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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, as explained at |
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* http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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|
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package java.util.concurrent; |
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|
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import java.lang.invoke.MethodHandles; |
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import java.lang.invoke.VarHandle; |
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import java.util.ArrayList; |
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import java.util.List; |
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import java.util.concurrent.locks.LockSupport; |
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import java.util.function.BiConsumer; |
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import java.util.function.BiPredicate; |
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import java.util.function.Consumer; |
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|
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/** |
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* A {@link Flow.Publisher} that asynchronously issues submitted |
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* (non-null) items to current subscribers until it is closed. Each |
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* current subscriber receives newly submitted items in the same order |
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* unless drops or exceptions are encountered. Using a |
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* SubmissionPublisher allows item generators to act as compliant <a |
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* href="http://www.reactive-streams.org/"> reactive-streams</a> |
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* Publishers relying on drop handling and/or blocking for flow |
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* control. |
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* |
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* <p>A SubmissionPublisher uses the {@link Executor} supplied in its |
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* constructor for delivery to subscribers. The best choice of |
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* Executor depends on expected usage. If the generator(s) of |
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* submitted items run in separate threads, and the number of |
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* subscribers can be estimated, consider using a {@link |
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* Executors#newFixedThreadPool}. Otherwise consider using the |
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* default, normally the {@link ForkJoinPool#commonPool}. |
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* |
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* <p>Buffering allows producers and consumers to transiently operate |
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* at different rates. Each subscriber uses an independent buffer. |
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* Buffers are created upon first use and expanded as needed up to the |
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* given maximum. (The enforced capacity may be rounded up to the |
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* nearest power of two and/or bounded by the largest value supported |
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* by this implementation.) Invocations of {@link |
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* Flow.Subscription#request(long) request} do not directly result in |
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* buffer expansion, but risk saturation if unfilled requests exceed |
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* the maximum capacity. The default value of {@link |
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* Flow#defaultBufferSize()} may provide a useful starting point for |
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* choosing a capacity based on expected rates, resources, and usages. |
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* |
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* <p>Publication methods support different policies about what to do |
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* when buffers are saturated. Method {@link #submit(Object) submit} |
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* blocks until resources are available. This is simplest, but least |
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* responsive. The {@code offer} methods may drop items (either |
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* immediately or with bounded timeout), but provide an opportunity to |
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* interpose a handler and then retry. |
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* |
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* <p>If any Subscriber method throws an exception, its subscription |
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* is cancelled. If a handler is supplied as a constructor argument, |
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* it is invoked before cancellation upon an exception in method |
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* {@link Flow.Subscriber#onNext onNext}, but exceptions in methods |
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* {@link Flow.Subscriber#onSubscribe onSubscribe}, |
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* {@link Flow.Subscriber#onError(Throwable) onError} and |
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* {@link Flow.Subscriber#onComplete() onComplete} are not recorded or |
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* handled before cancellation. If the supplied Executor throws |
