The AbstractInterruptibleChannel.java Java example source code
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* accompanied this code).
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/*
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package java.nio.channels.spi;
import java.io.IOException;
import java.lang.reflect.Method;
import java.lang.reflect.InvocationTargetException;
import java.nio.channels.*;
import java.security.AccessController;
import java.security.PrivilegedAction;
import sun.nio.ch.Interruptible;
/**
* Base implementation class for interruptible channels.
*
* <p> 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
* <tt>try ... finally block:
*
* <blockquote> * boolean completed = false;
* try {
* begin();
* completed = ...; // Perform blocking I/O operation
* return ...; // Return result
* } finally {
* end(completed);
* }</pre>
*
* <p> The 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
* <tt>true if, and only if, some bytes were actually transferred into the
* invoker's target buffer.
*
* <p> 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.
*
* <p> 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. </p>
*
*
* @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 open = true;
/**
* Initializes a new instance of this class.
*/
protected AbstractInterruptibleChannel() { }
/**
* Closes this channel.
*
* <p> 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. </p>
*
* @throws IOException
* If an I/O error occurs
*/
public final void close() throws IOException {
synchronized (closeLock) {
if (!open)
return;
open = false;
implCloseChannel();
}
}
/**
* Closes this channel.
*
* <p> 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.
*
* <p> 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.
* </p>
*
* @throws IOException
* If an I/O error occurs while closing the channel
*/
protected abstract void implCloseChannel() throws IOException;
public final boolean isOpen() {
return open;
}
// -- Interruption machinery --
private Interruptible interruptor;
private volatile Thread interrupted;
/**
* Marks the beginning of an I/O operation that might block indefinitely.
*
* <p> This method should be invoked in tandem with the {@link #end end}
* method, using a <tt>try ... finally block as
* shown <a href="#be">above, in order to implement asynchronous
* closing and interruption for this channel. </p>
*/
protected final void begin() {
if (interruptor == null) {
interruptor = new Interruptible() {
public void interrupt(Thread target) {
synchronized (closeLock) {
if (!open)
return;
open = false;
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.
*
* <p> This method should be invoked in tandem with the {@link #begin
* begin} method, using a <tt>try ... finally block
* as shown <a href="#be">above, in order to implement asynchronous
* closing and interruption for this channel. </p>
*
* @param completed
* <tt>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()) {
interrupted = null;
throw new ClosedByInterruptException();
}
if (!completed && !open)
throw new AsynchronousCloseException();
}
// -- sun.misc.SharedSecrets --
static void blockedOn(Interruptible intr) { // package-private
sun.misc.SharedSecrets.getJavaLangAccess().blockedOn(Thread.currentThread(),
intr);
}
}
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