如何解决java7 nio socket WritePendingException？

Question

java doc said it will occurred when do write operate by former wirte not complete.

Unchecked exception thrown when an attempt is made to write to an asynchronous socket channel and a previous write has not completed.

a simple code to describe this stage:

  sendMsg(data: ByteBuffer): Future[Unit] = {
    val p = Promise[Unit]
    this.synchronized {
      //socketChannel: AsynchronousSocketChannel is connected socket
      socketChannel.write(data, 1, new CompletionHandler[Integer, Int] {
        override def completed(result: Integer, attachment: Int): Unit = {
          p.trySuccess(Unit)
        }

        override def failed(exc: Throwable, attachment: Int): Unit = {
          p.tryFailure(exc)
        }
      }
    }
    p.future
  }

I attempt to lock write operation until it completed with this unwork code:

val writeLock = new ReentrantLock

def sendMsg(data: ByteBuffer) = {
  val p = Promise[Unit]

  writeLock.lock()

  socketChannel.write(data, 1, new CompletionHandler[Integer, Int] {
    override def completed(result: Integer, attachment: Int): Unit = {
      writeLock.unlock()

      p.trySuccess(Unit)
    }

    override def failed(exc: Throwable, attachment: Int): Unit = {
      p.tryFailure(exc)
      writeLock.unlock()
    }
  })
  p.future
}

but it throw IllegalMonitorStateException exception.
Hope some help to to run it concurrently. Besides, I have another question, why not java sdk deal with it.It seems I should wait a async operation complete.Thanks

Answer 1

Is not that Java should handle this, because if it would you would be loosing control over your code.

You don't have to "wait". You write your data, and "invalidate" the client for writing. When the write is completed (that's why you have such method), you re-validate the client for writting.

The key concept is that, when selecting channels to write, you skip those that are "invalid" at that momment.

I made a nio async io implementation few years ago, you might take a look to get further hints

https://github.com/NadirRoGue/asyncnetworkengine/tree/master/src/org/mmocore/network

Take a look specifically at MMOClient.sendPacket() WriteHandler.completed()