AsynchronousSocketChannel still throws unspecified exception (original) (raw)

Alan Bateman Alan.Bateman at oracle.com
Wed Jul 13 10:34:47 PDT 2011

cowwoc wrote:

: Okay, but this contradicts our original discussion and how j.u.c works (which we're trying to be consistent with). I'll give you a simple example. If I invoke CountDownLatch.await(0, TimeUnit.MILLISECONDS) the specification reads "If the current count is zero then this method returns immediately." So first of all we've established that a timeout of zero should never block. This is a wait timeout, meaning that CountDownLatch.await will block/wait when a timeout is specified (assuming the latch hasn't counted down). So if this were a synchronous I/O API then all would be clear.

With an asynchronous I/O API then the read/write methods never block/wait. The timeout is instead associated with the I/O operation to support error handling in the event that the peer does not respond. The

0 case should be clear, the <= 0 is less clear and is currently specified (and implemented) to work like the read/write methods that doesn't have timeout parameters. Translating this into synchronous terms then it's equivalent to await().

Reading the "available bytes" requires reading from the socket so a read will be initiated. If it completes before the timeout has elapsed then the timer will be cancelled. I understand but I expect this to work similar to ReentrantLock.tryLock(0, TimeUnit). If available() >= 0 then it should return all available bytes immediately regardless of what the timeout value is. I believe you simply need to invoke available() before beginning a read. If it returns a non-zero value, disable the timeout and read forever (the OS guarantees this should return instantaneously). For socket I/O (AsynchronousSocketChannel) this would be expensive. I think what we need to establish is whether this is really needed, and if so, what is the API. Possible API approaches would be a channel mode (configureImmediateMode/equivalent), new readNow/writeNow methods, or even an "available" method.

-Alan.

More information about the nio-dev mailing list