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/* * 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. */ /* * This file is available under and governed by the GNU General Public * License version 2 only, as published by the Free Software Foundation. * However, the following notice accompanied the original version of this * file: * * Written by Doug Lea with assistance from members of JCP JSR-166 * Expert Group and released to the public domain, as explained at * http://creativecommons.org/publicdomain/zero/1.0/ */ package java.util.concurrent; import java.util.Deque; import java.util.Iterator; import java.util.NoSuchElementException; /** * A {@link Deque} that additionally supports blocking operations that wait * for the deque to become non-empty when retrieving an element, and wait for * space to become available in the deque when storing an element. * * <p>{@code BlockingDeque} methods come in four forms, with different ways * of handling operations that cannot be satisfied immediately, but may be * satisfied at some point in the future: * one throws an exception, the second returns a special value (either * {@code null} or {@code false}, depending on the operation), the third * blocks the current thread indefinitely until the operation can succeed, * and the fourth blocks for only a given maximum time limit before giving * up. These methods are summarized in the following table: * * <table class="plain"> * <caption>Summary of BlockingDeque methods</caption> * <tr> * <th id="First" colspan="5"> First Element (Head)</th> * </tr> * <tr> * <td></td> * <th id="FThrow" style="font-weight:normal; font-style: italic">Throws exception</th> * <th id="FValue" style="font-weight:normal; font-style: italic">Special value</th> * <th id="FBlock" style="font-weight:normal; font-style: italic">Blocks</th> * <th id="FTimes" style="font-weight:normal; font-style: italic">Times out</th> * </tr> * <tr> * <th id="FInsert" style="text-align:left">Insert</th> * <td headers="First FInsert FThrow">{@link #addFirst(Object) addFirst(e)}</td> * <td headers="First FInsert FValue">{@link #offerFirst(Object) offerFirst(e)}</td> * <td headers="First FInsert FBlock">{@link #putFirst(Object) putFirst(e)}</td> * <td headers="First FInsert FTimes">{@link #offerFirst(Object, long, TimeUnit) offerFirst(e, time, unit)}</td> * </tr> * <tr> * <th id="FRemove" style="text-align:left">Remove</th> * <td headers="First FRemove FThrow">{@link #removeFirst() removeFirst()}</td> * <td headers="First FRemove FValue">{@link #pollFirst() pollFirst()}</td> * <td headers="First FRemove FBlock">{@link #takeFirst() takeFirst()}</td> * <td headers="First FRemove FTimes">{@link #pollFirst(long, TimeUnit) pollFirst(time, unit)}</td> * </tr> * <tr> * <th id="FExamine" style="text-align:left">Examine</th> * <td headers="First FExamine FThrow">{@link #getFirst() getFirst()}</td> * <td headers="First FExamine FValue">{@link #peekFirst() peekFirst()}</td> * <td headers="First FExamine FBlock" style="font-style:italic">not applicable</td> * <td headers="First FExamine FTimes" style="font-style:italic">not applicable</td> * </tr> * <tr> * <th id="Last" colspan="5"> Last Element (Tail)</th> * </tr> * <tr> * <td></td> * <th id="LThrow" style="font-weight:normal; font-style: italic">Throws exception</th> * <th id="LValue" style="font-weight:normal; font-style: italic">Special value</th> * <th id="LBlock" style="font-weight:normal; font-style: italic">Blocks</th> * <th id="LTimes" style="font-weight:normal; font-style: italic">Times out</th> * </tr> * <tr> * <th id="LInsert" style="text-align:left">Insert</th> * <td headers="Last LInsert LThrow">{@link #addLast(Object) addLast(e)}</td> * <td headers="Last LInsert LValue">{@link #offerLast(Object) offerLast(e)}</td> * <td headers="Last LInsert LBlock">{@link #putLast(Object) putLast(e)}</td> * <td headers="Last LInsert LTimes">{@link #offerLast(Object, long, TimeUnit) offerLast(e, time, unit)}</td> * </tr> * <tr> * <th id="LRemove" style="text-align:left">Remove</th> * <td headers="Last LRemove LThrow">{@link #removeLast() removeLast()}</td> * <td headers="Last LRemove LValue">{@link #pollLast() pollLast()}</td> * <td headers="Last LRemove LBlock">{@link #takeLast() takeLast()}</td> * <td headers="Last LRemove LTimes">{@link #pollLast(long, TimeUnit) pollLast(time, unit)}</td> * </tr> * <tr> * <th id="LExamine" style="text-align:left">Examine</th> * <td headers="Last LExamine LThrow">{@link #getLast() getLast()}</td> * <td headers="Last LExamine LValue">{@link #peekLast() peekLast()}</td> * <td headers="Last LExamine LBlock" style="font-style:italic">not applicable</td> * <td headers="Last LExamine LTimes" style="font-style:italic">not applicable</td> * </tr> * </table> * * <p>Like any {@link BlockingQueue}, a {@code BlockingDeque} is thread safe, * does not permit null elements, and may (or may not) be * capacity-constrained. * * <p>A {@code BlockingDeque} implementation may be used directly as a FIFO * {@code BlockingQueue}. The methods inherited from the * {@code BlockingQueue} interface are precisely equivalent to * {@code BlockingDeque} methods as indicated in the following table: * * <table class="plain"> * <caption>Comparison of BlockingQueue and BlockingDeque methods</caption> * <tr> * <td></td> * <th id="BQueue"> {@code BlockingQueue} Method</th> * <th id="BDeque"> Equivalent {@code BlockingDeque} Method</th> * </tr> * <tr> * <th id="Insert" rowspan="4" style="text-align:left; vertical-align:top">Insert</th> * <th id="add" style="font-weight:normal; text-align:left">{@link #add(Object) add(e)}</th> * <td headers="Insert BDeque add">{@link #addLast(Object) addLast(e)}</td> * </tr> * <tr> * <th id="offer1" style="font-weight:normal; text-align:left">{@link #offer(Object) offer(e)}</th> * <td headers="Insert BDeque offer1">{@link #offerLast(Object) offerLast(e)}</td> * </tr> * <tr> * <th id="put" style="font-weight:normal; text-align:left">{@link #put(Object) put(e)}</th> * <td headers="Insert BDeque put">{@link #putLast(Object) putLast(e)}</td> * </tr> * <tr> * <th id="offer2" style="font-weight:normal; text-align:left">{@link #offer(Object, long, TimeUnit) offer(e, time, unit)}</th> * <td headers="Insert BDeque offer2">{@link #offerLast(Object, long, TimeUnit) offerLast(e, time, unit)}</td> * </tr> * <tr> * <th id="Remove" rowspan="4" style="text-align:left; vertical-align:top">Remove</th> * <th id="remove" style="font-weight:normal; text-align:left">{@link #remove() remove()}</th> * <td headers="Remove BDeque remove">{@link #removeFirst() removeFirst()}</td> * </tr> * <tr> * <th id="poll1" style="font-weight:normal; text-align:left">{@link #poll() poll()}</th> * <td headers="Remove BDeque poll1">{@link #pollFirst() pollFirst()}</td> * </tr> * <tr> * <th id="take" style="font-weight:normal; text-align:left">{@link #take() take()}</th> * <td headers="Remove BDeque take">{@link #takeFirst() takeFirst()}</td> * </tr> * <tr> * <th id="poll2" style="font-weight:normal; text-align:left">{@link #poll(long, TimeUnit) poll(time, unit)}</th> * <td headers="Remove BDeque poll2">{@link #pollFirst(long, TimeUnit) pollFirst(time, unit)}</td> * </tr> * <tr> * <th id="Examine" rowspan="2" style="text-align:left; vertical-align:top">Examine</th> * <th id="element" style="font-weight:normal; text-align:left">{@link #element() element()}</th> * <td headers="Examine BDeque element">{@link #getFirst() getFirst()}</td> * </tr> * <tr> * <th id="peek" style="font-weight:normal; text-align:left">{@link #peek() peek()}</th> * <td headers="Examine BDeque peek">{@link #peekFirst() peekFirst()}</td> * </tr> * </table> * * <p>Memory consistency effects: As with other concurrent * collections, actions in a thread prior to placing an object into a * {@code BlockingDeque} * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a> * actions subsequent to the access or removal of that element from * the {@code BlockingDeque} in another thread. * * <p>This interface is a member of the * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework"> * Java Collections Framework</a>. * * @since 1.6 * @author Doug Lea * @param <E> the type of elements held in this deque */ public interface BlockingDeque<E> extends BlockingQueue<E>, Deque<E> { /* * We have "diamond" multiple interface inheritance here, and that * introduces ambiguities. Methods might end up with different * specs depending on the branch chosen by javadoc. Thus a lot of * methods specs here are copied from superinterfaces. */ /** * Inserts the specified element at the front of this deque if it is * possible to do so immediately without violating capacity restrictions, * throwing an {@code IllegalStateException} if no space is currently * available. When using a capacity-restricted deque, it is generally * preferable to use {@link #offerFirst(Object) offerFirst}. * * @param e the element to add * @throws IllegalStateException {@inheritDoc} * @throws ClassCastException {@inheritDoc} * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException {@inheritDoc} */ void addFirst(E e); /** * Inserts the specified element at the end of this deque if it is * possible to do so immediately without violating capacity restrictions, * throwing an {@code IllegalStateException} if no space is currently * available. When using a capacity-restricted deque, it is generally * preferable to use {@link #offerLast(Object) offerLast}. * * @param e the element to add * @throws IllegalStateException {@inheritDoc} * @throws ClassCastException {@inheritDoc} * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException {@inheritDoc} */ void addLast(E e); /** * Inserts the specified element at the front of this deque if it is * possible to do so immediately without violating capacity restrictions, * returning {@code true} upon success and {@code false} if no space is * currently available. * When using a capacity-restricted deque, this method is generally * preferable to the {@link #addFirst(Object) addFirst} method, which can * fail to insert an element only by throwing an exception. * * @param e the element