| /* |
| * Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| package java.nio.channels; |
| |
| import java.io.Closeable; |
| import java.io.IOException; |
| import java.nio.channels.spi.SelectorProvider; |
| import java.util.Objects; |
| import java.util.Set; |
| import java.util.function.Consumer; |
| |
| |
| /** |
| * A multiplexor of {@link SelectableChannel} objects. |
| * |
| * <p> A selector may be created by invoking the {@link #open open} method of |
| * this class, which will use the system's default {@link |
| * java.nio.channels.spi.SelectorProvider selector provider} to |
| * create a new selector. A selector may also be created by invoking the |
| * {@link java.nio.channels.spi.SelectorProvider#openSelector openSelector} |
| * method of a custom selector provider. A selector remains open until it is |
| * closed via its {@link #close close} method. |
| * |
| * <a id="ks"></a> |
| * |
| * <p> A selectable channel's registration with a selector is represented by a |
| * {@link SelectionKey} object. A selector maintains three sets of selection |
| * keys: |
| * |
| * <ul> |
| * |
| * <li><p> The <i>key set</i> contains the keys representing the current |
| * channel registrations of this selector. This set is returned by the |
| * {@link #keys() keys} method. </p></li> |
| * |
| * <li><p> The <i>selected-key set</i> is the set of keys such that each |
| * key's channel was detected to be ready for at least one of the operations |
| * identified in the key's interest set during a prior selection operation |
| * that adds keys or updates keys in the set. |
| * This set is returned by the {@link #selectedKeys() selectedKeys} method. |
| * The selected-key set is always a subset of the key set. </p></li> |
| * |
| * <li><p> The <i>cancelled-key</i> set is the set of keys that have been |
| * cancelled but whose channels have not yet been deregistered. This set is |
| * not directly accessible. The cancelled-key set is always a subset of the |
| * key set. </p></li> |
| * |
| * </ul> |
| * |
| * <p> All three sets are empty in a newly-created selector. |
| * |
| * <p> A key is added to a selector's key set as a side effect of registering a |
| * channel via the channel's {@link SelectableChannel#register(Selector,int) |
| * register} method. Cancelled keys are removed from the key set during |
| * selection operations. The key set itself is not directly modifiable. |
| * |
| * <p> A key is added to its selector's cancelled-key set when it is cancelled, |
| * whether by closing its channel or by invoking its {@link SelectionKey#cancel |
| * cancel} method. Cancelling a key will cause its channel to be deregistered |
| * during the next selection operation, at which time the key will be removed |
| * from all of the selector's key sets. |
| * |
| * <a id="sks"></a><p> Keys are added to the selected-key set by selection |
| * operations. A key may be removed directly from the selected-key set by |
| * invoking the set's {@link java.util.Set#remove(java.lang.Object) remove} |
| * method or by invoking the {@link java.util.Iterator#remove() remove} method |
| * of an {@link java.util.Iterator iterator} obtained from the set. |
| * All keys may be removed from the selected-key set by invoking the set's |
| * {@link java.util.Set#clear() clear} method. Keys may not be added directly |
| * to the selected-key set. </p> |
| * |
| * <a id="selop"></a> |
| * <h2>Selection</h2> |
| * |
| * <p> A selection operation queries the underlying operating system for an |
| * update as to the readiness of each registered channel to perform any of the |
| * operations identified by its key's interest set. There are two forms of |
| * selection operation: |
| * |
| * <ol> |
| * |
| * <li><p> The {@link #select()}, {@link #select(long)}, and {@link #selectNow()} |
| * methods add the keys of channels ready to perform an operation to the |
| * selected-key set, or update the ready-operation set of keys already in the |
| * selected-key set. </p></li> |
| * |
| * <li><p> The {@link #select(Consumer)}, {@link #select(Consumer, long)}, and |
| * {@link #selectNow(Consumer)} methods perform an <i>action</i> on the key |
| * of each channel that is ready to perform an operation. These methods do |