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* {@link RejectedExecutionException} (or any other RuntimeException |
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* or Error) when attempting to execute a task, or a drop handler |
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* throws an exception when processing a dropped item, then the |
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* exception is rethrown. In these cases, not all subscribers will |
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* have been issued the published item. It is usually good practice to |
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* {@link #closeExceptionally closeExceptionally} in these cases. |
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* |
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* <p>Method {@link #consume(Consumer)} simplifies support for a |
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* common case in which the only action of a subscriber is to request |
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* and process all items using a supplied function. |
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* |
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* <p>This class may also serve as a convenient base for subclasses |
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* that generate items, and use the methods in this class to publish |
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* them. For example here is a class that periodically publishes the |
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* items generated from a supplier. (In practice you might add methods |
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* to independently start and stop generation, to share Executors |
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* among publishers, and so on, or use a SubmissionPublisher as a |
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* component rather than a superclass.) |
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* |
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* <pre> {@code |
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* class PeriodicPublisher<T> extends SubmissionPublisher<T> { |
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* final ScheduledFuture<?> periodicTask; |
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* final ScheduledExecutorService scheduler; |
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* PeriodicPublisher(Executor executor, int maxBufferCapacity, |
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* Supplier<? extends T> supplier, |
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* long period, TimeUnit unit) { |
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* super(executor, maxBufferCapacity); |
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* scheduler = new ScheduledThreadPoolExecutor(1); |
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* periodicTask = scheduler.scheduleAtFixedRate( |
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* () -> submit(supplier.get()), 0, period, unit); |
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* } |
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* public void close() { |
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* periodicTask.cancel(false); |
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* scheduler.shutdown(); |
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* super.close(); |
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* } |
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* }}</pre> |
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* |
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* <p>Here is an example of a {@link Flow.Processor} implementation. |
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* It uses single-step requests to its publisher for simplicity of |
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* illustration. A more adaptive version could monitor flow using the |
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* lag estimate returned from {@code submit}, along with other utility |
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* methods. |
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* |
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* <pre> {@code |
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* class TransformProcessor<S,T> extends SubmissionPublisher<T> |
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* implements Flow.Processor<S,T> { |
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* final Function<? super S, ? extends T> function; |
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* Flow.Subscription subscription; |
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* TransformProcessor(Executor executor, int maxBufferCapacity, |
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* Function<? super S, ? extends T> function) { |
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* super(executor, maxBufferCapacity); |
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* this.function = function; |
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* } |
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* public void onSubscribe(Flow.Subscription subscription) { |
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* (this.subscription = subscription).request(1); |
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* } |
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* public void onNext(S item) { |
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* subscription.request(1); |
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* submit(function.apply(item)); |
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* } |
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* public void onError(Throwable ex) { closeExceptionally(ex); } |
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* public void onComplete() { close(); } |
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* }}</pre> |
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* |
