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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain. Use, modify, and |
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* redistribute this code in any way without acknowledgement. |
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*/ |
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package java.util.concurrent; |
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import java.util.Collection; |
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import java.util.Queue; |
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|
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/** |
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* A {@link java.util.Queue} that additionally supports operations |
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* that wait for elements to exist when retrieving them, and wait for |
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* space to exist when storing them. |
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* |
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* <p>A <tt>BlockingQueue</tt> does not accept <tt>null</tt> elements. |
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* Implementations throw <tt>NullPointerException</tt> on attempts |
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* to <tt>add</tt>, <tt>put</tt> or <tt>offer</tt> a <tt>null</tt>. A |
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* <tt>null</tt> is used as a sentinel value to indicate failure of |
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* <tt>poll</tt> operations. |
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* |
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* <p>A <tt>BlockingQueue</tt> may be capacity bounded. At any given |
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* time it may have a <tt>remainingCapacity</tt> beyond which no |
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* additional elements can be <tt>put</tt> without blocking. |
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* A <tt>BlockingQueue</tt> without any intrinsic capacity constraints always |
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* reports a remaining capacity of <tt>Integer.MAX_VALUE</tt>. |
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* |
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* <p> While <tt>BlockingQueue</tt> is designed to be used primarily |
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* for producer-consumer queues, it additionally supports the |
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* {@link java.util.Collection} interface. So, for example, it is possible to |
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* remove an arbitrary element from a queue using |
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* <tt>remove(x)</tt>. However, such operations are in general |
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* <em>NOT</em> performed very efficiently, and are intended for only |
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* occasional use, such as when a queued message is cancelled. Also, |
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* the bulk operations, most notably <tt>addAll</tt> are <em>NOT</em> |
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* performed atomically, so it is possible for <tt>addAll(c)</tt> to |
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* fail (throwing an exception) after adding only some of the elements |
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* in <tt>c</tt>. |
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* |
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* <p>A <tt>BlockingQueue</tt> does <em>not</em> intrinsically support |
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* any kind of "close" or "shutdown" operation to |
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* indicate that no more items will be added. The needs and usage of |
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* such features tend to be implementation-dependent. For example, a |
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* common tactic is for producers to insert special |
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* <em>end-of-stream</em> or <em>poison</em> objects, that are |
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* interpreted accordingly when taken by consumers. |
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* |
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* <p> |
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* Usage example, based on a typical producer-consumer scenario. |
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* Note that a <tt>BlockingQueue</tt> can safely be used with multiple |
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* producers and multiple consumers. |
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* <pre> |
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* class Producer implements Runnable { |
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* private final BlockingQueue queue; |
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* Producer(BlockingQueue q) { queue = q; } |
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* public void run() { |
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* try { |
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* while(true) { queue.put(produce()); } |
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* } catch (InterruptedException ex) { ... handle ...} |
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* } |
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* Object produce() { ... } |
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* } |
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* |
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* class Consumer implements Runnable { |
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* private final BlockingQueue queue; |
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* Concumer(BlockingQueue q) { queue = q; } |
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* public void run() { |
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* try { |
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* while(true) { consume(queue.take()); } |
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* } catch (InterruptedException ex) { ... handle ...} |
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* } |
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* void consume(Object x) { ... } |
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* } |
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* |
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* class Setup { |
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* void main() { |
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* BlockingQueue q = new SomeQueueImplementation(); |
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* Producer p = new Producer(q); |
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* Consumer c1 = new Consumer(q); |
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* Consumer c2 = new Consumer(q); |
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* new Thread(p).start(); |
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* new Thread(c1).start(); |
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* new Thread(c2).start(); |
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* } |
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* } |
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* </pre> |
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* |
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* |
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* @since 1.5 |
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* @author Doug Lea |
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*/ |
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public interface BlockingQueue<E> extends Queue<E> { |
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/** |
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* @throws IllegalStateException if this queue is full |
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* @throws NullPointerException if the specified element is <tt>null</tt>. |
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*/ |
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boolean add(E o); |
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/** |
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* @throws IllegalStateException if this queue is full |
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* @throws NullPointerException if <tt>c</tt> or any element of <tt>c<tt> |
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* is <tt>null</tt>. |
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*/ |
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boolean addAll(Collection<? extends E> c); |
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|
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/** |
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* @throws NullPointerException if the specified element is <tt>null</tt>. |
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*/ |
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boolean offer(E o); |
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|
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/** |
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* Adds the specified element to this queue, waiting if necessary up to the |
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* specified wait time for space to become available. |
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* @param o the element to add |
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* @param timeout how long to wait before giving up, in units of |
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* <tt>unit</tt> |
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* @param unit a <tt>TimeUnit</tt> determining how to interpret the |
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* <tt>timeout</tt> parameter |
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* @return <tt>true</tt> if successful, or <tt>false</tt> if |
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* the specified waiting time elapses before space is available. |
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* @throws InterruptedException if interrupted while waiting. |
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* @throws NullPointerException if the specified element is <tt>null</tt>. |
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*/ |
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boolean offer(E o, long timeout, TimeUnit unit) |
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throws InterruptedException; |
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|
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/** |
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* Retrieves and removes the head of this queue, waiting |
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* if necessary up to the specified wait time if no elements are |
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* present on this queue. |
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* @param timeout how long to wait before giving up, in units of |
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* <tt>unit</tt> |
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* @param unit a <tt>TimeUnit</tt> determining how to interpret the |
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* <tt>timeout</tt> parameter |
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* @return the head of this queue, or <tt>null</tt> if the |
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* specified waiting time elapses before an element is present. |
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* @throws InterruptedException if interrupted while waiting. |
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*/ |
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E poll(long timeout, TimeUnit unit) |
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throws InterruptedException; |
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|
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/** |
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* Retrieves and removes the head of this queue, waiting |
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* if no elements are present on this queue. |
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* @return the head of this queue |
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* @throws InterruptedException if interrupted while waiting. |
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*/ |
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E take() throws InterruptedException; |
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|
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/** |
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* Adds the specified element to this queue, waiting if necessary for |
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* space to become available. |
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* @param o the element to add |
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* @throws InterruptedException if interrupted while waiting. |
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* @throws NullPointerException if the specified element is <tt>null</tt>. |
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*/ |
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void put(E o) throws InterruptedException; |
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|
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/** |
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* Returns the number of elements that this queue can ideally (in |
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* the absence of memory or resource constraints) accept without |
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* blocking, or <tt>Integer.MAX_VALUE</tt> if there is no |
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* intrinsic limit. |
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* <p>Note that you <em>cannot</em> always tell if |
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* an attempt to <tt>add</tt> an element will succeed by |
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* inspecting <tt>remainingCapacity</tt> because it may be the |
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* case that a waiting consumer is ready to <tt>take</tt> an |
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* element out of an otherwise full queue. |
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* @return the remaining capacity |
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*/ |
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int remainingCapacity(); |
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} |
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