| * not add to the selected-key set. </p></li> |
| * |
| * </ol> |
| * |
| * <h3>Selection operations that add to the selected-key set</h3> |
| * |
| * <p> During each selection operation, keys may be added to and removed from a |
| * selector's selected-key set and may be removed from its key and |
| * cancelled-key sets. Selection is performed by the {@link #select()}, {@link |
| * #select(long)}, and {@link #selectNow()} methods, and involves three steps: |
| * </p> |
| * |
| * <ol> |
| * |
| * <li><p> Each key in the cancelled-key set is removed from each key set of |
| * which it is a member, and its channel is deregistered. This step leaves |
| * the cancelled-key set empty. </p></li> |
| * |
| * <li><p> The underlying operating system is queried for an update as to the |
| * readiness of each remaining channel to perform any of the operations |
| * identified by its key's interest set as of the moment that the selection |
| * operation began. For a channel that is ready for at least one such |
| * operation, one of the following two actions is performed: </p> |
| * |
| * <ol> |
| * |
| * <li><p> If the channel's key is not already in the selected-key set then |
| * it is added to that set and its ready-operation set is modified to |
| * identify exactly those operations for which the channel is now reported |
| * to be ready. Any readiness information previously recorded in the ready |
| * set is discarded. </p></li> |
| * |
| * <li><p> Otherwise the channel's key is already in the selected-key set, |
| * so its ready-operation set is modified to identify any new operations |
| * for which the channel is reported to be ready. Any readiness |
| * information previously recorded in the ready set is preserved; in other |
| * words, the ready set returned by the underlying system is |
| * bitwise-disjoined into the key's current ready set. </p></li> |
| * |
| * </ol> |
| * |
| * If all of the keys in the key set at the start of this step have empty |
| * interest sets then neither the selected-key set nor any of the keys' |
| * ready-operation sets will be updated. |
| * |
| * <li><p> If any keys were added to the cancelled-key set while step (2) was |
| * in progress then they are processed as in step (1). </p></li> |
| * |
| * </ol> |
| * |
| * <p> Whether or not a selection operation blocks to wait for one or more |
| * channels to become ready, and if so for how long, is the only essential |
| * difference between the three selection methods. </p> |
| * |
| * |
| * <h3>Selection operations that perform an action on selected keys</h3> |
| * |
| * <p> During each selection operation, keys may be removed from the selector's |
| * key, selected-key, and cancelled-key sets. Selection is performed by the |
| * {@link #select(Consumer)}, {@link #select(Consumer,long)}, and {@link |
| * #selectNow(Consumer)} methods, and involves three steps: </p> |
| * |
| * <ol> |
| * |
| * <li><p> Each key in the cancelled-key set is removed from each key set of |
| * which it is a member, and its channel is deregistered. This step leaves |
| * the cancelled-key set empty. </p></li> |
| * |
| * <li><p> The underlying operating system is queried for an update as to the |
| * readiness of each remaining channel to perform any of the operations |
| * identified by its key's interest set as of the moment that the selection |
| * operation began. |
| * |
| * <p> For a channel that is ready for at least one such operation, the |
| * ready-operation set of the channel's key is set to identify exactly the |
| * operations for which the channel is ready and the <i>action</i> specified |
| * to the {@code select} method is invoked to consume the channel's key. Any |
| * readiness information previously recorded in the ready set is discarded |
| * prior to invoking the <i>action</i>. |
| * |
| * <p> Alternatively, where a channel is ready for more than one operation, |
| * the <i>action</i> may be invoked more than once with the channel's key and |
| * ready-operation set modified to a subset of the operations for which the |
| * channel is ready. Where the <i>action</i> is invoked more than once for |
| * the same key then its ready-operation set never contains operation bits |
