2362N/A * Copyright (c) 2000, 2004, Oracle and/or its affiliates. All rights reserved. 0N/A * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 0N/A * This code is free software; you can redistribute it and/or modify it 0N/A * under the terms of the GNU General Public License version 2 only, as 2362N/A * published by the Free Software Foundation. Oracle designates this 0N/A * particular file as subject to the "Classpath" exception as provided 2362N/A * by Oracle in the LICENSE file that accompanied this code. 0N/A * This code is distributed in the hope that it will be useful, but WITHOUT 0N/A * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 0N/A * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 0N/A * version 2 for more details (a copy is included in the LICENSE file that 0N/A * accompanied this code). 0N/A * You should have received a copy of the GNU General Public License version 0N/A * 2 along with this work; if not, write to the Free Software Foundation, 0N/A * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 2362N/A * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 2362N/A * or visit www.oracle.com if you need additional information or have any 0N/A * A multiplexor of {@link SelectableChannel} objects. 0N/A * <p> A selector may be created by invoking the {@link #open open} method of 0N/A * this class, which will use the system's default {@link 0N/A * java.nio.channels.spi.SelectorProvider </code>selector provider<code>} to 0N/A * create a new selector. A selector may also be created by invoking the 0N/A * {@link java.nio.channels.spi.SelectorProvider#openSelector openSelector} 0N/A * method of a custom selector provider. A selector remains open until it is 0N/A * closed via its {@link #close close} method. 0N/A * <p> A selectable channel's registration with a selector is represented by a 0N/A * {@link SelectionKey} object. A selector maintains three sets of selection 0N/A * <li><p> The <i>key set</i> contains the keys representing the current 0N/A * channel registrations of this selector. This set is returned by the 0N/A * {@link #keys() keys} method. </p></li> 0N/A * <li><p> The <i>selected-key set</i> is the set of keys such that each 0N/A * key's channel was detected to be ready for at least one of the operations 0N/A * identified in the key's interest set during a prior selection operation. 0N/A * This set is returned by the {@link #selectedKeys() selectedKeys} method. 0N/A * The selected-key set is always a subset of the key set. </p></li> 0N/A * <li><p> The <i>cancelled-key</i> set is the set of keys that have been 0N/A * cancelled but whose channels have not yet been deregistered. This set is 0N/A * not directly accessible. The cancelled-key set is always a subset of the 0N/A * key set. </p></li> 0N/A * <p> All three sets are empty in a newly-created selector. 0N/A * <p> A key is added to a selector's key set as a side effect of registering a 0N/A * channel via the channel's {@link SelectableChannel#register(Selector,int) 0N/A * register} method. Cancelled keys are removed from the key set during 0N/A * selection operations. The key set itself is not directly modifiable. 0N/A * <p> A key is added to its selector's cancelled-key set when it is cancelled, 0N/A * whether by closing its channel or by invoking its {@link SelectionKey#cancel 0N/A * cancel} method. Cancelling a key will cause its channel to be deregistered 0N/A * during the next selection operation, at which time the key will removed from 0N/A * all of the selector's key sets. 0N/A * <a name="sks"><p> Keys are added to the selected-key set by selection 0N/A * operations. A key may be removed directly from the selected-key set by 0N/A * invoking the set's {@link java.util.Set#remove(java.lang.Object) remove} 0N/A * method or by invoking the {@link java.util.Iterator#remove() remove} method 0N/A * of an {@link java.util.Iterator </code>iterator<code>} obtained from the 0N/A * set. Keys are never removed from the selected-key set in any other way; 0N/A * they are not, in particular, removed as a side effect of selection 0N/A * operations. Keys may not be added directly to the selected-key set. </p> 0N/A * <h4>Selection</h4> 0N/A * <p> During each selection operation, keys may be added to and removed from a 0N/A * selector's selected-key set and may be removed from its key and 0N/A * cancelled-key sets. Selection is performed by the {@link #select()}, {@link 0N/A * #select(long)}, and {@link #selectNow()} methods, and involves three steps: 0N/A * <li><p> Each key in the cancelled-key set is removed from each key set of 0N/A * which it is a member, and its channel is deregistered. This step leaves 0N/A * the cancelled-key set empty. </p></li> 0N/A * <li><p> The underlying operating system is queried for an update as to the 0N/A * readiness of each remaining channel to perform any of the operations 0N/A * identified by its key's interest set as of the moment that the selection 0N/A * operation began. For a channel that is ready for at least one such 0N/A * operation, one of the following two actions is performed: </p> 0N/A * <li><p> If the channel's key is not already in the selected-key set then 0N/A * it is added to that set and its ready-operation set is modified to 0N/A * identify exactly those operations for which the channel is now reported 0N/A * to be ready. Any readiness information previously recorded in the ready 0N/A * set is discarded. </p></li> 0N/A * <li><p> Otherwise the channel's key is already in the selected-key set, 0N/A * so its ready-operation set is modified to identify any new operations 0N/A * for which the channel is reported to be ready. Any readiness 0N/A * information previously recorded in the ready set is preserved; in other 0N/A * words, the ready set returned by the underlying system is 0N/A * bitwise-disjoined into the key's current ready set. </p></li> 0N/A * If all of the keys in the key set at the start of this step have empty 0N/A * interest sets then neither the selected-key set nor any of the keys' 0N/A * ready-operation sets will be updated. 0N/A * <li><p> If any keys were added to the cancelled-key set while step (2) was 0N/A * in progress then they are processed as in step (1). </p></li> 0N/A * <p> Whether or not a selection operation blocks to wait for one or more 0N/A * channels to become ready, and if so for how long, is the only essential 0N/A * difference between the three selection methods. </p> 0N/A * <h4>Concurrency</h4> 0N/A * <p> Selectors are themselves safe for use by multiple concurrent threads; 0N/A * their key sets, however, are not. 0N/A * <p> The selection operations synchronize on the selector itself, on the key 0N/A * set, and on the selected-key set, in that order. They also synchronize on 0N/A * the cancelled-key set during steps (1) and (3) above. 0N/A * <p> Changes made to the interest sets of a selector's keys while a 0N/A * selection operation is in progress have no effect upon that operation; they 0N/A * will be seen by the next selection operation. 0N/A * <p> Keys may be cancelled and channels may be closed at any time. Hence the 0N/A * presence of a key in one or more of a selector's key sets does not imply 0N/A * that the key is valid or that its channel is open. Application code should 0N/A * be careful to synchronize and check these conditions as necessary if there 0N/A * is any possibility that another thread will cancel a key or close a channel. 0N/A * <p> A thread blocked in one of the {@link #select()} or {@link 0N/A * #select(long)} methods may be interrupted by some other thread in one of 0N/A * <li><p> By invoking the selector's {@link #wakeup wakeup} method, 0N/A * <li><p> By invoking the selector's {@link #close close} method, or 0N/A * <li><p> By invoking the blocked thread's {@link 0N/A * java.lang.Thread#interrupt() interrupt} method, in which case its 0N/A * interrupt status will be set and the selector's {@link #wakeup wakeup} 0N/A * method will be invoked. </p></li> 0N/A * <p> The {@link #close close} method synchronizes on the selector and all 0N/A * three key sets in the same order as in a selection operation. 0N/A * <p> A selector's key and selected-key sets are not, in general, safe for use 0N/A * by multiple concurrent threads. If such a thread might modify one of these 0N/A * sets directly then access should be controlled by synchronizing on the set 0N/A * itself. The iterators returned by these sets' {@link 0N/A * java.util.Set#iterator() iterator} methods are <i>fail-fast:</i> If the set 0N/A * is modified after the iterator is created, in any way except by invoking the 0N/A * iterator's own {@link java.util.Iterator#remove() remove} method, then a 0N/A * {@link java.util.ConcurrentModificationException} will be thrown. </p> 0N/A * @author Mark Reinhold 0N/A * @author JSR-51 Expert Group 0N/A * @see SelectableChannel 0N/A * Initializes a new instance of this class. 0N/A * <p> The new selector is created by invoking the {@link 0N/A * java.nio.channels.spi.SelectorProvider#openSelector openSelector} method 0N/A * of the system-wide default {@link 0N/A * java.nio.channels.spi.SelectorProvider} object. </p> 0N/A * @return A new selector 0N/A * @throws IOException 0N/A * If an I/O error occurs 0N/A * Tells whether or not this selector is open. </p> 0N/A * @return <tt>true</tt> if, and only if, this selector is open 0N/A * Returns the provider that created this channel. </p> 0N/A * @return The provider that created this channel 0N/A * Returns this selector's key set. 0N/A * <p> The key set is not directly modifiable. A key is removed only after 0N/A * it has been cancelled and its channel has been deregistered. Any 0N/A * attempt to modify the key set will cause an {@link 0N/A * UnsupportedOperationException} to be thrown. 