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* <td ALIGN=CENTER>Throws exception * <td ALIGN=CENTER>Special value * <td ALIGN=CENTER>Blocks * <td ALIGN=CENTER>Times out * </tr> * <tr> * <td>Insert * <td>{@link #add add(e)} * <td>{@link #offer offer(e)} * <td>{@link #put put(e)} * <td>{@link #offer(Object, long, TimeUnit) offer(e, time, unit)} * </tr> * <tr> * <td>Remove * <td>{@link #remove remove()} * <td>{@link #poll poll()} * <td>{@link #take take()} * <td>{@link #poll(long, TimeUnit) poll(time, unit)} * </tr> * <tr> * <td>Examine * <td>{@link #element element()} * <td>{@link #peek peek()} * <td>not applicable * <td>not applicable * </tr> * </table> * * <p>A BlockingQueue does not accept null elements. * Implementations throw <tt>NullPointerException on attempts * to <tt>add, put or offer a null. A * <tt>null is used as a sentinel value to indicate failure of * <tt>poll operations. * * <p>A BlockingQueue may be capacity bounded. At any given * time it may have a <tt>remainingCapacity beyond which no * additional elements can be <tt>put without blocking. * A <tt>BlockingQueue without any intrinsic capacity constraints always * reports a remaining capacity of <tt>Integer.MAX_VALUE. * * <p> BlockingQueue implementations are designed to be used * primarily for producer-consumer queues, but additionally support * the {@link java.util.Collection} interface. So, for example, it is * possible to remove an arbitrary element from a queue using * <tt>remove(x). However, such operations are in general * <em>not performed very efficiently, and are intended for only * occasional use, such as when a queued message is cancelled. * * <p> BlockingQueue implementations are thread-safe. All * queuing methods achieve their effects atomically using internal * locks or other forms of concurrency control. However, the * <em>bulk Collection operations addAll, * <tt>containsAll, retainAll and removeAll are * <em>not necessarily performed atomically unless specified * otherwise in an implementation. So it is possible, for example, for * <tt>addAll(c) to fail (throwing an exception) after adding * only some of the elements in <tt>c. * * <p>A BlockingQueue does not intrinsically support * any kind of "close" or "shutdown" operation to * indicate that no more items will be added. The needs and usage of * such features tend to be implementation-dependent. For example, a * common tactic is for producers to insert special * <em>end-of-stream or poison objects, that are * interpreted accordingly when taken by consumers. * * <p> * Usage example, based on a typical producer-consumer scenario. * Note that a <tt>BlockingQueue can safely be used with multiple * producers and multiple consumers. * <pre> * class Producer implements Runnable { * private final BlockingQueue queue; * Producer(BlockingQueue q) { queue = q; } * public void run() { * try { * while (true) { queue.put(produce()); } * } catch (InterruptedException ex) { ... handle ...} * } * Object produce() { ... } * } * * class Consumer implements Runnable { * private final BlockingQueue queue; * Consumer(BlockingQueue q) { queue = q; } * public void run() { * try { * while (true) { consume(queue.take()); } * } catch (InterruptedException ex) { ... handle ...} * } * void consume(Object x) { ... } * } * * class Setup { * void main() { * BlockingQueue q = new SomeQueueImplementation(); * Producer p = new Producer(q); * Consumer c1 = new Consumer(q); * Consumer c2 = new Consumer(q); * new Thread(p).start(); * new Thread(c1).start(); * new Thread(c2).start(); * } * } * </pre> * * <p>Memory consistency effects: As with other concurrent * collections, actions in a thread prior to placing an object into a * {@code BlockingQueue} * <a href="package-summary.html#MemoryVisibility">happen-before * actions subsequent to the access or removal of that element from * the {@code BlockingQueue} in another thread. * * <p>This interface is a member of the * <a href="{@docRoot}/../technotes/guides/collections/index.html"> * Java Collections Framework</a>. * * @since 1.5 * @author Doug Lea * @param <E> the type of elements held in this collection */ public interface BlockingQueue<E> extends java.util.Queue { /** * Inserts the specified element into this queue if it is possible to do * so immediately without violating capacity restrictions, returning * <tt>true upon success and throwing an * <tt>IllegalStateException if no space is currently available. * When using a capacity-restricted queue, it is generally preferable to * use {@link #offer(Object) offer}. * * @param e the element to add * @return <tt>true (as specified by {@link Collection#add}) * @throws IllegalStateException if the element cannot be added at this * time due to capacity restrictions * @throws ClassCastException if the class of the specified element * prevents it from being added to this queue * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException if some property of the specified * element prevents it from being added to this queue */ boolean add(E e); /** * Inserts the specified element into this queue if it is possible to do * so immediately without violating capacity restrictions, returning * <tt>true upon success and false if no space is currently * available. When using a capacity-restricted queue, this method is * generally preferable to {@link #add}, which can fail to insert an * element only by throwing an exception. * * @param e the element to add * @return <tt>true if the element was added to this queue, else * <tt>false * @throws ClassCastException if the class of the specified element * prevents it from being added to this queue * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException if some property of the specified * element prevents it from being added to this queue */ boolean offer(E e); /** * Inserts the specified element into this queue, 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 queue * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException if some property of the specified * element prevents it from being added to this queue */ void put(E e) throws InterruptedException; /** * Inserts the specified element into this queue, 