1 /* 2 * Copyright (c) 2007, 2013, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package java.nio.channels; 27 28 import java.io.IOException; 29 import java.util.concurrent.Future; // javadoc 30 31 /** 32 * A channel that supports asynchronous I/O operations. Asynchronous I/O 33 * operations will usually take one of two forms: 34 * 35 * <ol> 36 * <li><pre>{@link Future}<V> <em>operation</em>(<em>...</em>)</pre></li> 37 * <li><pre>void <em>operation</em>(<em>...</em> A attachment, {@link 38 * CompletionHandler}<V,? super A> handler)</pre></li> 39 * </ol> 40 * 41 * where <i>operation</i> is the name of the I/O operation (read or write for 42 * example), <i>V</i> is the result type of the I/O operation, and <i>A</i> is 43 * the type of an object attached to the I/O operation to provide context when 44 * consuming the result. The attachment is important for cases where a 45 * <em>state-less</em> {@code CompletionHandler} is used to consume the result 46 * of many I/O operations. 47 * 48 * <p> In the first form, the methods defined by the {@link Future Future} 49 * interface may be used to check if the operation has completed, wait for its 50 * completion, and to retrieve the result. In the second form, a {@link 51 * CompletionHandler} is invoked to consume the result of the I/O operation when 52 * it completes or fails. 53 * 54 * <p> A channel that implements this interface is <em>asynchronously 55 * closeable</em>: If an I/O operation is outstanding on the channel and the 56 * channel's {@link #close close} method is invoked, then the I/O operation 57 * fails with the exception {@link AsynchronousCloseException}. 58 * 59 * <p> Asynchronous channels are safe for use by multiple concurrent threads. 60 * Some channel implementations may support concurrent reading and writing, but 61 * may not allow more than one read and one write operation to be outstanding at 62 * any given time. 63 * 64 * <h2>Cancellation</h2> 65 * 66 * <p> The {@code Future} interface defines the {@link Future#cancel cancel} 67 * method to cancel execution. This causes all threads waiting on the result of 68 * the I/O operation to throw {@link java.util.concurrent.CancellationException}. 69 * Whether the underlying I/O operation can be cancelled is highly implementation 70 * specific and therefore not specified. Where cancellation leaves the channel, 71 * or the entity to which it is connected, in an inconsistent state, then the 72 * channel is put into an implementation specific <em>error state</em> that 73 * prevents further attempts to initiate I/O operations that are <i>similar</i> 74 * to the operation that was cancelled. For example, if a read operation is 75 * cancelled but the implementation cannot guarantee that bytes have not been 76 * read from the channel then it puts the channel into an error state; further 77 * attempts to initiate a {@code read} operation cause an unspecified runtime 78 * exception to be thrown. Similarly, if a write operation is cancelled but the 79 * implementation cannot guarantee that bytes have not been written to the 80 * channel then subsequent attempts to initiate a {@code write} will fail with 81 * an unspecified runtime exception. 82 * 83 * <p> Where the {@link Future#cancel cancel} method is invoked with the {@code 84 * mayInterruptIfRunning} parameter set to {@code true} then the I/O operation 85 * may be interrupted by closing the channel. In that case all threads waiting 86 * on the result of the I/O operation throw {@code CancellationException} and 87 * any other I/O operations outstanding on the channel complete with the 88 * exception {@link AsynchronousCloseException}. 89 * 90 * <p> Where the {@code cancel} method is invoked to cancel read or write 91 * operations then it is recommended that all buffers used in the I/O operations 92 * be discarded or care taken to ensure that the buffers are not accessed while 93 * the channel remains open. 94 * 95 * @since 1.7 96 */ 97 98 public interface AsynchronousChannel 99 extends Channel 100 { 101 /** 102 * Closes this channel. 103 * 104 * <p> Any outstanding asynchronous operations upon this channel will 105 * complete with the exception {@link AsynchronousCloseException}. After a 106 * channel is closed, further attempts to initiate asynchronous I/O 107 * operations complete immediately with cause {@link ClosedChannelException}. 108 * 109 * <p> This method otherwise behaves exactly as specified by the {@link 110 * Channel} interface. 111 * 112 * @throws IOException 113 * If an I/O error occurs 114 */ 115 @Override close()116 void close() throws IOException; 117 } 118