| * that were contained in the set at previous calls to the <i>action</i> |
| * in the same selection operation. </p></li> |
| * |
| * <li><p> If any keys were added to the cancelled-key set while step (2) was |
| * in progress then they are processed as in step (1). </p></li> |
| * |
| * </ol> |
| * |
| * |
| * <h2>Concurrency</h2> |
| * |
| * <p> A Selector and its key set are safe for use by multiple concurrent |
| * threads. Its selected-key set and cancelled-key set, however, are not. |
| * |
| * <p> The selection operations synchronize on the selector itself, on the |
| * selected-key set, in that order. They also synchronize on the cancelled-key |
| * set during steps (1) and (3) above. |
| * |
| * <p> Changes made to the interest sets of a selector's keys while a |
| * selection operation is in progress have no effect upon that operation; they |
| * will be seen by the next selection operation. |
| * |
| * <p> Keys may be cancelled and channels may be closed at any time. Hence the |
| * presence of a key in one or more of a selector's key sets does not imply |
| * that the key is valid or that its channel is open. Application code should |
| * be careful to synchronize and check these conditions as necessary if there |
| * is any possibility that another thread will cancel a key or close a channel. |
| * |
| * <p> A thread blocked in a selection operation may be interrupted by some |
| * other thread in one of three ways: |
| * |
| * <ul> |
| * |
| * <li><p> By invoking the selector's {@link #wakeup wakeup} method, |
| * </p></li> |
| * |
| * <li><p> By invoking the selector's {@link #close close} method, or |
| * </p></li> |
| * |
| * <li><p> By invoking the blocked thread's {@link |
| * java.lang.Thread#interrupt() interrupt} method, in which case its |
| * interrupt status will be set and the selector's {@link #wakeup wakeup} |
| * method will be invoked. </p></li> |
| * |
| * </ul> |
| * |
| * <p> The {@link #close close} method synchronizes on the selector and its |
| * selected-key set in the same order as in a selection operation. |
| * |
| * <a id="ksc"></a> |
| * <p> A Selector's key set is safe for use by multiple concurrent threads. |
| * Retrieval operations from the key set do not generally block and so may |
| * overlap with new registrations that add to the set, or with the cancellation |
| * steps of selection operations that remove keys from the set. Iterators and |
| * spliterators return elements reflecting the state of the set at some point at |
| * or since the creation of the iterator/spliterator. They do not throw |
| * {@link java.util.ConcurrentModificationException ConcurrentModificationException}. |
| * |
| * <a id="sksc"></a> |
| * <p> A selector's selected-key set is not, in general, safe for use by |
| * multiple concurrent threads. If such a thread might modify the set directly |
| * then access should be controlled by synchronizing on the set itself. The |
| * iterators returned by the set's {@link java.util.Set#iterator() iterator} |
| * methods are <i>fail-fast:</i> If the set is modified after the iterator is |
| * created, in any way except by invoking the iterator's own {@link |
| * java.util.Iterator#remove() remove} method, then a {@link |
| * java.util.ConcurrentModificationException} will be thrown. </p> |
| * |
| * @author Mark Reinhold |
| * @author JSR-51 Expert Group |
| * @since 1.4 |
| * |
| * @see SelectableChannel |
| * @see SelectionKey |
| */ |
| |
| public abstract class Selector implements Closeable { |
| |
| /** |
| * Initializes a new instance of this class. |
| */ |
| protected Selector() { } |
| |
| /** |
| * Opens a selector. |
| * |
| * <p> The new selector is created by invoking the {@link |
| * java.nio.channels.spi.SelectorProvider#openSelector openSelector} method |
| * of the system-wide default {@link |
| * java.nio.channels.spi.SelectorProvider} object. </p> |
| * |
| * @return A new selector |
| * |
| * @throws IOException |
| * If an I/O error occurs |
| */ |
| public static Selector open() throws IOException { |
| return SelectorProvider.provider().openSelector(); |
| } |
| |
| /** |
| * Tells whether or not this selector is open. |
| * |
| * @return {@code true} if, and only if, this selector is open |
