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package java.nio.channels.spi;
import java.io.IOException;
import java.nio.channels.AsynchronousCloseException;
import java.nio.channels.Channel;
import java.nio.channels.ClosedByInterruptException;
import java.nio.channels.InterruptibleChannel;
import jdk.internal.access.SharedSecrets;
import sun.nio.ch.Interruptible;
Base implementation class for interruptible channels.
This class encapsulates the low-level machinery required to implement the asynchronous closing and interruption of channels. A concrete channel class must invoke the begin and end methods before and after, respectively, invoking an I/O operation that might block indefinitely. In order to ensure that the end method is always invoked, these methods should be used within a try ... finally block:
boolean completed = false;
try {
begin();
completed = ...; // Perform blocking I/O operation
return ...; // Return result
} finally {
end(completed);
}
The completed argument to the 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 true if, and only if, some bytes were actually transferred into the invoker's target buffer.
A concrete channel class must also implement the 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 end method will throw the appropriate exception.
This class performs the synchronization required to implement the Channel specification. Implementations of the implCloseChannel method need not synchronize against other threads that might be attempting to close the channel.
Author: Mark Reinhold, JSR-51 Expert Group Since: 1.4
/**
* 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
* {@code try} ... {@code finally} block:
*
* <blockquote><pre id="be">
* boolean completed = false;
* try {
* begin();
* completed = ...; // Perform blocking I/O operation
* return ...; // Return result
* } finally {
* end(completed);
* }</pre></blockquote>
*
* <p> 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.
*
* <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 closed;
Initializes a new instance of this class.
/**
* 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 implCloseChannel method in order to complete the close operation.
Throws: - IOException –
If an I/O error occurs
/**
* 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 (closed)
return;
closed = true;
implCloseChannel();
}
}
Closes this channel.
This method is invoked by the 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
/**
* 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 !closed;
}
// -- 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 {@code try} ... {@code finally} block as
* shown <a href="#be">above</a>, 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 (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
begin method, using a try ... finally block as shown above, in order to implement asynchronous
closing and interruption for this channel.
Params: - completed –
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
- ClosedByInterruptException –
If the thread blocked in the I/O operation was interrupted
/**
* 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 {@code try} ... {@code finally} block
* as shown <a href="#be">above</a>, in order to implement asynchronous
* closing and interruption for this channel. </p>
*
* @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.access.SharedSecrets --
static void blockedOn(Interruptible intr) { // package-private
SharedSecrets.getJavaLangAccess().blockedOn(intr);
}
}