trunk/libjava/classpath/external/jsr166/java/util/concurrent/BlockingQueue.java

   1 /*
   2  * Written by Doug Lea with assistance from members of JCP JSR-166
   3  * Expert Group and released to the public domain, as explained at
   4  * http://creativecommons.org/licenses/publicdomain
   5  */
   6
   7 package java.util.concurrent;
   8
   9 import java.util.Collection;
  10 import java.util.Queue;
  11
  12 /**
  13  * A {@link java.util.Queue} that additionally supports operations
  14  * that wait for the queue to become non-empty when retrieving an
  15  * element, and wait for space to become available in the queue when
  16  * storing an element.
  17  *
  18  * <p><tt>BlockingQueue</tt> methods come in four forms, with different ways
  19  * of handling operations that cannot be satisfied immediately, but may be
  20  * satisfied at some point in the future:
  21  * one throws an exception, the second returns a special value (either
  22  * <tt>null</tt> or <tt>false</tt>, depending on the operation), the third
  23  * blocks the current thread indefinitely until the operation can succeed,
  24  * and the fourth blocks for only a given maximum time limit before giving
  25  * up.  These methods are summarized in the following table:
  26  *
  27  * <p>
  28  * <table BORDER CELLPADDING=3 CELLSPACING=1>
  29  *  <tr>
  30  *    <td></td>
  31  *    <td ALIGN=CENTER><em>Throws exception</em></td>
  32  *    <td ALIGN=CENTER><em>Special value</em></td>
  33  *    <td ALIGN=CENTER><em>Blocks</em></td>
  34  *    <td ALIGN=CENTER><em>Times out</em></td>
  35  *  </tr>
  36  *  <tr>
  37  *    <td><b>Insert</b></td>
  38  *    <td>{@link #add add(e)}</td>
  39  *    <td>{@link #offer offer(e)}</td>
  40  *    <td>{@link #put put(e)}</td>
  41  *    <td>{@link #offer(Object, long, TimeUnit) offer(e, time, unit)}</td>
  42  *  </tr>
  43  *  <tr>
  44  *    <td><b>Remove</b></td>
  45  *    <td>{@link #remove remove()}</td>
  46  *    <td>{@link #poll poll()}</td>
  47  *    <td>{@link #take take()}</td>
  48  *    <td>{@link #poll(long, TimeUnit) poll(time, unit)}</td>
  49  *  </tr>
  50  *  <tr>
  51  *    <td><b>Examine</b></td>
  52  *    <td>{@link #element element()}</td>
  53  *    <td>{@link #peek peek()}</td>
  54  *    <td><em>not applicable</em></td>
  55  *    <td><em>not applicable</em></td>
  56  *  </tr>
  57  * </table>
  58  *
  59  * <p>A <tt>BlockingQueue</tt> does not accept <tt>null</tt> elements.
  60  * Implementations throw <tt>NullPointerException</tt> on attempts
  61  * to <tt>add</tt>, <tt>put</tt> or <tt>offer</tt> a <tt>null</tt>.  A
  62  * <tt>null</tt> is used as a sentinel value to indicate failure of
  63  * <tt>poll</tt> operations.
  64  *
  65  * <p>A <tt>BlockingQueue</tt> may be capacity bounded. At any given
  66  * time it may have a <tt>remainingCapacity</tt> beyond which no
  67  * additional elements can be <tt>put</tt> without blocking.
  68  * A <tt>BlockingQueue</tt> without any intrinsic capacity constraints always
  69  * reports a remaining capacity of <tt>Integer.MAX_VALUE</tt>.
  70  *
  71  * <p> <tt>BlockingQueue</tt> implementations are designed to be used
  72  * primarily for producer-consumer queues, but additionally support
  73  * the {@link java.util.Collection} interface.  So, for example, it is
  74  * possible to remove an arbitrary element from a queue using
  75  * <tt>remove(x)</tt>. However, such operations are in general
  76  * <em>not</em> performed very efficiently, and are intended for only
  77  * occasional use, such as when a queued message is cancelled.