to add * @throws ClassCastException {@inheritDoc} * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException {@inheritDoc} */ boolean offerFirst(E e); /** * Inserts the specified element at the end of this deque if it is * possible to do so immediately without violating capacity restrictions, * returning {@code true} upon success and {@code false} if no space is * currently available. * When using a capacity-restricted deque, this method is generally * preferable to the {@link #addLast(Object) addLast} method, which can * fail to insert an element only by throwing an exception. * * @param e the element to add * @throws ClassCastException {@inheritDoc} * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException {@inheritDoc} */ boolean offerLast(E e); /** * Inserts the specified element at the front of this deque, * waiting if necessary for space to become available. * * @param e the element to add * @throws InterruptedException if interrupted while waiting * @throws ClassCastException if the class of the specified element * prevents it from being added to this deque * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException if some property of the specified * element prevents it from being added to this deque */ void putFirst(E e) throws InterruptedException; /** * Inserts the specified element at the end of this deque, * waiting if necessary for space to become available. * * @param e the element to add * @throws InterruptedException if interrupted while waiting * @throws ClassCastException if the class of the specified element * prevents it from being added to this deque * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException if some property of the specified * element prevents it from being added to this deque */ void putLast(E e) throws InterruptedException; /** * Inserts the specified element at the front of this deque, * waiting up to the specified wait time if necessary for space to * become available. * * @param e the element to add * @param timeout how long to wait before giving up, in units of * {@code unit} * @param unit a {@code TimeUnit} determining how to interpret the * {@code timeout} parameter * @return {@code true} if successful, or {@code false} if * the specified waiting time elapses before space is available * @throws InterruptedException if interrupted while waiting * @throws ClassCastException if the class of the specified element * prevents it from being added to this deque * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException if some property of the specified * element prevents it from being added to this deque */ boolean offerFirst(E e, long timeout, TimeUnit unit) throws InterruptedException; /** * Inserts the specified element at the end of this deque, * waiting up to the specified wait time if necessary for space to * become available. * * @param e the element to add * @param timeout how long to wait before giving up, in units of * {@code unit} * @param unit a {@code TimeUnit} determining how to interpret the * {@code timeout} parameter * @return {@code true} if successful, or {@code false} if * the specified waiting time elapses before space is available * @throws InterruptedException if interrupted while waiting * @throws ClassCastException if the class of the specified element * prevents it from being added to this deque * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException if some property of the specified * element prevents it from being added to this deque */ boolean offerLast(E e, long timeout, TimeUnit unit) throws InterruptedException; /** * Retrieves and removes the first element of this deque, waiting * if necessary until an element becomes available. * * @return the head of this deque * @throws InterruptedException if interrupted while waiting */ E takeFirst() throws InterruptedException; /** * Retrieves and removes the last element of this deque, waiting * if necessary until an element becomes available. * * @return the tail of this deque * @throws InterruptedException if interrupted while waiting */ E takeLast() throws InterruptedException; /** * Retrieves and removes the first element of this deque, waiting * up to the specified wait time if necessary for an element to * become available. * * @param timeout how long to wait before giving up, in units of * {@code unit} * @param unit a {@code TimeUnit} determining how to interpret the * {@code timeout} parameter * @return the head of this deque, or {@code null} if the specified * waiting time elapses before an element is available * @throws InterruptedException if interrupted while waiting */ E pollFirst(long timeout, TimeUnit unit) throws InterruptedException; /** * Retrieves and removes the last element of this deque, waiting * up to the specified wait time if necessary for an element to * become available. * * @param timeout how long to wait before giving up, in units of * {@code unit} * @param unit a {@code TimeUnit} determining how to interpret the * {@code timeout} parameter * @return the tail of this deque, or {@code