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package java.nio.channels;
import java.io.IOException;
import java.util.concurrent.Future; // javadoc
A channel that supports asynchronous I/O operations. Asynchronous I/O
operations will usually take one of two forms:
Future<V> operation(...)
void operation(... A attachment, CompletionHandler<V,? super A> handler)
where operation is the name of the I/O operation (read or write for
example), V is the result type of the I/O operation, and A is
the type of an object attached to the I/O operation to provide context when
consuming the result. The attachment is important for cases where a
state-less CompletionHandler is used to consume the result of many I/O operations. In the first form, the methods defined by the Future interface may be used to check if the operation has completed, wait for its completion, and to retrieve the result. In the second form, a CompletionHandler is invoked to consume the result of the I/O operation when it completes or fails.
A channel that implements this interface is asynchronously
closeable: If an I/O operation is outstanding on the channel and the channel's close method is invoked, then the I/O operation fails with the exception AsynchronousCloseException.
Asynchronous channels are safe for use by multiple concurrent threads.
Some channel implementations may support concurrent reading and writing, but
may not allow more than one read and one write operation to be outstanding at
any given time.
Cancellation
The Future interface defines the cancel method to cancel execution. This causes all threads waiting on the result of the I/O operation to throw CancellationException. Whether the underlying I/O operation can be cancelled is highly implementation specific and therefore not specified. Where cancellation leaves the channel, or the entity to which it is connected, in an inconsistent state, then the channel is put into an implementation specific error state that
prevents further attempts to initiate I/O operations that are similar to the operation that was cancelled. For example, if a read operation is cancelled but the implementation cannot guarantee that bytes have not been read from the channel then it puts the channel into an error state; further attempts to initiate a read operation cause an unspecified runtime exception to be thrown. Similarly, if a write operation is cancelled but the implementation cannot guarantee that bytes have not been written to the channel then subsequent attempts to initiate a write will fail with an unspecified runtime exception.
Where the cancel method is invoked with the
mayInterruptIfRunning parameter set to true then the I/O operation may be interrupted by closing the channel. In that case all threads waiting on the result of the I/O operation throw CancellationException and any other I/O operations outstanding on the channel complete with the exception AsynchronousCloseException.
Where the cancel method is invoked to cancel read or write operations then it is recommended that all buffers used in the I/O operations be discarded or care taken to ensure that the buffers are not accessed while the channel remains open. @since 1.7
/**
* A channel that supports asynchronous I/O operations. Asynchronous I/O
* operations will usually take one of two forms:
*
* <ol>
* <li><pre>{@link Future}<V> <em>operation</em>(<em>...</em>)</pre></li>
* <li><pre>void <em>operation</em>(<em>...</em> A attachment, {@link
* CompletionHandler}<V,? super A> handler)</pre></li>
* </ol>
*
* where <i>operation</i> is the name of the I/O operation (read or write for
* example), <i>V</i> is the result type of the I/O operation, and <i>A</i> is
* the type of an object attached to the I/O operation to provide context when
* consuming the result. The attachment is important for cases where a
* <em>state-less</em> {@code CompletionHandler} is used to consume the result
* of many I/O operations.
*
* <p> In the first form, the methods defined by the {@link Future Future}
* interface may be used to check if the operation has completed, wait for its
* completion, and to retrieve the result. In the second form, a {@link
* CompletionHandler} is invoked to consume the result of the I/O operation when
* it completes or fails.
*
* <p> A channel that implements this interface is <em>asynchronously
* closeable</em>: If an I/O operation is outstanding on the channel and the
* channel's {@link #close close} method is invoked, then the I/O operation
* fails with the exception {@link AsynchronousCloseException}.
*
* <p> Asynchronous channels are safe for use by multiple concurrent threads.
* Some channel implementations may support concurrent reading and writing, but
* may not allow more than one read and one write operation to be outstanding at
* any given time.
*
* <h2>Cancellation</h2>
*
* <p> The {@code Future} interface defines the {@link Future#cancel cancel}
* method to cancel execution. This causes all threads waiting on the result of
* the I/O operation to throw {@link java.util.concurrent.CancellationException}.
* Whether the underlying I/O operation can be cancelled is highly implementation
* specific and therefore not specified. Where cancellation leaves the channel,
* or the entity to which it is connected, in an inconsistent state, then the
* channel is put into an implementation specific <em>error state</em> that
* prevents further attempts to initiate I/O operations that are <i>similar</i>
* to the operation that was cancelled. For example, if a read operation is
* cancelled but the implementation cannot guarantee that bytes have not been
* read from the channel then it puts the channel into an error state; further
* attempts to initiate a {@code read} operation cause an unspecified runtime
* exception to be thrown. Similarly, if a write operation is cancelled but the
* implementation cannot guarantee that bytes have not been written to the
* channel then subsequent attempts to initiate a {@code write} will fail with
* an unspecified runtime exception.
*
* <p> Where the {@link Future#cancel cancel} method is invoked with the {@code
* mayInterruptIfRunning} parameter set to {@code true} then the I/O operation
* may be interrupted by closing the channel. In that case all threads waiting
* on the result of the I/O operation throw {@code CancellationException} and
* any other I/O operations outstanding on the channel complete with the
* exception {@link AsynchronousCloseException}.
*
* <p> Where the {@code cancel} method is invoked to cancel read or write
* operations then it is recommended that all buffers used in the I/O operations
* be discarded or care taken to ensure that the buffers are not accessed while
* the channel remains open.
*
* @since 1.7
*/
public interface AsynchronousChannel
extends Channel
{
Closes this channel.
Any outstanding asynchronous operations upon this channel will complete with the exception AsynchronousCloseException. After a channel is closed, further attempts to initiate asynchronous I/O operations complete immediately with cause ClosedChannelException.
This method otherwise behaves exactly as specified by the Channel interface.
Throws: - IOException –
If an I/O error occurs
/**
* Closes this channel.
*
* <p> Any outstanding asynchronous operations upon this channel will
* complete with the exception {@link AsynchronousCloseException}. After a
* channel is closed, further attempts to initiate asynchronous I/O
* operations complete immediately with cause {@link ClosedChannelException}.
*
* <p> This method otherwise behaves exactly as specified by the {@link
* Channel} interface.
*
* @throws IOException
* If an I/O error occurs
*/
@Override
void close() throws IOException;
}