| */ |
| public abstract boolean isOpen(); |
| |
| /** |
| * Returns the provider that created this channel. |
| * |
| * @return The provider that created this channel |
| */ |
| public abstract SelectorProvider provider(); |
| |
| /** |
| * Returns this selector's key set. |
| * |
| * <p> The key set is not directly modifiable. A key is removed only after |
| * it has been cancelled and its channel has been deregistered. Any |
| * attempt to modify the key set will cause an {@link |
| * UnsupportedOperationException} to be thrown. |
| * |
| * <p> The set is <a href="#ksc">safe</a> for use by multiple concurrent |
| * threads. </p> |
| * |
| * @return This selector's key set |
| * |
| * @throws ClosedSelectorException |
| * If this selector is closed |
| */ |
| public abstract Set<SelectionKey> keys(); |
| |
| /** |
| * Returns this selector's selected-key set. |
| * |
| * <p> Keys may be removed from, but not directly added to, the |
| * selected-key set. Any attempt to add an object to the key set will |
| * cause an {@link UnsupportedOperationException} to be thrown. |
| * |
| * <p> The selected-key set is <a href="#sksc">not thread-safe</a>. </p> |
| * |
| * @return This selector's selected-key set |
| * |
| * @throws ClosedSelectorException |
| * If this selector is closed |
| */ |
| public abstract Set<SelectionKey> selectedKeys(); |
| |
| /** |
| * Selects a set of keys whose corresponding channels are ready for I/O |
| * operations. |
| * |
| * <p> This method performs a non-blocking <a href="#selop">selection |
| * operation</a>. If no channels have become selectable since the previous |
| * selection operation then this method immediately returns zero. |
| * |
| * <p> Invoking this method clears the effect of any previous invocations |
| * of the {@link #wakeup wakeup} method. </p> |
| * |
| * @return The number of keys, possibly zero, whose ready-operation sets |
| * were updated by the selection operation |
| * |
| * @throws IOException |
| * If an I/O error occurs |
| * |
| * @throws ClosedSelectorException |
| * If this selector is closed |
| */ |
| public abstract int selectNow() throws IOException; |
| |
| /** |
| * Selects a set of keys whose corresponding channels are ready for I/O |
| * operations. |
| * |
| * <p> This method performs a blocking <a href="#selop">selection |
| * operation</a>. It returns only after at least one channel is selected, |
| * this selector's {@link #wakeup wakeup} method is invoked, the current |
| * thread is interrupted, or the given timeout period expires, whichever |
| * comes first. |
| * |
| * <p> This method does not offer real-time guarantees: It schedules the |
| * timeout as if by invoking the {@link Object#wait(long)} method. </p> |
| * |
| * @param timeout If positive, block for up to {@code timeout} |
| * milliseconds, more or less, while waiting for a |
| * channel to become ready; if zero, block indefinitely; |
| * must not be negative |
| * |
| * @return The number of keys, possibly zero, |
| * whose ready-operation sets were updated |
| * |
| * @throws IOException |
| * If an I/O error occurs |
| * |
| * @throws ClosedSelectorException |
| * If this selector is closed |
| * |
| * @throws IllegalArgumentException |
| * If the value of the timeout argument is negative |
| */ |
| public abstract int select(long timeout) throws IOException; |
| |
| /** |
| * Selects a set of keys whose corresponding channels are ready for I/O |
| * operations. |
| * |
| * <p> This method performs a blocking <a href="#selop">selection |
| * operation</a>. It returns only after at least one channel is selected, |
| * this selector's {@link #wakeup wakeup} method is invoked, or the current |
| * thread is interrupted, whichever comes first. </p> |
| * |
| * @return The number of keys, possibly zero, |
| * whose ready-operation sets were updated |
| * |
| * @throws IOException |
| * If an I/O error occurs |
| * |
| * @throws ClosedSelectorException |
| * If this selector is closed |
| */ |
| public abstract int select() throws IOException; |
| |
| /** |
| * Selects and performs an action on the keys whose corresponding channels |
| * are ready for I/O operations. |
| * |
| * <p> This method performs a blocking <a href="#selop">selection |
