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AbstractInterruptibleChannel.java API Doc Java SE 5 API 7945 Fri Aug 26 14:57:10 BST 2005 java.nio.channels.spi

AbstractInterruptibleChannel

java.lang.Object

public abstract class AbstractInterruptibleChannel extends Object implements InterruptibleChannel, Channel

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 {@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 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 {@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 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
version: 1.15, 03/12/19
since: 1.4

Fields Summary
private Object
closeLock
private volatile boolean
open
private Interruptible
interruptor
private volatile boolean
interrupted
private static Method
blockedOnMethod
Constructors Summary
protected AbstractInterruptibleChannel()
Initializes a new instance of this class.
Methods Summary
protected final void begin()
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 try ... finally block as shown above, in order to implement asynchronous closing and interruption for this channel.
if (interruptor == null) { interruptor = new Interruptible() { public void interrupt() { synchronized (closeLock) { if (!open) return; interrupted = true; open = false; try { AbstractInterruptibleChannel.this.implCloseChannel(); } catch (IOException x) { } } }}; } blockedOn(interruptor); if (Thread.currentThread().isInterrupted()) interruptor.interrupt();
static void blockedOn(sun.nio.ch.Interruptible intr)
// package-private if (blockedOnMethod == null) initBlockedOn(); try { blockedOnMethod.invoke(Thread.currentThread(), new Object[] { intr }); } catch (IllegalAccessException x) { throw new Error(x); } catch (IllegalArgumentException x) { throw new Error(x); } catch (InvocationTargetException x) { throw new Error(x); }
public final void close()
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
synchronized (closeLock) { if (!open) return; open = false; implCloseChannel(); }
protected final void end(boolean completed)
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 try ... finally block as shown above, in order to implement asynchronous closing and interruption for this channel.
param
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
throws
ClosedByInterruptException If the thread blocked in the I/O operation was interrupted
blockedOn(null); if (completed) { interrupted = false; return; } if (interrupted) throw new ClosedByInterruptException(); if (!open) throw new AsynchronousCloseException();
protected abstract void 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
private static void initBlockedOn()
AccessController.doPrivileged(new PrivilegedAction() { public Object run() { try { Class th = Class.forName("java.lang.Thread"); blockedOnMethod = th.getDeclaredMethod("blockedOn", new Class[] { Interruptible.class }); blockedOnMethod.setAccessible(true); } catch (ClassNotFoundException x) { throw new Error(x); } catch (NoSuchMethodException x) { throw new Error(x); } catch (IllegalArgumentException x) { throw new Error(x); } catch (ClassCastException x) { throw new Error(x); } return null; }});
public final boolean isOpen()
return open;