  78  *
  79  * <p> <tt>BlockingQueue</tt> implementations are thread-safe.  All
  80  * queuing methods achieve their effects atomically using internal
  81  * locks or other forms of concurrency control. However, the
  82  * <em>bulk</em> Collection operations <tt>addAll</tt>,
  83  * <tt>containsAll</tt>, <tt>retainAll</tt> and <tt>removeAll</tt> are
  84  * <em>not</em> necessarily performed atomically unless specified
  85  * otherwise in an implementation. So it is possible, for example, for
  86  * <tt>addAll(c)</tt> to fail (throwing an exception) after adding
  87  * only some of the elements in <tt>c</tt>.
  88  *
  89  * <p>A <tt>BlockingQueue</tt> does <em>not</em> intrinsically support
  90  * any kind of &quot;close&quot; or &quot;shutdown&quot; operation to
  91  * indicate that no more items will be added.  The needs and usage of
  92  * such features tend to be implementation-dependent. For example, a
  93  * common tactic is for producers to insert special
  94  * <em>end-of-stream</em> or <em>poison</em> objects, that are
  95  * interpreted accordingly when taken by consumers.
  96  *
  97  * <p>
  98  * Usage example, based on a typical producer-consumer scenario.
  99  * Note that a <tt>BlockingQueue</tt> can safely be used with multiple
 100  * producers and multiple consumers.
 101  * <pre>
 102  * class Producer implements Runnable {
 103  *   private final BlockingQueue queue;
 104  *   Producer(BlockingQueue q) { queue = q; }
 105  *   public void run() {
 106  *     try {
 107  *       while (true) { queue.put(produce()); }
 108  *     } catch (InterruptedException ex) { ... handle ...}
 109  *   }
 110  *   Object produce() { ... }
 111  * }
 112  *
 113  * class Consumer implements Runnable {
 114  *   private final BlockingQueue queue;
 115  *   Consumer(BlockingQueue q) { queue = q; }
 116  *   public void run() {
 117  *     try {
 118  *       while (true) { consume(queue.take()); }
 119  *     } catch (InterruptedException ex) { ... handle ...}
 120  *   }
 121  *   void consume(Object x) { ... }
 122  * }
 123  *
 124  * class Setup {
 125  *   void main() {
 126  *     BlockingQueue q = new SomeQueueImplementation();
 127  *     Producer p = new Producer(q);
 128  *     Consumer c1 = new Consumer(q);
 129  *     Consumer c2 = new Consumer(q);
 130  *     new Thread(p).start();
 131  *     new Thread(c1).start();
 132  *     new Thread(c2).start();
 133  *   }
 134  * }
 135  * </pre>
 136  *
 137  * <p>Memory consistency effects: As with other concurrent
 138  * collections, actions in a thread prior to placing an object into a
 139  * {@code BlockingQueue}
 140  * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
 141  * actions subsequent to the access or removal of that element from
 142  * the {@code BlockingQueue} in another thread.
 143  *
 144  * <p>This interface is a member of the
 145  * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 146  * Java Collections Framework</a>.
 147  *
 148  * @since 1.5
 149  * @author Doug Lea
 150  * @param <E> the type of elements held in this collection
 151  */
 152 public interface BlockingQueue<E> extends Queue<E> {
 153     /**
 154      * Inserts the specified element into this queue if it is possible to do
 155      * so immediately without violating capacity restrictions, returning
 156      * <tt>true</tt> upon success and throwing an
 157      * <tt>IllegalStateException</tt> if no space is currently available.
 158      * When using a capacity-restricted queue, it is generally preferable to
 159      * use {@link #offer(Object) offer}.