null} if the specified * waiting time elapses before an element is available * @throws InterruptedException if interrupted while waiting */ E pollLast(long timeout, TimeUnit unit) throws InterruptedException; /** * Removes the first occurrence of the specified element from this deque. * If the deque does not contain the element, it is unchanged. * More formally, removes the first element {@code e} such that * {@code o.equals(e)} (if such an element exists). * Returns {@code true} if this deque contained the specified element * (or equivalently, if this deque changed as a result of the call). * * @param o element to be removed from this deque, if present * @return {@code true} if an element was removed as a result of this call * @throws ClassCastException if the class of the specified element * is incompatible with this deque * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>) * @throws NullPointerException if the specified element is null * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>) */ boolean removeFirstOccurrence(Object o); /** * Removes the last occurrence of the specified element from this deque. * If the deque does not contain the element, it is unchanged. * More formally, removes the last element {@code e} such that * {@code o.equals(e)} (if such an element exists). * Returns {@code true} if this deque contained the specified element * (or equivalently, if this deque changed as a result of the call). * * @param o element to be removed from this deque, if present * @return {@code true} if an element was removed as a result of this call * @throws ClassCastException if the class of the specified element * is incompatible with this deque * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>) * @throws NullPointerException if the specified element is null * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>) */ boolean removeLastOccurrence(Object o); // *** BlockingQueue methods *** /** * Inserts the specified element into the queue represented by this deque * (in other words, at the tail of this deque) if it is possible to do so * immediately without violating capacity restrictions, returning * {@code true} upon success and throwing an * {@code IllegalStateException} if no space is currently available. * When using a capacity-restricted deque, it is generally preferable to * use {@link #offer(Object) offer}. * * <p>This method is equivalent to {@link #addLast(Object) addLast}. * * @param e the element to add * @throws IllegalStateException {@inheritDoc} * @throws ClassCastException if the class of the specified element * prevents it from being added to this deque * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException if some property of the specified * element prevents it from being added to this deque */ boolean add(E e); /** * Inserts the specified element into the queue represented by this deque * (in other words, at the tail of this deque) if it is possible to do so * immediately without violating capacity restrictions, returning * {@code true} upon success and {@code false} if no space is currently * available. When using a capacity-restricted deque, this method is * generally preferable to the {@link #add} method, which can fail to * insert an element only by throwing an exception. * * <p>This method is equivalent to {@link #offerLast(Object) offerLast}. * * @param e the element to add * @throws ClassCastException if the class of the specified element * prevents it from being added to this deque * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException if some property of the specified * element prevents it from being added to this deque */ boolean offer(E e); /** * Inserts the specified element into the queue represented by this deque * (in other words, at the tail of this deque), waiting if necessary for * space to become available. * * <p>This method is equivalent to {@link #putLast(Object) putLast}. * * @param e the element to add * @throws InterruptedException {@inheritDoc} * @throws ClassCastException if the class of the specified element * prevents it from being added to this deque * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException if some property of the specified * element prevents it from being added to this deque */ void put(E e) throws InterruptedException; /** * Inserts the specified element into the queue represented by this deque * (in other words, at the tail of this deque), waiting up to the * specified wait time if necessary for space to become available. * * <p>This method is equivalent to * {@link #offerLast(Object,long,TimeUnit) offerLast}. * * @param e the element to add * @return {@code true} if the element was added to this deque, else * {@code false} * @throws InterruptedException {@inheritDoc} * @throws ClassCastException if the class of the specified element * prevents it from being added to this deque * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException if some property of the specified * element prevents it from being added to this deque */ boolean offer(E