java - AsynchronousSocketChannel Read/WritePendingException - 可以同步吗？

Question

我正在开发一个TCP服务器，我很好奇是否可以同步AsynchronousSocketChannel的读取和写入方法。我将 channel 包装到另一个类中，因为我的 channel 需要一些附加功能。我的问题是这是否真的是同步的正确方法:

/**
 * 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);
    }
}

在本例中，writeLock 是一个static final 对象，当我的包装类的任意实例开始写入操作时，它会获取锁。这真的有效还是只是用完了同步块(synchronized block)？

Answer 1

这就是我修复它的方法:

/**
 * 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;
    }
}