoc :

An optionally-bounded blocking queue based on linked nodes.