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/* Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
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package java.nio.channels;

import java.io.Closeable;
import java.io.IOException;
import java.nio.channels.spi.SelectorProvider;
import java.util.Set;

/**
 * A controller for the selection of {@link SelectableChannel} objects.
 * Selectable channels can be registered with a selector and get a
 * {@link SelectionKey} that represents the registration. The keys are also
 * added to the selector's key set. Selection keys can be canceled so that the
 * corresponding channel is no longer registered with the selector.
 * 

* By invoking the {@code select} method, the key set is checked and all keys * that have been canceled since last select operation are moved to the set of * canceled keys. During the select operation, the channels registered with this * selector are checked to see whether they are ready for operation according to * their {@link SelectionKey interest set}. */ public abstract class Selector implements Closeable { /** * Returns a selector returned by {@link SelectorProvider#provider}'s * {@link SelectorProvider#openSelector} method. * * @throws IOException * if an I/O error occurs. */ public static Selector open() throws IOException { return SelectorProvider.provider().openSelector(); } /** * Constructs a new {@code Selector}. */ protected Selector() { } /** * Closes this selector. Ongoing calls to the {@code select} methods of this * selector will get interrupted. This interruption behaves as if the * {@link #wakeup()} method of this selector is called. After this, all keys * that are still valid are invalidated and their channels are unregistered. * All resources held by this selector are released. *

* Any further attempt of using this selector after this method has been * called (except calling {@link #close()} or {@link #wakeup()}) results in * a {@link ClosedSelectorException} being thrown. * * @throws IOException * if an I/O error occurs. */ public abstract void close() throws IOException; /** * Indicates whether this selector is open. * * @return {@code true} if this selector is not closed, {@code false} * otherwise. */ public abstract boolean isOpen(); /** * Gets the set of registered keys. The set is immutable and is not thread- * safe. * * @return the set of registered keys. */ public abstract Set keys(); /** * Gets the provider of this selector. * * @return the provider of this selector. */ public abstract SelectorProvider provider(); /** * Detects if any of the registered channels is ready for I/O operations * according to its {@link SelectionKey interest set}. This method does not * return until at least one channel is ready, {@link #wakeup()} is * invoked or the calling thread is interrupted. * * @return the number of channels that are ready for operation. * @throws IOException * if an I/O error occurs. * @throws ClosedSelectorException * if the selector is closed. */ public abstract int select() throws IOException; /** * Detects if any of the registered channels is ready for I/O operations * according to its {@link SelectionKey interest set}. This method does not * return until at least one channel is ready, {@link #wakeup()} is invoked, * the calling thread is interrupted or the specified {@code timeout} * expires. * * @param timeout * the non-negative timeout in millisecond; 0 will block forever * if no channels get ready. * @return the number of channels that are ready for operation. * @throws ClosedSelectorException * if the selector is closed. * @throws IllegalArgumentException * if the given timeout argument is less than zero. * @throws IOException * if an I/O error occurs. */ public abstract int select(long timeout) throws IOException; /** * Gets the selection keys whose channels are ready for operation. The set * is not thread-safe and no keys may be added to it. Removing keys is * allowed. * * @return the selection keys whose channels are ready for operation. * @throws ClosedSelectorException * if the selector is closed. */ public abstract Set selectedKeys(); /** * Detects if any of the registered channels is ready for I/O operations * according to its {@link SelectionKey interest set}. This operation will * return immediately. * * @return the number of channels that are ready for operation, 0 if none is * ready. * @throws IOException * if an I/O error occurrs. * @throws ClosedSelectorException * if the selector is closed. */ public abstract int selectNow() throws IOException; /** * Forces blocked {@code select} operations to return immediately. *

* If no {@code select} operation is blocked when {@code wakeup()} is called * then the next {@code select} operation will return immediately. This can * be undone by a call to {@code selectNow()}; after calling * {@code selectNow()}, a subsequent call of {@code select} can block * again. * * @return this selector. * @throws ClosedSelectorException * if the selector is closed. */ public abstract Selector wakeup(); }





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