 160      *
 161      * @param e the element to add
 162      * @return <tt>true</tt> (as specified by {@link Collection#add})
 163      * @throws IllegalStateException if the element cannot be added at this
 164      *         time due to capacity restrictions
 165      * @throws ClassCastException if the class of the specified element
 166      *         prevents it from being added to this queue
 167      * @throws NullPointerException if the specified element is null
 168      * @throws IllegalArgumentException if some property of the specified
 169      *         element prevents it from being added to this queue
 170      */
 171     boolean add(E e);
 172
 173     /**
 174      * Inserts the specified element into this queue if it is possible to do
 175      * so immediately without violating capacity restrictions, returning
 176      * <tt>true</tt> upon success and <tt>false</tt> if no space is currently
 177      * available.  When using a capacity-restricted queue, this method is
 178      * generally preferable to {@link #add}, which can fail to insert an
 179      * element only by throwing an exception.
 180      *
 181      * @param e the element to add
 182      * @return <tt>true</tt> if the element was added to this queue, else
 183      *         <tt>false</tt>
 184      * @throws ClassCastException if the class of the specified element
 185      *         prevents it from being added to this queue
 186      * @throws NullPointerException if the specified element is null
 187      * @throws IllegalArgumentException if some property of the specified
 188      *         element prevents it from being added to this queue
 189      */
 190     boolean offer(E e);
 191
 192     /**
 193      * Inserts the specified element into this queue, waiting if necessary
 194      * for space to become available.
 195      *
 196      * @param e the element to add
 197      * @throws InterruptedException if interrupted while waiting
 198      * @throws ClassCastException if the class of the specified element
 199      *         prevents it from being added to this queue
 200      * @throws NullPointerException if the specified element is null
 201      * @throws IllegalArgumentException if some property of the specified
 202      *         element prevents it from being added to this queue
 203      */
 204     void put(E e) throws InterruptedException;
 205
 206     /**
 207      * Inserts the specified element into this queue, waiting up to the
 208      * specified wait time if necessary for space to become available.
 209      *
 210      * @param e the element to add
 211      * @param timeout how long to wait before giving up, in units of
 212      *        <tt>unit</tt>
 213      * @param unit a <tt>TimeUnit</tt> determining how to interpret the
 214      *        <tt>timeout</tt> parameter
 215      * @return <tt>true</tt> if successful, or <tt>false</tt> if
 216      *         the specified waiting time elapses before space is available
 217      * @throws InterruptedException if interrupted while waiting
 218      * @throws ClassCastException if the class of the specified element
 219      *         prevents it from being added to this queue
 220      * @throws NullPointerException if the specified element is null
 221      * @throws IllegalArgumentException if some property of the specified
 222      *         element prevents it from being added to this queue
 223      */
 224     boolean offer(E e, long timeout, TimeUnit unit)
 225         throws InterruptedException;
 226
 227     /**
 228      * Retrieves and removes the head of this queue, waiting if necessary
 229      * until an element becomes available.
 230      *
 231      * @return the head of this queue
 232      * @throws InterruptedException if interrupted while waiting
 233      */
 234     E take() throws InterruptedException;
 235
 236     /**
 237      * Retrieves and removes the head of this queue, waiting up to the
 238      * specified wait time if necessary for an element to become available.
 239      *
 240      * @param timeout how long to wait before giving up, in units of
 241      *        <tt>unit</tt>
 242      * @param unit a <tt>TimeUnit</tt> determining how to interpret the
 243      *        <tt>timeout</tt> parameter
 244      * @return the head of this queue, or <tt>null</tt> if the
 245      *         specified waiting time elapses before an element is available
 246      * @throws InterruptedException if interrupted while waiting
 247      */
 248     E poll(long timeout, TimeUnit unit)
 249         throws InterruptedException;
 250
 251     /**
 252      * Returns the number of additional elements that this queue can ideally
 253      * (in the absence of memory or resource constraints) accept without
 254      * blocking, or <tt>Integer.MAX_VALUE</tt> if there is no intrinsic
 255      * limit.
