AsynchronousSocketChannel Read/WritePendingException - 可以同步吗？

Question

I am working on a TCP Server and I am curious whether it is possible to synchronize the methods read and write of AsynchronousSocketChannel. I wrapped the channel into another class because I needed some additional functionality on my channel. My question is if this is really the right way to synchronize this:

/**
 * writes bytes from a <b>ByteBuffer</b> into an
 * <b>AsynchronousSocketChannel</b>
 * 
 * @param buffer    the ByteBuffer to write from
 * @param onFailure specifies the method that should be called on failure of the
 *                  write operation
 */
public void write(ByteBuffer buffer, final C onFailure) {

    CompletionHandler<Integer, ByteBuffer> handler = new CompletionHandler<Integer, ByteBuffer>() {

        @Override
        public void completed(Integer result, ByteBuffer buf) {
            if (buf.hasRemaining())
                channel.write(buf, buf, this);
        }

        @Override
        public void failed(Throwable exc, ByteBuffer buf) {
            attachment.call(onFailure, exc);
        }

    };

    synchronized (writeLock) {
        this.channel.write(buffer, buffer, handler);
    }
}

In this case writeLock is a static final object that aquires a lock when any of the arbitary instances of my wrapper class starts a write operation. Does this really work or does it just run out of the synchronized block?

Answer 1

This is how I fixed it:

/**
 * writes bytes from a <b>ByteBuffer</b> into an
 * <b>AsynchronousSocketChannel</b>
 * 
 * @param buffer    the ByteBuffer to write from
 * @param onFailure specifies the method that should be called on failure of the
 *                  write operation
 */
public void write(ByteBuffer buffer, final C onFailure) {

    CompletionHandler<Integer, ByteBuffer> handler = new CompletionHandler<Integer, ByteBuffer>() {

        @Override
        public void completed(Integer result, ByteBuffer buf) {
            if (buf.hasRemaining()) {
                channel.write(buf, buf, this);
                return;
            }

            synchronized (writeLock) {
                if (!writeQueue.isEmpty()) {
                    while (writePending)
                        ;

                    ByteBuffer writeBuf = writeQueue.pop();
                    channel.write(writeBuf, writeBuf, this);
                    writePending = true;
                    return;
                }
            }

            writePending = false;
        }

        @Override
        public void failed(Throwable exc, ByteBuffer buf) {
            writePending = false;
            attachment.call(onFailure, exc);
        }

    };

    synchronized (writeLock) {
        while (this.writePending)
            ;

        this.writeQueue.push(buffer);

        ByteBuffer writeBuffer = this.writeQueue.pop();
        this.channel.write(writeBuffer, writeBuffer, handler);
        this.writePending = true;
    }
}