0N/A * <p> The key set is <a href="#ksc">not thread-safe</a>. </p> 0N/A * @return This selector's key set 0N/A * @throws ClosedSelectorException 0N/A * If this selector is closed 0N/A * Returns this selector's selected-key set. 0N/A * <p> Keys may be removed from, but not directly added to, the 0N/A * selected-key set. Any attempt to add an object to the key set will 0N/A * cause an {@link UnsupportedOperationException} to be thrown. 0N/A * <p> The selected-key set is <a href="#ksc">not thread-safe</a>. </p> 0N/A * @return This selector's selected-key set 0N/A * @throws ClosedSelectorException 0N/A * If this selector is closed 0N/A * Selects a set of keys whose corresponding channels are ready for I/O 0N/A * <p> This method performs a non-blocking <a href="#selop">selection 0N/A * operation</a>. If no channels have become selectable since the previous 0N/A * selection operation then this method immediately returns zero. 0N/A * <p> Invoking this method clears the effect of any previous invocations 0N/A * of the {@link #wakeup wakeup} method. </p> 0N/A * @return The number of keys, possibly zero, whose ready-operation sets 0N/A * were updated by the selection operation 0N/A * @throws IOException 0N/A * If an I/O error occurs 0N/A * @throws ClosedSelectorException 0N/A * If this selector is closed 0N/A * Selects a set of keys whose corresponding channels are ready for I/O 0N/A * <p> This method performs a blocking <a href="#selop">selection 0N/A * operation</a>. It returns only after at least one channel is selected, 0N/A * this selector's {@link #wakeup wakeup} method is invoked, the current 0N/A * thread is interrupted, or the given timeout period expires, whichever 0N/A * <p> This method does not offer real-time guarantees: It schedules the 0N/A * timeout as if by invoking the {@link Object#wait(long)} method. </p> 0N/A * @param timeout If positive, block for up to <tt>timeout</tt> 0N/A * milliseconds, more or less, while waiting for a 0N/A * channel to become ready; if zero, block indefinitely; 0N/A * must not be negative 0N/A * @return The number of keys, possibly zero, 0N/A * whose ready-operation sets were updated 0N/A * @throws IOException 0N/A * If an I/O error occurs 0N/A * @throws ClosedSelectorException 0N/A * If this selector is closed 0N/A * @throws IllegalArgumentException 0N/A * If the value of the timeout argument is negative 0N/A * Selects a set of keys whose corresponding channels are ready for I/O 0N/A * <p> This method performs a blocking <a href="#selop">selection 0N/A * operation</a>. It returns only after at least one channel is selected, 0N/A * this selector's {@link #wakeup wakeup} method is invoked, or the current 0N/A * thread is interrupted, whichever comes first. </p> 0N/A * @return The number of keys, possibly zero, 0N/A * whose ready-operation sets were updated 0N/A * @throws IOException 0N/A * If an I/O error occurs 0N/A * @throws ClosedSelectorException 0N/A * If this selector is closed 0N/A * Causes the first selection operation that has not yet returned to return 0N/A * <p> If another thread is currently blocked in an invocation of the 0N/A * {@link #select()} or {@link #select(long)} methods then that invocation 0N/A * will return immediately. If no selection operation is currently in 0N/A * progress then the next invocation of one of these methods will return 0N/A * immediately unless the {@link #selectNow()} method is invoked in the 0N/A * meantime. In any case the value returned by that invocation may be 0N/A * non-zero. Subsequent invocations of the {@link #select()} or {@link 0N/A * #select(long)} methods will block as usual unless this method is invoked 0N/A * again in the meantime. 0N/A * <p> Invoking this method more than once between two successive selection 0N/A * operations has the same effect as invoking it just once. </p> 0N/A * @return This selector 0N/A * Closes this selector. 0N/A * <p> If a thread is currently blocked in one of this selector's selection 0N/A * methods then it is interrupted as if by invoking the selector's {@link 0N/A * #wakeup wakeup} method. 0N/A * <p> Any uncancelled keys still associated with this selector are 0N/A * invalidated, their channels are deregistered, and any other resources 0N/A * associated with this selector are released. 0N/A * <p> If this selector is already closed then invoking this method has no 0N/A * <p> After a selector is closed, any further attempt to use it, except by 0N/A * invoking this method or the {@link #wakeup wakeup} method, will cause a 0N/A * {@link ClosedSelectorException} to be thrown. </p> 0N/A * @throws IOException 0N/A * If an I/O error occurs