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* @param <T> the published item type |
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* @author Doug Lea |
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* @since 9 |
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*/ |
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public class SubmissionPublisher<T> implements Flow.Publisher<T>, |
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AutoCloseable { |
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/* |
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* Most mechanics are handled by BufferedSubscription. This class |
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* mainly tracks subscribers and ensures sequentiality, by using |
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* built-in synchronization locks across public methods. (Using |
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* built-in locks works well in the most typical case in which |
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* only one thread submits items). |
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*/ |
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|
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/** The largest possible power of two array size. */ |
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static final int BUFFER_CAPACITY_LIMIT = 1 << 30; |
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|
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/** Round capacity to power of 2, at most limit. */ |
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static final int roundCapacity(int cap) { |
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int n = cap - 1; |
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n |= n >>> 1; |
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n |= n >>> 2; |
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n |= n >>> 4; |
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n |= n >>> 8; |
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n |= n >>> 16; |
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return (n <= 0) ? 1 : // at least 1 |
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(n >= BUFFER_CAPACITY_LIMIT) ? BUFFER_CAPACITY_LIMIT : n + 1; |
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} |
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|
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// default Executor setup; nearly the same as CompletableFuture |
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|
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/** |
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* Default executor -- ForkJoinPool.commonPool() unless it cannot |
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* support parallelism. |
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*/ |
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private static final Executor ASYNC_POOL = |
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(ForkJoinPool.getCommonPoolParallelism() > 1) ? |
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ForkJoinPool.commonPool() : new ThreadPerTaskExecutor(); |
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|
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/** Fallback if ForkJoinPool.commonPool() cannot support parallelism */ |
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private static final class ThreadPerTaskExecutor implements Executor { |
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ThreadPerTaskExecutor() {} // prevent access constructor creation |
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public void execute(Runnable r) { new Thread(r).start(); } |
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} |
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|
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/** |
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* Clients (BufferedSubscriptions) are maintained in a linked list |
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* (via their "next" fields). This works well for publish loops. |
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* It requires O(n) traversal to check for duplicate subscribers, |
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* but we expect that subscribing is much less common than |
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* publishing. Unsubscribing occurs only during traversal loops, |
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* when BufferedSubscription methods return negative values |
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* signifying that they have been disabled. To reduce |
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* head-of-line blocking, submit and offer methods first call |
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* BufferedSubscription.offer on each subscriber, and place |
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* saturated ones in retries list (using nextRetry field), and |
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* retry, possibly blocking or dropping. |
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*/ |
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BufferedSubscription<T> clients; |
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|
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/** Run status, updated only within locks */ |
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volatile boolean closed; |
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/** If non-null, the exception in closeExceptionally */ |
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volatile Throwable closedException; |
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|
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// Parameters for constructing BufferedSubscriptions |
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final Executor executor; |
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final BiConsumer<? super Flow.Subscriber<? super T>, ? super Throwable> onNextHandler; |