e, long timeout, TimeUnit unit) throws InterruptedException; /** * Retrieves and removes the head of the queue represented by this deque * (in other words, the first element of this deque). * This method differs from {@link #poll() poll()} only in that it * throws an exception if this deque is empty. * * <p>This method is equivalent to {@link #removeFirst() removeFirst}. * * @return the head of the queue represented by this deque * @throws NoSuchElementException if this deque is empty */ E remove(); /** * Retrieves and removes the head of the queue represented by this deque * (in other words, the first element of this deque), or returns * {@code null} if this deque is empty. * * <p>This method is equivalent to {@link #pollFirst()}. * * @return the head of this deque, or {@code null} if this deque is empty */ E poll(); /** * Retrieves and removes the head of the queue represented by this deque * (in other words, the first element of this deque), waiting if * necessary until an element becomes available. * * <p>This method is equivalent to {@link #takeFirst() takeFirst}. * * @return the head of this deque * @throws InterruptedException if interrupted while waiting */ E take() throws InterruptedException; /** * Retrieves and removes the head of the queue represented by this deque * (in other words, the first element of this deque), waiting up to the * specified wait time if necessary for an element to become available. * * <p>This method is equivalent to * {@link #pollFirst(long,TimeUnit) pollFirst}. * * @return the head of this deque, or {@code null} if the * specified waiting time elapses before an element is available * @throws InterruptedException if interrupted while waiting */ E poll(long timeout, TimeUnit unit) throws InterruptedException; /** * Retrieves, but does not remove, the head of the queue represented by * this deque (in other words, the first element of this deque). * This method differs from {@link #peek() peek} only in that it throws an * exception if this deque is empty. * * <p>This method is equivalent to {@link #getFirst() getFirst}. * * @return the head of this deque * @throws NoSuchElementException if this deque is empty */ E element(); /** * Retrieves, but does not remove, the head of the queue represented by * this deque (in other words, the first element of this deque), or * returns {@code null} if this deque is empty. * * <p>This method is equivalent to {@link #peekFirst() peekFirst}. * * @return the head of this deque, or {@code null} if this deque is empty */ E peek(); /** * Removes the first occurrence of the specified element from this deque. * If the deque does not contain the element, it is unchanged. * More formally, removes the first element {@code e} such that * {@code o.equals(e)} (if such an element exists). * Returns {@code true} if this deque contained the specified element * (or equivalently, if this deque changed as a result of the call). * * <p>This method is equivalent to * {@link #removeFirstOccurrence(Object) removeFirstOccurrence}. * * @param o element to be removed from this deque, if present * @return {@code true} if this deque changed as a result of the call * @throws ClassCastException if the class of the specified element * is incompatible with this deque * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>) * @throws NullPointerException if the specified element is null * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>) */ boolean remove(Object o); /** * Returns {@code true} if this deque contains the specified element. * More formally, returns {@code true} if and only if this deque contains * at least one element {@code e} such that {@code o.equals(e)}. * * @param o object to be checked for containment in this deque * @return {@code true} if this deque contains the specified element * @throws ClassCastException if the class of the specified element * is incompatible with this deque * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>) * @throws NullPointerException if the specified element is null * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>) */ boolean contains(Object o); /** * Returns the number of elements in this deque. * * @return the number of elements in this deque */ int size(); /** * Returns an iterator over the elements in this deque in proper sequence. * The elements will be returned in order from first (head) to last (tail). * * @return an iterator over the elements in this deque in proper sequence */ Iterator<E> iterator(); // *** Stack methods *** /** * Pushes an element onto the stack represented by this deque (in other * words, at the head of this deque) if it is possible to do so * immediately without violating capacity restrictions, throwing an * {@code IllegalStateException} if no space is currently available. * * <p>This method is equivalent to {@link #addFirst(Object) addFirst}. * * @throws IllegalStateException {@inheritDoc} * @throws ClassCastException {@inheritDoc} * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException {@inheritDoc} */ void push(E e); }