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Diffstat (limited to 'luni/src/main/java/java/util/concurrent/TransferQueue.java')
| -rw-r--r-- | luni/src/main/java/java/util/concurrent/TransferQueue.java | 133 |
1 files changed, 133 insertions, 0 deletions
diff --git a/luni/src/main/java/java/util/concurrent/TransferQueue.java b/luni/src/main/java/java/util/concurrent/TransferQueue.java new file mode 100644 index 0000000..9cd5773 --- /dev/null +++ b/luni/src/main/java/java/util/concurrent/TransferQueue.java @@ -0,0 +1,133 @@ +/* + * 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/publicdomain/zero/1.0/ + */ + +package java.util.concurrent; + +// BEGIN android-note +// removed link to collections framework docs +// END android-note + +/** + * A {@link BlockingQueue} in which producers may wait for consumers + * to receive elements. A {@code TransferQueue} may be useful for + * example in message passing applications in which producers + * sometimes (using method {@link #transfer}) await receipt of + * elements by consumers invoking {@code take} or {@code poll}, while + * at other times enqueue elements (via method {@code put}) without + * waiting for receipt. + * {@linkplain #tryTransfer(Object) Non-blocking} and + * {@linkplain #tryTransfer(Object,long,TimeUnit) time-out} versions of + * {@code tryTransfer} are also available. + * A {@code TransferQueue} may also be queried, via {@link + * #hasWaitingConsumer}, whether there are any threads waiting for + * items, which is a converse analogy to a {@code peek} operation. + * + * <p>Like other blocking queues, a {@code TransferQueue} may be + * capacity bounded. If so, an attempted transfer operation may + * initially block waiting for available space, and/or subsequently + * block waiting for reception by a consumer. Note that in a queue + * with zero capacity, such as {@link SynchronousQueue}, {@code put} + * and {@code transfer} are effectively synonymous. + * + * @since 1.7 + * @hide + * @author Doug Lea + * @param <E> the type of elements held in this collection + */ +public interface TransferQueue<E> extends BlockingQueue<E> { + /** + * Transfers the element to a waiting consumer immediately, if possible. + * + * <p>More precisely, transfers the specified element immediately + * if there exists a consumer already waiting to receive it (in + * {@link #take} or timed {@link #poll(long,TimeUnit) poll}), + * otherwise returning {@code false} without enqueuing the element. + * + * @param e the element to transfer + * @return {@code true} if the element was transferred, else + * {@code false} + * @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 tryTransfer(E e); + + /** + * Transfers the element to a consumer, waiting if necessary to do so. + * + * <p>More precisely, transfers the specified element immediately + * if there exists a consumer already waiting to receive it (in + * {@link #take} or timed {@link #poll(long,TimeUnit) poll}), + * else waits until the element is received by a consumer. + * + * @param e the element to transfer + * @throws InterruptedException if interrupted while waiting, + * in which case the element is not left enqueued + * @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 transfer(E e) throws InterruptedException; + + /** + * Transfers the element to a consumer if it is possible to do so + * before the timeout elapses. + * + * <p>More precisely, transfers the specified element immediately + * if there exists a consumer already waiting to receive it (in + * {@link #take} or timed {@link #poll(long,TimeUnit) poll}), + * else waits until the element is received by a consumer, + * returning {@code false} if the specified wait time elapses + * before the element can be transferred. + * + * @param e the element to transfer + * @param timeout how long to wait before giving up, in units of + * {@code unit} + * @param unit a {@code TimeUnit} determining how to interpret the + * {@code timeout} parameter + * @return {@code true} if successful, or {@code false} if + * the specified waiting time elapses before completion, + * in which case the element is not left enqueued + * @throws InterruptedException if interrupted while waiting, + * in which case the element is not left enqueued + * @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 tryTransfer(E e, long timeout, TimeUnit unit) + throws InterruptedException; + + /** + * Returns {@code true} if there is at least one consumer waiting + * to receive an element via {@link #take} or + * timed {@link #poll(long,TimeUnit) poll}. + * The return value represents a momentary state of affairs. + * + * @return {@code true} if there is at least one waiting consumer + */ + boolean hasWaitingConsumer(); + + /** + * Returns an estimate of the number of consumers waiting to + * receive elements via {@link #take} or timed + * {@link #poll(long,TimeUnit) poll}. The return value is an + * approximation of a momentary state of affairs, that may be + * inaccurate if consumers have completed or given up waiting. + * The value may be useful for monitoring and heuristics, but + * not for synchronization control. Implementations of this + * method are likely to be noticeably slower than those for + * {@link #hasWaitingConsumer}. + * + * @return the number of consumers waiting to receive elements + */ + int getWaitingConsumerCount(); +} |