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final int maxBufferCapacity; |
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|
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/** |
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* Creates a new SubmissionPublisher using the given Executor for |
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* async delivery to subscribers, with the given maximum buffer size |
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* for each subscriber, and, if non-null, the given handler invoked |
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* when any Subscriber throws an exception in method {@link |
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* Flow.Subscriber#onNext(Object) onNext}. |
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* |
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* @param executor the executor to use for async delivery, |
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* supporting creation of at least one independent thread |
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* @param maxBufferCapacity the maximum capacity for each |
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* subscriber's buffer (the enforced capacity may be rounded up to |
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* the nearest power of two and/or bounded by the largest value |
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* supported by this implementation; method {@link #getMaxBufferCapacity} |
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* returns the actual value) |
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* @param handler if non-null, procedure to invoke upon exception |
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* thrown in method {@code onNext} |
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* @throws NullPointerException if executor is null |
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* @throws IllegalArgumentException if maxBufferCapacity not |
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* positive |
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*/ |
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public SubmissionPublisher(Executor executor, int maxBufferCapacity, |
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BiConsumer<? super Flow.Subscriber<? super T>, ? super Throwable> handler) { |
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if (executor == null) |
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throw new NullPointerException(); |
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if (maxBufferCapacity <= 0) |
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throw new IllegalArgumentException("capacity must be positive"); |
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this.executor = executor; |
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this.onNextHandler = handler; |
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this.maxBufferCapacity = roundCapacity(maxBufferCapacity); |
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} |
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|
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/** |
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* Creates a new SubmissionPublisher using the given Executor for |
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* async delivery to subscribers, with the given maximum buffer size |
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* for each subscriber, and no handler for Subscriber exceptions in |
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* method {@link Flow.Subscriber#onNext(Object) onNext}. |
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* |
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* @param executor the executor to use for async delivery, |
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* supporting creation of at least one independent thread |
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* @param maxBufferCapacity the maximum capacity for each |
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* subscriber's buffer (the enforced capacity may be rounded up to |
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* the nearest power of two and/or bounded by the largest value |
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* supported by this implementation; method {@link #getMaxBufferCapacity} |
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* returns the actual value) |
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* @throws NullPointerException if executor is null |
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* @throws IllegalArgumentException if maxBufferCapacity not |
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* positive |
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*/ |
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public SubmissionPublisher(Executor executor, int maxBufferCapacity) { |
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this(executor, maxBufferCapacity, null); |
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} |
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|
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/** |
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* Creates a new SubmissionPublisher using the {@link |
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* ForkJoinPool#commonPool()} for async delivery to subscribers |
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* (unless it does not support a parallelism level of at least two, |
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* in which case, a new Thread is created to run each task), with |
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* maximum buffer capacity of {@link Flow#defaultBufferSize}, and no |
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* handler for Subscriber exceptions in method {@link |
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* Flow.Subscriber#onNext(Object) onNext}. |
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*/ |
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public SubmissionPublisher() { |
