/*
* @(#)BlockingQueue.java 1.13 06/04/21
*
* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.util.concurrent;
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><tt>BlockingQueue</tt> 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</tt> or <tt>false</tt>, 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></td>
* <td ALIGN=CENTER><em>Throws exception</em></td>
* <td ALIGN=CENTER><em>Special value</em></td>
* <td ALIGN=CENTER><em>Blocks</em></td>
* <td ALIGN=CENTER><em>Times out</em></td>
* </tr>
* <tr>
* <td><b>Insert</b></td>
* <td>{@link #add add(e)}</td>
* <td>{@link #offer offer(e)}</td>
* <td>{@link #put put(e)}</td>
* <td>{@link #offer(Object, long, TimeUnit) offer(e, time, unit)}</td>
* </tr>
* <tr>
* <td><b>Remove</b></td>
* <td>{@link #remove remove()}</td>
* <td>{@link #poll poll()}</td>
* <td>{@link #take take()}</td>
* <td>{@link #poll(long, TimeUnit) poll(time, unit)}</td>
* </tr>
* <tr>
* <td><b>Examine</b></td>
* <td>{@link #element element()}</td>
* <td>{@link #peek peek()}</td>
* <td><em>not applicable</em></td>
* <td><em>not applicable</em></td>
* </tr>
* </table>
*
* <p>A <tt>BlockingQueue</tt> does not accept <tt>null</tt> elements.
* Implementations throw <tt>NullPointerException</tt> on attempts
* to <tt>add</tt>, <tt>put</tt> or <tt>offer</tt> a <tt>null</tt>. A
* <tt>null</tt> is used as a sentinel value to indicate failure of
* <tt>poll</tt> operations.
*
* <p>A <tt>BlockingQueue</tt> may be capacity bounded. At any given
* time it may have a <tt>remainingCapacity</tt> beyond which no
* additional elements can be <tt>put</tt> without blocking.
* A <tt>BlockingQueue</tt> without any intrinsic capacity constraints always
* reports a remaining capacity of <tt>Integer.MAX_VALUE</tt>.
*
* <p> <tt>BlockingQueue</tt> 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)</tt>. However, such operations are in general
* <em>not</em> performed very efficiently, and are intended for only
* occasional use, such as when a queued message is cancelled.
*
* <p> <tt>BlockingQueue</tt> implementations are thread-safe. All
* queuing methods achieve their effects atomically using internal
* locks or other forms of concurrency control. However, the
* <em>bulk</em> Collection operations <tt>addAll</tt>,
* <tt>containsAll</tt>, <tt>retainAll</tt> and <tt>removeAll</tt> are
* <em>not</em> necessarily performed atomically unless specified
* otherwise in an implementation. So it is possible, for example, for
* <tt>addAll(c)</tt> to fail (throwing an exception) after adding
* only some of the elements in <tt>c</tt>.
*
* <p>A <tt>BlockingQueue</tt> does <em>not</em> 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</em> or <em>poison</em> objects, that are
* interpreted accordingly when taken by consumers.
*
* <p>
* Usage example, based on a typical producer-consumer scenario.
* Note that a <tt>BlockingQueue</tt> 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"><i>happen-before</i></a>
* 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 Queue<E> {
/**
* Inserts the specified element into this queue if it is possible to do
* so immediately without violating capacity restrictions, returning
* <tt>true</tt> upon success and throwing an
* <tt>IllegalStateException</tt> 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</tt> (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</tt> upon success and <tt>false</tt> 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</tt> if the element was added to this queue, else
* <tt>false</tt>
* @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</tt>
* @param unit a <tt>TimeUnit</tt> determining how to interpret the
* <tt>timeout</tt> parameter
* @return <tt>true</tt> if successful, or <tt>false</tt> 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</tt>
* @param unit a <tt>TimeUnit</tt> determining how to interpret the
* <tt>timeout</tt> parameter
* @return the head of this queue, or <tt>null</tt> 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</tt> if there is no intrinsic
* limit.
*
* <p>Note that you <em>cannot</em> always tell if an attempt to insert
* an element will succeed by inspecting <tt>remainingCapacity</tt>
* 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</tt> such
* that <tt>o.equals(e)</tt>, if this queue contains one or more such
* elements.
* Returns <tt>true</tt> 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</tt> 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</tt> if this queue contains the specified element.
* More formally, returns <tt>true</tt> if and only if this queue contains
* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
*
* @param o object to be checked for containment in this queue
* @return <tt>true</tt> 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</tt> 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</tt>. 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</tt> 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</tt>. 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);
}
|