| * operation</a>. It wakes up from querying the operating system only when |
| * at least one channel is selected, this selector's {@link #wakeup wakeup} |
| * method is invoked, the current thread is interrupted, or the given |
| * timeout period expires, whichever comes first. |
| * |
| * <p> The specified <i>action</i>'s {@link Consumer#accept(Object) accept} |
| * method is invoked with the key for each channel that is ready to perform |
| * an operation identified by its key's interest set. The {@code accept} |
| * method may be invoked more than once for the same key but with the |
| * ready-operation set containing a subset of the operations for which the |
| * channel is ready (as described above). The {@code accept} method is |
| * invoked while synchronized on the selector and its selected-key set. |
| * Great care must be taken to avoid deadlocking with other threads that |
| * also synchronize on these objects. Selection operations are not reentrant |
| * in general and consequently the <i>action</i> should take great care not |
| * to attempt a selection operation on the same selector. The behavior when |
| * attempting a reentrant selection operation is implementation specific and |
| * therefore not specified. If the <i>action</i> closes the selector then |
| * {@code ClosedSelectorException} is thrown when the action completes. |
| * The <i>action</i> is not prohibited from closing channels registered with |
| * the selector, nor prohibited from cancelling keys or changing a key's |
| * interest set. If a channel is selected but its key is cancelled or its |
| * interest set changed before the <i>action</i> is performed on the key |
| * then it is implementation specific as to whether the <i>action</i> is |
| * invoked (it may be invoked with an {@link SelectionKey#isValid() invalid} |
| * key). Exceptions thrown by the action are relayed to the caller. |
| * |
| * <p> This method does not offer real-time guarantees: It schedules the |
| * timeout as if by invoking the {@link Object#wait(long)} method. |
| * |
| * @implSpec The default implementation removes all keys from the |
| * selected-key set, invokes {@link #select(long) select(long)} with the |
| * given timeout and then performs the action for each key added to the |
| * selected-key set. The default implementation does not detect the action |
| * performing a reentrant selection operation. The selected-key set may |
| * or may not be empty on completion of the default implementation. |
| * |
| * @param action The action to perform |
| * |
| * @param timeout If positive, block for up to {@code timeout} |
| * milliseconds, more or less, while waiting for a |
| * channel to become ready; if zero, block indefinitely; |
| * must not be negative |
| * |
| * @return The number of unique keys consumed, possibly zero |
| * |
| * @throws IOException |
| * If an I/O error occurs |
| * |
| * @throws ClosedSelectorException |
| * If this selector is closed or is closed by the action |
| * |
| * @throws IllegalArgumentException |
| * If the value of the timeout argument is negative |
| * |
| * @since 11 |
| */ |
| public int select(Consumer<SelectionKey> action, long timeout) |
| throws IOException |
| { |
| if (timeout < 0) |
| throw new IllegalArgumentException("Negative timeout"); |
| return doSelect(Objects.requireNonNull(action), timeout); |
| } |
| |
| /** |
| * Selects and performs an action on the keys whose corresponding channels |
| * are ready for I/O operations. |
| * |
| * <p> This method performs a blocking <a href="#selop">selection |
| * operation</a>. It wakes up from querying the operating system only when |
| * at least one channel is selected, this selector's {@link #wakeup wakeup} |
| * method is invoked, or the current thread is interrupted, whichever comes |
| * first. |
| * |
| * <p> This method is equivalent to invoking the 2-arg |
| * {@link #select(Consumer, long) select} method with a timeout of {@code 0} |
| * to block indefinitely. </p> |
| * |
| * @implSpec The default implementation invokes the 2-arg {@code select} |
| * method with a timeout of {@code 0}. |
| * |
| * @param action The action to perform |
| * |
