IBlockingQueue Interface

Definition

[Android.Runtime.Register("java/util/concurrent/BlockingQueue", "", "Java.Util.Concurrent.IBlockingQueueInvoker")]
[Java.Interop.JavaTypeParameters(new System.String[] { "E" })]
public interface IBlockingQueue : IDisposable, Java.Interop.IJavaPeerable, Java.Util.IQueue

[<Android.Runtime.Register("java/util/concurrent/BlockingQueue", "", "Java.Util.Concurrent.IBlockingQueueInvoker")>]
[<Java.Interop.JavaTypeParameters(new System.String[] { "E" })>]
type IBlockingQueue = interface
    interface IQueue
    interface ICollection
    interface IIterable
    interface IJavaObject
    interface IDisposable
    interface IJavaPeerable

Derived

Java.Util.Concurrent.ArrayBlockingQueue

Java.Util.Concurrent.DelayQueue

Java.Util.Concurrent.IBlockingDeque

Java.Util.Concurrent.ITransferQueue

Java.Util.Concurrent.LinkedBlockingDeque

More…

Attributes

RegisterAttribute JavaTypeParametersAttribute

Implements

IJavaObject IJavaPeerable IIterable ICollection IQueue IDisposable

Remarks

A 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.

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 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:

<table class="plain"> <caption>Summary of BlockingQueue methods</caption> <tr> <td></td> <th scope="col" style="font-weight:normal; font-style:italic">Throws exception</th> <th scope="col" style="font-weight:normal; font-style:italic">Special value</th> <th scope="col" style="font-weight:normal; font-style:italic">Blocks</th> <th scope="col" style="font-weight:normal; font-style:italic">Times out</th> </tr> <tr> <th scope="row" style="text-align:left">Insert</th> <td>#add(Object) add(e)</td> <td>#offer(Object) offer(e)</td> <td>#put(Object) put(e)</td> <td>#offer(Object, long, TimeUnit) offer(e, time, unit)</td> </tr> <tr> <th scope="row" style="text-align:left">Remove</th> <td>#remove() remove()</td> <td>#poll() poll()</td> <td>#take() take()</td> <td>#poll(long, TimeUnit) poll(time, unit)</td> </tr> <tr> <th scope="row" style="text-align:left">Examine</th> <td>#element() element()</td> <td>#peek() peek()</td> <td style="font-style: italic">not applicable</td> <td style="font-style: italic">not applicable</td> </tr> </table>

A BlockingQueue does not accept null elements. Implementations throw NullPointerException on attempts to add, put or offer a null. A null is used as a sentinel value to indicate failure of poll operations.

A BlockingQueue may be capacity bounded. At any given time it may have a remainingCapacity beyond which no additional elements can be put without blocking. A BlockingQueue without any intrinsic capacity constraints always reports a remaining capacity of Integer.MAX_VALUE.

BlockingQueue implementations are designed to be used primarily for producer-consumer queues, but additionally support the Collection interface. So, for example, it is possible to remove an arbitrary element from a queue using remove(x). 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.

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</em> Collection operations addAll, containsAll, retainAll and removeAll are <em>not</em> necessarily performed atomically unless specified otherwise in an implementation. So it is possible, for example, for addAll(c) to fail (throwing an exception) after adding only some of the elements in c.

A BlockingQueue does <em>not</em> intrinsically support any kind of &quot;close&quot; or &quot;shutdown&quot; 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.

Usage example, based on a typical producer-consumer scenario. Note that a BlockingQueue can safely be used with multiple producers and multiple consumers.

{@code
            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();
              }
            }}

Memory consistency effects: As with other concurrent collections, actions in a thread prior to placing an object into a BlockingQueue<i>happen-before</i> actions subsequent to the access or removal of that element from the BlockingQueue in another thread.

This interface is a member of the Java Collections Framework.

Added in 1.5.

Java documentation for java.util.concurrent.BlockingQueue.

Portions of this page are modifications based on work created and shared by the Android Open Source Project and used according to terms described in the Creative Commons 2.5 Attribution License.

Properties

Methods

Explicit Interface Implementations

Extension Methods

Applies to