 256      *
 257      * <p>Note that you <em>cannot</em> always tell if an attempt to insert
 258      * an element will succeed by inspecting <tt>remainingCapacity</tt>
 259      * because it may be the case that another thread is about to
 260      * insert or remove an element.
 261      *
 262      * @return the remaining capacity
 263      */
 264     int remainingCapacity();
 265
 266     /**
 267      * Removes a single instance of the specified element from this queue,
 268      * if it is present.  More formally, removes an element <tt>e</tt> such
 269      * that <tt>o.equals(e)</tt>, if this queue contains one or more such
 270      * elements.
 271      * Returns <tt>true</tt> if this queue contained the specified element
 272      * (or equivalently, if this queue changed as a result of the call).
 273      *
 274      * @param o element to be removed from this queue, if present
 275      * @return <tt>true</tt> if this queue changed as a result of the call
 276      * @throws ClassCastException if the class of the specified element
 277      *         is incompatible with this queue (optional)
 278      * @throws NullPointerException if the specified element is null (optional)
 279      */
 280     boolean remove(Object o);
 281
 282     /**
 283      * Returns <tt>true</tt> if this queue contains the specified element.
 284      * More formally, returns <tt>true</tt> if and only if this queue contains
 285      * at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
 286      *
 287      * @param o object to be checked for containment in this queue
 288      * @return <tt>true</tt> if this queue contains the specified element
 289      * @throws ClassCastException if the class of the specified element
 290      *         is incompatible with this queue (optional)
 291      * @throws NullPointerException if the specified element is null (optional)
 292      */
 293     public boolean contains(Object o);
 294
 295     /**
 296      * Removes all available elements from this queue and adds them
 297      * to the given collection.  This operation may be more
 298      * efficient than repeatedly polling this queue.  A failure
 299      * encountered while attempting to add elements to
 300      * collection <tt>c</tt> may result in elements being in neither,
 301      * either or both collections when the associated exception is
 302      * thrown.  Attempts to drain a queue to itself result in
 303      * <tt>IllegalArgumentException</tt>. Further, the behavior of
 304      * this operation is undefined if the specified collection is
 305      * modified while the operation is in progress.
 306      *
 307      * @param c the collection to transfer elements into
 308      * @return the number of elements transferred
 309      * @throws UnsupportedOperationException if addition of elements
 310      *         is not supported by the specified collection
 311      * @throws ClassCastException if the class of an element of this queue
 312      *         prevents it from being added to the specified collection
 313      * @throws NullPointerException if the specified collection is null
 314      * @throws IllegalArgumentException if the specified collection is this
 315      *         queue, or some property of an element of this queue prevents
 316      *         it from being added to the specified collection
 317      */
 318     int drainTo(Collection<? super E> c);
 319
 320     /**
 321      * Removes at most the given number of available elements from
 322      * this queue and adds them to the given collection.  A failure
 323      * encountered while attempting to add elements to
 324      * collection <tt>c</tt> may result in elements being in neither,
 325      * either or both collections when the associated exception is
 326      * thrown.  Attempts to drain a queue to itself result in
 327      * <tt>IllegalArgumentException</tt>. Further, the behavior of
 328      * this operation is undefined if the specified collection is
 329      * modified while the operation is in progress.
 330      *
 331      * @param c the collection to transfer elements into
 332      * @param maxElements the maximum number of elements to transfer
 333      * @return the number of elements transferred
 334      * @throws UnsupportedOperationException if addition of elements
 335      *         is not supported by the specified collection
 336      * @throws ClassCastException if the class of an element of this queue
 337      *         prevents it from being added to the specified collection
 338      * @throws NullPointerException if the specified collection is null
 339      * @throws IllegalArgumentException if the specified collection is this
 340      *         queue, or some property of an element of this queue prevents
 341      *         it from being added to the specified collection
 342      */
 343     int drainTo(Collection<? super E> c, int maxElements);
 344 }