AbstractInterruptibleChannel

public abstract class AbstractInterruptibleChannel extends Object
implements Channel InterruptibleChannel
Known Direct Subclasses
Known Indirect Subclasses

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.

Protected Constructor Summary

AbstractInterruptibleChannel()
Initializes a new instance of this class.

Public Method Summary

final void
close()
Closes this channel.
final boolean
isOpen()
Tells whether or not this channel is open.

Protected Method Summary

final void
begin()
Marks the beginning of an I/O operation that might block indefinitely.
final void
end(boolean completed)
Marks the end of an I/O operation that might block indefinitely.
abstract void
implCloseChannel()
Closes this channel.

Inherited Method Summary

Protected Constructors

protected AbstractInterruptibleChannel ()

Initializes a new instance of this class.

Public Methods

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 implCloseChannel method in order to complete the close operation.

Throws
IOException If an I/O error occurs

public final boolean isOpen ()

Tells whether or not this channel is open.

Returns
  • true if, and only if, this channel is open

Protected Methods

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 end method, using a try ... finally block as shown above, in order to implement asynchronous closing and interruption for this channel.

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 begin method, using a try ... finally block as shown above, in order to implement asynchronous closing and interruption for this channel.

Parameters
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

protected abstract void 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