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 * <tt>unit * @param unit a <tt>TimeUnit determining how to interpret the * <tt>timeout parameter * @return <tt>true if successful, or 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 queue * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException if some property of the specified * element prevents it from being added to this queue */ boolean offer(E e, long timeout, TimeUnit unit) throws InterruptedException; /** * Retrieves and removes the head of this queue, waiting if necessary * until an element becomes available. * * @return the head of this queue * @throws InterruptedException if interrupted while waiting */ E take() throws InterruptedException; /** * Retrieves and removes the head of this queue, 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 * <tt>unit * @param unit a <tt>TimeUnit determining how to interpret the * <tt>timeout parameter * @return the head of this queue, or <tt>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; /** * Returns the number of additional elements that this queue can ideally * (in the absence of memory or resource constraints) accept without * blocking, or <tt>Integer.MAX_VALUE if there is no intrinsic * limit. * * <p>Note that you cannot always tell if an attempt to insert * an element will succeed by inspecting <tt>remainingCapacity * because it may be the case that another thread is about to * insert or remove an element. * * @return the remaining capacity */ int remainingCapacity(); /** * Removes a single instance of the specified element from this queue, * if it is present. More formally, removes an element <tt>e such * that <tt>o.equals(e), if this queue contains one or more such * elements. * Returns <tt>true if this queue contained the specified element * (or equivalently, if this queue changed as a result of the call). * * @param o element to be removed from this queue, if present * @return <tt>true if this queue changed as a result of the call * @throws ClassCastException if the class of the specified element * is incompatible with this queue (optional) * @throws NullPointerException if the specified element is null (optional) */ boolean remove(Object o); /** * Returns <tt>true if this queue contains the specified element. * More formally, returns <tt>true if and only if this queue contains * at least one element <tt>e such that o.equals(e). * * @param o object to be checked for containment in this queue * @return <tt>true if this queue contains the specified element * @throws ClassCastException if the class of the specified element * is incompatible with this queue (optional) * @throws NullPointerException if the specified element is null (optional) */ public boolean contains(Object o); /** * Removes all available elements from this queue and adds them * to the given collection. This operation may be more * efficient than repeatedly polling this queue. A failure * encountered while attempting to add elements to * collection <tt>c may result in elements being in neither, * either or both collections when the associated exception is * thrown. Attempts to drain a queue to itself result in * <tt>IllegalArgumentException. Further, the behavior of * this operation is undefined if the specified collection is * modified while the operation is in progress. * * @param c the collection to transfer elements into * @return the number of elements transferred * @throws UnsupportedOperationException if addition of elements * is not supported by the specified collection * @throws ClassCastException if the class of an element of this queue * prevents it from being added to the specified collection * @throws NullPointerException if the specified collection is null * @throws IllegalArgumentException if the specified collection is this * queue, or some property of an element of this queue prevents * it from being added to the specified collection */ int drainTo(Collection<? super E> c); /** * Removes at most the given number of available elements from * this queue and adds them to the given collection. A failure * encountered while attempting to add elements to * collection <tt>c may result in elements being in neither, * either or both collections when the associated exception is * thrown. Attempts to drain a queue to itself result in * <tt>IllegalArgumentException. Further, the behavior of * this operation is undefined if the specified collection is * modified while the operation is in progress. * * @param c the collection to transfer elements into * @param maxElements the maximum number of elements to transfer * @return the number of elements transferred * @throws UnsupportedOperationException if addition of elements * is not supported by the specified collection * @throws ClassCastException if the class of an element of this queue * prevents it from being added to the specified collection * @throws NullPointerException if the specified collection is null * @throws IllegalArgumentException if the specified collection is this * queue, or some property of an element of this queue prevents * it from being added to the specified collection */ int drainTo(Collection<? super E> c, int maxElements); }

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Scala example source code file (BlockingQueue.java)

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Java - Scala tags/keywords

blockingqueue, blockingqueue, e, e, interruptedexception, interruptedexception, timeunit, timeunit, util

The Scala BlockingQueue.java source code

/*
 * 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/licenses/publicdomain
 */

package scala.actors.threadpool;

import java.util.Collection;
import java.util.Queue;

/**
 * A {@link java.util.Queue} that additionally supports operations
 * that wait for the queue to become non-empty when retrieving an
 * element, and wait for space to become available in the queue when
 * storing an element.
 *
 * <p>BlockingQueue 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
 * <tt>null or 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:
 *
 * <p>
 * <table BORDER CELLPADDING=3 CELLSPACING=1>
 *  <tr>
 *    <td>
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