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this(ASYNC_POOL, Flow.defaultBufferSize(), null); |
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} |
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|
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/** |
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* Adds the given Subscriber unless already subscribed. If already |
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* subscribed, the Subscriber's {@link |
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* Flow.Subscriber#onError(Throwable) onError} method is invoked on |
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* the existing subscription with an {@link IllegalStateException}. |
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* Otherwise, upon success, the Subscriber's {@link |
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* Flow.Subscriber#onSubscribe onSubscribe} method is invoked |
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* asynchronously with a new {@link Flow.Subscription}. If {@link |
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* Flow.Subscriber#onSubscribe onSubscribe} throws an exception, the |
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* subscription is cancelled. Otherwise, if this SubmissionPublisher |
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* was closed exceptionally, then the subscriber's {@link |
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* Flow.Subscriber#onError onError} method is invoked with the |
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* corresponding exception, or if closed without exception, the |
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* subscriber's {@link Flow.Subscriber#onComplete() onComplete} |
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* method is invoked. Subscribers may enable receiving items by |
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* invoking the {@link Flow.Subscription#request(long) request} |
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* method of the new Subscription, and may unsubscribe by invoking |
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* its {@link Flow.Subscription#cancel() cancel} method. |
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* |
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* @param subscriber the subscriber |
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* @throws NullPointerException if subscriber is null |
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*/ |
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public void subscribe(Flow.Subscriber<? super T> subscriber) { |
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if (subscriber == null) throw new NullPointerException(); |
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BufferedSubscription<T> subscription = |
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new BufferedSubscription<T>(subscriber, executor, |
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onNextHandler, maxBufferCapacity); |
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synchronized (this) { |
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for (BufferedSubscription<T> b = clients, pred = null;;) { |
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if (b == null) { |
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Throwable ex; |
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subscription.onSubscribe(); |
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if ((ex = closedException) != null) |
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subscription.onError(ex); |
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else if (closed) |
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subscription.onComplete(); |
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else if (pred == null) |
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clients = subscription; |
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else |
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pred.next = subscription; |
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break; |
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} |
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BufferedSubscription<T> next = b.next; |
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if (b.isDisabled()) { // remove |
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b.next = null; // detach |
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if (pred == null) |
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clients = next; |
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else |
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pred.next = next; |
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} |
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else if (subscriber.equals(b.subscriber)) { |
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b.onError(new IllegalStateException("Duplicate subscribe")); |
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break; |
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} |
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else |
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pred = b; |
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b = next; |
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} |
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} |
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} |
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|
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/** |
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* Publishes the given item to each current subscriber by |
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* asynchronously invoking its {@link Flow.Subscriber#onNext(Object) |
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* onNext} method, blocking uninterruptibly while resources for any |
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* subscriber are unavailable. This method returns an estimate of |
