Question

According to this post: https://stackoverflow.com/questions/6666659/threading-implications-of-asynchronousbytechannel the java implementation of asynchronous socket channel doesn’t guarantee that completion handler gets called in a separate thread. So if you are reading into a byte buffer, how do you get notify() called after wait()?

        class CH implements CompletionHandler<Integer,Integer>
       {            
            public volatile int i = 0;
            public void completed(Integer i, Integer o)
            {
               this.i = i;
               synchronized(this)
                {
                    this.notify();
             }
           }

        public void failed(Throwable t, Integer o)
        {
            this.i = -5;                
            synchronized(this)
            {
                this.notify();
            }
        }

    }

               CH x = new CH();
              synchronized (x) {            
                    while (!(x.i == -1 || x.i == -5)) {
                            aschannel.read(bytebuffer, 5, TimeUnit.SECONDS, null, x);
                             x.wait();                                           
                             if(x.i != -1 && x.i != -5){
                                  bytebuffer.flip();
                                   filechannel.write(bytebuffer.array,0,x.i);
                                   bytebuffer.clear();
                               }
               }     


              }

Answer 1

Your program may work, because wait() releases the monitor and allow callbacks to execute.

However, the whole idea of asynchronous I/O is to free the I/O exchange initiator from waiting (and so holding the thread). If you want to wait anyway, then simply use good old synchronous API. Or call read without CompletionHandler, which returns Future, and wait on that Future.