This class encapsulates the low-level machinery required to implement * the asynchronous closing and interruption of channels. A concrete channel * class must invoke the {@link #begin begin} and {@link #end end} methods * before and after, respectively, invoking an I/O operation that might block * indefinitely. In order to ensure that the {@link #end end} method is always * invoked, these methods should be used within a * {@code try} ... {@code finally} block: * *
* boolean completed = false;
* try {
* begin();
* completed = ...; // Perform blocking I/O operation
* return ...; // Return result
* } finally {
* end(completed);
* }The {@code completed} argument to the {@link #end end} method tells * whether or not the I/O operation actually completed, that is, whether it had * any effect that would be visible to the invoker. In the case of an * operation that reads bytes, for example, this argument should be * {@code true} if, and only if, some bytes were actually transferred into the * invoker's target buffer. * *
A concrete channel class must also implement the {@link * #implCloseChannel implCloseChannel} method in such a way that if it is * invoked while another thread is blocked in a native I/O operation upon the * channel then that operation will immediately return, either by throwing an * exception or by returning normally. If a thread is interrupted or the * channel upon which it is blocked is asynchronously closed then the channel's * {@link #end end} method will throw the appropriate exception. * *
This class performs the synchronization required to implement the {@link * java.nio.channels.Channel} specification. Implementations of the {@link * #implCloseChannel implCloseChannel} method need not synchronize against * other threads that might be attempting to close the channel.
* * * @author Mark Reinhold * @author JSR-51 Expert Group * @since 1.4 */ public abstract class AbstractInterruptibleChannel implements Channel, InterruptibleChannel { private final Object closeLock = new Object(); private volatile boolean closed; /** * Initializes a new instance of this class. */ protected AbstractInterruptibleChannel() { } /** * Closes this channel. * *If the channel has already been closed then this method returns * immediately. Otherwise it marks the channel as closed and then invokes * the {@link #implCloseChannel implCloseChannel} method in order to * complete the close operation.
* * @throws IOException * If an I/O error occurs */ public final void close() throws IOException { synchronized (closeLock) { if (closed) return; closed = true; implCloseChannel(); } } /** * Closes this channel. * *This method is invoked by the {@link #close close} method in order * to perform the actual work of closing the channel. This method is only * invoked if the channel has not yet been closed, and it is never invoked * more than once. * *
An implementation of this method must arrange for any other thread * that is blocked in an I/O operation upon this channel to return * immediately, either by throwing an exception or by returning normally. *
* * @throws IOException * If an I/O error occurs while closing the channel */ protected abstract void implCloseChannel() throws IOException; public final boolean isOpen() { return !closed; } // -- Interruption machinery -- private Interruptible interruptor; private volatile Thread interrupted; /** * Marks the beginning of an I/O operation that might block indefinitely. * *This method should be invoked in tandem with the {@link #end end} * method, using a {@code try} ... {@code finally} block as * shown above, in order to implement asynchronous * closing and interruption for this channel.
*/ protected final void begin() { if (interruptor == null) { interruptor = new Interruptible() { public void interrupt(Thread target) { synchronized (closeLock) { if (closed) return; closed = true; interrupted = target; try { AbstractInterruptibleChannel.this.implCloseChannel(); } catch (IOException x) { } } }}; } blockedOn(interruptor); Thread me = Thread.currentThread(); if (me.isInterrupted()) interruptor.interrupt(me); } /** * Marks the end of an I/O operation that might block indefinitely. * *This method should be invoked in tandem with the {@link #begin * begin} method, using a {@code try} ... {@code finally} block * as shown above, in order to implement asynchronous * closing and interruption for this channel.
* * @param completed * {@code true} if, and only if, the I/O operation completed * successfully, that is, had some effect that would be visible to * the operation's invoker * * @throws AsynchronousCloseException * If the channel was asynchronously closed * * @throws ClosedByInterruptException * If the thread blocked in the I/O operation was interrupted */ protected final void end(boolean completed) throws AsynchronousCloseException { blockedOn(null); Thread interrupted = this.interrupted; if (interrupted != null && interrupted == Thread.currentThread()) { this.interrupted = null; throw new ClosedByInterruptException(); } if (!completed && closed) throw new AsynchronousCloseException(); } // -- jdk.internal.misc.SharedSecrets -- static void blockedOn(Interruptible intr) { // package-private SharedSecrets.getJavaLangAccess().blockedOn(Thread.currentThread(), intr); } }