The AsynchronousChannel.java Java example source code
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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:
*
* <ol>
* <li>{@link Future}<V> operation(...)
* <li>void operation(... A attachment, {@link
* CompletionHandler}<V,? super A> handler)</pre>
* </ol>
*
* where <i>operation is the name of the I/O operation (read or write for
* example), <i>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
* <em>state-less {@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 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
*
* <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 that
* prevents further attempts to initiate I/O operations that are <i>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 {@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.
*
* <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;
}
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