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* the maximum lag (number of items submitted but not yet consumed) |
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* among all current subscribers. This value is at least one |
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* (accounting for this submitted item) if there are any |
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* subscribers, else zero. |
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* |
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* <p>If the Executor for this publisher throws a |
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* RejectedExecutionException (or any other RuntimeException or |
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* Error) when attempting to asynchronously notify subscribers, |
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* then this exception is rethrown, in which case not all |
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* subscribers will have been issued this item. |
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* |
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* @param item the (non-null) item to publish |
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* @return the estimated maximum lag among subscribers |
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* @throws IllegalStateException if closed |
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* @throws NullPointerException if item is null |
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* @throws RejectedExecutionException if thrown by Executor |
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*/ |
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public int submit(T item) { |
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if (item == null) throw new NullPointerException(); |
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int lag = 0; |
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boolean complete; |
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synchronized (this) { |
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complete = closed; |
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BufferedSubscription<T> b = clients; |
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if (!complete) { |
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BufferedSubscription<T> pred = null, r = null, rtail = null; |
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while (b != null) { |
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BufferedSubscription<T> next = b.next; |
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int stat = b.offer(item); |
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if (stat < 0) { // disabled |
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b.next = null; |
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if (pred == null) |
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clients = next; |
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else |
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pred.next = next; |
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} |
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else { |
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if (stat > lag) |
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lag = stat; |
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else if (stat == 0) { // place on retry list |
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b.nextRetry = null; |
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if (rtail == null) |
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r = b; |
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else |
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rtail.nextRetry = b; |
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rtail = b; |
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} |
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pred = b; |
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} |
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b = next; |
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} |
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while (r != null) { |
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BufferedSubscription<T> nextRetry = r.nextRetry; |
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r.nextRetry = null; |
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int stat = r.submit(item); |
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if (stat > lag) |
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lag = stat; |
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else if (stat < 0 && clients == r) |
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clients = r.next; // postpone internal unsubscribes |
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r = nextRetry; |
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} |
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} |
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} |
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if (complete) |
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throw new IllegalStateException("Closed"); |
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else |
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return lag; |
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} |
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|
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/** |
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* Publishes the given item, if possible, to each current subscriber |
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* by asynchronously invoking its {@link |
401 |
* Flow.Subscriber#onNext(Object) onNext} method. The item may be |
402 |
* dropped by one or more subscribers if resource limits are |
403 |
* exceeded, in which case the given handler (if non-null) is |
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* invoked, and if it returns true, retried once. Other calls to |
405 |
* methods in this class by other threads are blocked while the |
406 |
