| /* |
| * 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 java.util.concurrent; |
| |
| import java.util.Collection; |
| import java.util.Queue; |
| |
| // BEGIN android-note |
| // removed link to collections framework docs |
| // END android-note |
| |
| /** |
| * 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(E, 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. |
| * |
| * @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(E) 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); |
| } |