| * @return The number of unique keys consumed, possibly zero |
| * |
| * @throws IOException |
| * If an I/O error occurs |
| * |
| * @throws ClosedSelectorException |
| * If this selector is closed or is closed by the action |
| * |
| * @since 11 |
| */ |
| public int select(Consumer<SelectionKey> action) throws IOException { |
| return select(action, 0); |
| } |
| |
| /** |
| * Selects and performs an action on the keys whose corresponding channels |
| * are ready for I/O operations. |
| * |
| * <p> This method performs a non-blocking <a href="#selop">selection |
| * operation</a>. |
| * |
| * <p> Invoking this method clears the effect of any previous invocations |
| * of the {@link #wakeup wakeup} method. </p> |
| * |
| * @implSpec The default implementation removes all keys from the |
| * selected-key set, invokes {@link #selectNow() selectNow()} and then |
| * performs the action for each key added to the selected-key set. The |
| * default implementation does not detect the action performing a reentrant |
| * selection operation. The selected-key set may or may not be empty on |
| * completion of the default implementation. |
| * |
| * @param action The action to perform |
| * |
| * @return The number of unique keys consumed, possibly zero |
| * |
| * @throws IOException |
| * If an I/O error occurs |
| * |
| * @throws ClosedSelectorException |
| * If this selector is closed or is closed by the action |
| * |
| * @since 11 |
| */ |
| public int selectNow(Consumer<SelectionKey> action) throws IOException { |
| return doSelect(Objects.requireNonNull(action), -1); |
| } |
| |
| /** |
| * Default implementation of select(Consumer) and selectNow(Consumer). |
| */ |
| private int doSelect(Consumer<SelectionKey> action, long timeout) |
| throws IOException |
| { |
| synchronized (this) { |
| Set<SelectionKey> selectedKeys = selectedKeys(); |
| synchronized (selectedKeys) { |
| selectedKeys.clear(); |
| int numKeySelected; |
| if (timeout < 0) { |
| numKeySelected = selectNow(); |
| } else { |
| numKeySelected = select(timeout); |
| } |
| |
| // copy selected-key set as action may remove keys |
| Set<SelectionKey> keysToConsume = Set.copyOf(selectedKeys); |
| assert keysToConsume.size() == numKeySelected; |
| selectedKeys.clear(); |
| |
| // invoke action for each selected key |
| keysToConsume.forEach(k -> { |
| action.accept(k); |
| if (!isOpen()) |
| throw new ClosedSelectorException(); |
| }); |
| |
| return numKeySelected; |
| } |
| } |
| } |
| |
| |
| /** |
| * Causes the first selection operation that has not yet returned to return |
| * immediately. |
| * |
| * <p> If another thread is currently blocked in a selection operation then |
| * that invocation will return immediately. If no selection operation is |
| * currently in progress then the next invocation of a selection operation |
| * will return immediately unless {@link #selectNow()} or {@link |
| * #selectNow(Consumer)} is invoked in the meantime. In any case the value |
| * returned by that invocation may be non-zero. Subsequent selection |
| * operations will block as usual unless this method is invoked again in the |
| * meantime. |
| * |
| * <p> Invoking this method more than once between two successive selection |
| * operations has the same effect as invoking it just once. </p> |
| * |
| * @return This selector |
| */ |
| public abstract Selector wakeup(); |
| |
| /** |
| * Closes this selector. |
| * |
| * <p> If a thread is currently blocked in one of this selector's selection |
| * methods then it is interrupted as if by invoking the selector's {@link |
| * #wakeup wakeup} method. |
| * |
| * <p> Any uncancelled keys still associated with this selector are |
| * invalidated, their channels are deregistered, and any other resources |
| * associated with this selector are released. |
| * |
| * <p> If this selector is already closed then invoking this method has no |
| * effect. |
| * |
| * <p> After a selector is closed, any further attempt to use it, except by |
| * invoking this method or the {@link #wakeup wakeup} method, will cause a |
| * {@link ClosedSelectorException} to be thrown. </p> |
| * |
| * @throws IOException |
| * If an I/O error occurs |
| */ |
| public abstract void close() throws IOException; |
| } |