* handler is invoked. Unless recovery is assured, options are |
407 |
* usually limited to logging the error and/or issuing an {@link |
408 |
* Flow.Subscriber#onError(Throwable) onError} signal to the |
409 |
* subscriber. |
410 |
* |
411 |
* <p>This method returns a status indicator: If negative, it |
412 |
* represents the (negative) number of drops (failed attempts to |
413 |
* issue the item to a subscriber). Otherwise it is an estimate of |
414 |
* the maximum lag (number of items submitted but not yet |
415 |
* consumed) among all current subscribers. This value is at least |
416 |
* one (accounting for this submitted item) if there are any |
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* subscribers, else zero. |
418 |
* |
419 |
* <p>If the Executor for this publisher throws a |
420 |
* RejectedExecutionException (or any other RuntimeException or |
421 |
* Error) when attempting to asynchronously notify subscribers, or |
422 |
* the drop handler throws an exception when processing a dropped |
423 |
* item, then this exception is rethrown. |
424 |
* |
425 |
* @param item the (non-null) item to publish |
426 |
* @param onDrop if non-null, the handler invoked upon a drop to a |
427 |
* subscriber, with arguments of the subscriber and item; if it |
428 |
* returns true, an offer is re-attempted (once) |
429 |
* @return if negative, the (negative) number of drops; otherwise |
430 |
* an estimate of maximum lag |
431 |
* @throws IllegalStateException if closed |
432 |
* @throws NullPointerException if item is null |
433 |
* @throws RejectedExecutionException if thrown by Executor |
434 |
*/ |
435 |
public int offer(T item, |
436 |
BiPredicate<Flow.Subscriber<? super T>, ? super T> onDrop) { |
437 |
return doOffer(0L, item, onDrop); |
438 |
} |
439 |
|
440 |
/** |
441 |
* Publishes the given item, if possible, to each current subscriber |
442 |
* by asynchronously invoking its {@link |
443 |
* Flow.Subscriber#onNext(Object) onNext} method, blocking while |
444 |
* resources for any subscription are unavailable, up to the |
445 |
* specified timeout or until the caller thread is interrupted, at |
446 |
* which point the given handler (if non-null) is invoked, and if it |
447 |
* returns true, retried once. (The drop handler may distinguish |
448 |
* timeouts from interrupts by checking whether the current thread |
449 |
* is interrupted.) Other calls to methods in this class by other |
450 |
* threads are blocked while the handler is invoked. Unless |
451 |
* recovery is assured, options are usually limited to logging the |
452 |
* error and/or issuing an {@link Flow.Subscriber#onError(Throwable) |
453 |
* onError} signal to the subscriber. |
454 |
* |
455 |
* <p>This method returns a status indicator: If negative, it |
456 |
* represents the (negative) number of drops (failed attempts to |
457 |
* issue the item to a subscriber). Otherwise it is an estimate of |
458 |
* the maximum lag (number of items submitted but not yet |
459 |
* consumed) among all current subscribers. This value is at least |
460 |
* one (accounting for this submitted item) if there are any |
461 |
* subscribers, else zero. |
462 |
* |
463 |
* <p>If the Executor for this publisher throws a |
464 |
* RejectedExecutionException (or any other RuntimeException or |
465 |
* Error) when attempting to asynchronously notify subscribers, or |
466 |
* the drop handler throws an exception when processing a dropped |
467 |
* item, then this exception is rethrown. |
468 |
* |
469 |
* @param item the (non-null) item to publish |
470 |
* @param timeout how long to wait for resources for any subscriber |
471 |
* before giving up, in units of {@code unit} |
472 |
* @param unit a {@code TimeUnit} determining how to interpret the |
473 |
* {@code timeout} parameter |
474 |
* @param onDrop if non-null, the handler invoked upon a drop to a |
475 |
* subscriber, with arguments of the subscriber and item; if it |
476 |
* returns true, an offer is re-attempted (once) |
477 |
* @return if negative, the (negative) number of drops; otherwise |
478 |
* an estimate of maximum lag |
479 |
* @throws IllegalStateException if closed |
480 |
* @throws NullPointerException if item is null |
481 |
* @throws RejectedExecutionException if thrown by Executor |
482 |
*/ |
483 |
public int offer(T item, long timeout, TimeUnit unit, |
484 |
BiPredicate<Flow.Subscriber<? super T>, ? super T> onDrop) { |
485 |
return doOffer(unit.toNanos(timeout), item, onDrop); |
486 |
} |
487 |
|
488 |
/** Common implementation for both forms of offer */ |
489 |
final int doOffer(long nanos, T item, |
490 |
BiPredicate<Flow.Subscriber<? super T>, ? super T> onDrop) { |
491 |
if (item == null) throw new NullPointerException(); |
492 |
int lag = 0, drops = 0; |
493 |
boolean complete; |
494 |
synchronized (this) { |
495 |
complete = closed; |
496 |
BufferedSubscription<T> b = clients; |
497 |
if (!complete) { |
498 |
BufferedSubscription<T> pred = null, r = null, rtail = null; |
499 |
while (b != null) { |
500 |
BufferedSubscription<T> next = b.next; |
501 |
int stat = b.offer(item); |
502 |
if (stat < 0) { |
503 |
b.next = null; |
504 |
if (pred == null) |
505 |
clients = next; |
506 |
else |
507 |
pred.next = next; |
508 |
} |
509 |
else { |
510 |
if (stat > lag) |
511 |
lag = stat; |
512 |
else if (stat == 0) { |
513 |
b.nextRetry = null; |
514 |
if (rtail == null) |
515 |
r = b; |
516 |
else |
517 |
rtail.nextRetry = b; |
518 |
rtail = b; |
519 |
} |
520 |
else if (stat > lag) |
521 |
lag = stat; |
522 |
pred = b; |
523 |
} |
524 |
b = next; |
525 |
} |
526 |
while (r != null) { |
527 |
BufferedSubscription<T> nextRetry = r.nextRetry; |
528 |
r.nextRetry = null; |
529 |
int stat = (nanos > 0L) |
530 |
? r.timedOffer(item, nanos) |
531 |
: r.offer(item); |
532 |
if (stat == 0 && onDrop != null && |
533 |
onDrop.test(r.subscriber, item)) |
534 |
stat = r.offer(item); |
535 |
if (stat == 0) |
536 |
++drops; |
537 |
else if (stat > lag) |
538 |
lag = stat; |
539 |
else if (stat < 0 && clients == r) |
540 |
clients = r.next; |
541 |
r = nextRetry; |
542 |
} |
543 |
} |
544 |
} |
545 |
if (complete) |
546 |
throw new IllegalStateException("Closed"); |
547 |
else |
548 |
return (drops > 0) ? -drops : lag; |
549 |
} |
550 |
|
551 |
/** |
552 |
* Unless already closed, issues {@link |
553 |
* Flow.Subscriber#onComplete() onComplete} signals to current |
554 |
* subscribers, and disallows subsequent attempts to publish. |
555 |
* Upon return, this method does <em>NOT</em> guarantee that all |
556 |
* subscribers have yet completed. |
557 |
*/ |
558 |
public void close() { |
559 |
if (!closed) { |
560 |
BufferedSubscription<T> b; |
561 |
synchronized (this) { |
562 |
b = clients; |
563 |
clients = null; |
564 |
closed = true; |
565 |
} |
566 |
while (b != null) { |
567 |
BufferedSubscription<T> next = b.next; |
568 |
b.next = null; |
569 |
b.onComplete(); |
570 |
b = next; |
571 |
} |
572 |
} |
573 |
} |
574 |
|
575 |
/** |
576 |
* Unless already closed, issues {@link |
577 |
* Flow.Subscriber#onError(Throwable) onError} signals to current |
578 |
* subscribers with the given error, and disallows subsequent |
579 |
* attempts to publish. Future subscribers also receive the given |
580 |
* error. Upon return, this method does <em>NOT</em> guarantee |
581 |
* that all subscribers have yet completed. |
582 |
* |
583 |
* @param error the {@code onError} argument sent to subscribers |
584 |
* @throws NullPointerException if error is null |
585 |
*/ |
586 |
public void closeExceptionally(Throwable error) { |
587 |
if (error == null) |
588 |
throw new NullPointerException(); |
589 |
if (!closed) { |
590 |
BufferedSubscription<T> b; |
591 |
synchronized (this) { |
592 |
b = clients; |
593 |
clients = null; |
594 |
if (!closed) // don't override plain close |
595 |
closedException = error; |
596 |
closed = true; |
597 |
} |
598 |
while (b != null) { |
599 |
BufferedSubscription<T> next = b.next; |
600 |
b.next = null; |
601 |
b.onError(error); |
602 |
b = next; |
603 |
} |
604 |
} |
605 |
} |
606 |
|
607 |
/** |
608 |
* Returns true if this publisher is not accepting submissions. |
609 |
* |
610 |
* @return true if closed |
611 |
*/ |
612 |
public boolean isClosed() { |
613 |
return closed; |
614 |
} |
615 |
|
616 |
/** |
617 |
* Returns the exception associated with {@link |
618 |
* #closeExceptionally(Throwable) closeExceptionally}, or null if |
619 |
* not closed or if closed normally. |
620 |
* |
621 |
* @return the exception, or null if none |
622 |
*/ |
623 |
public Throwable getClosedException() { |
624 |
return closedException; |
625 |
} |
626 |
|
627 |
/** |
628 |
* Returns true if this publisher has any subscribers. |
629 |
* |
630 |
* @return true if this publisher has any subscribers |
631 |
*/ |
632 |
public boolean hasSubscribers() { |
633 |
boolean nonEmpty = false; |
634 |
if (!closed) { |
635 |
synchronized (this) { |
636 |
for (BufferedSubscription<T> b = clients; b != null;) { |
637 |
BufferedSubscription<T> next = b.next; |
638 |
if (b.isDisabled()) { |
639 |
b.next = null; |
640 |
b = clients = next; |
641 |
} |
642 |
else { |
643 |
nonEmpty = true; |
644 |
break; |
645 |
} |
646 |
} |
647 |
} |
648 |
} |
649 |
return nonEmpty; |
650 |
} |
651 |
|
652 |
/** |
653 |
* Returns the number of current subscribers. |
654 |
* |
655 |
* @return the number of current subscribers |
656 |
*/ |
657 |
public int getNumberOfSubscribers() { |
658 |
int count = 0; |
659 |
if (!closed) { |
660 |
synchronized (this) { |
661 |
BufferedSubscription<T> pred = null, next; |
662 |
for (BufferedSubscription<T> b = clients; b != null; b = next) { |
663 |
next = b.next; |
664 |
if (b.isDisabled()) { |
665 |
b.next = null; |
666 |
if (pred == null) |
667 |
clients = next; |
668 |
else |
669 |
pred.next = next; |
670 |
} |
671 |
else { |
672 |
pred = b; |
673 |
++count; |
674 |
} |
675 |
} |
676 |
} |
677 |
} |
678 |
return count; |
679 |
} |
680 |
|
681 |
/** |
682 |
* Returns the Executor used for asynchronous delivery. |
683 |
* |
684 |
* @return the Executor used for asynchronous delivery |
685 |
*/ |
686 |
public Executor getExecutor() { |
687 |
return executor; |
688 |
} |
689 |
|
690 |
/** |
691 |
* Returns the maximum per-subscriber buffer capacity. |
692 |
* |
693 |
* @return the maximum per-subscriber buffer capacity |
694 |
*/ |
695 |
public int getMaxBufferCapacity() { |
696 |
return maxBufferCapacity; |
697 |
} |
698 |
|
699 |
/** |
700 |
* Returns a list of current subscribers for monitoring and |
701 |
* tracking purposes, not for invoking {@link Flow.Subscriber} |
702 |
* methods on the subscribers. |
703 |
* |
704 |
* @return list of current subscribers |
705 |
*/ |
706 |
public List<Flow.Subscriber<? super T>> getSubscribers() { |
707 |
ArrayList<Flow.Subscriber<? super T>> subs = new ArrayList<>(); |
708 |
synchronized (this) { |
709 |
BufferedSubscription<T> pred = null, next; |
710 |
for (BufferedSubscription<T> b = clients; b != null; b = next) { |
711 |
next = b.next; |
712 |
if (b.isDisabled()) { |
713 |
b.next = null; |
714 |
if (pred == null) |
715 |
clients = next; |
716 |
else |
717 |
pred.next = next; |
718 |
} |
719 |
else |
720 |
subs.add(b.subscriber); |
721 |
} |
722 |
} |
723 |
return subs; |
724 |
} |
725 |
|
726 |
/** |
727 |
* Returns true if the given Subscriber is currently subscribed. |
728 |
* |
729 |
* @param subscriber the subscriber |
730 |
* @return true if currently subscribed |
731 |
* @throws NullPointerException if subscriber is null |
732 |
*/ |
733 |
public boolean isSubscribed(Flow.Subscriber<? super T> subscriber) { |
734 |
if (subscriber == null) throw new NullPointerException(); |
735 |
if (!closed) { |
736 |
synchronized (this) { |
737 |
BufferedSubscription<T> pred = null, next; |
738 |
for (BufferedSubscription<T> b = clients; b != null; b = next) { |
739 |
next = b.next; |
740 |
if (b.isDisabled()) { |
741 |
b.next = null; |
742 |
if (pred == null) |
743 |
clients = next; |
744 |
else |
745 |
pred.next = next; |
746 |
} |
747 |
else if (subscriber.equals(b.subscriber)) |
748 |
return true; |
749 |
else |
750 |
pred = b; |
751 |
} |
752 |
} |
753 |
} |
754 |
return false; |
755 |
} |
756 |
|
757 |
/** |
758 |
* Returns an estimate of the minimum number of items requested |
759 |
* (via {@link Flow.Subscription#request(long) request}) but not |
760 |
* yet produced, among all current subscribers. |
761 |
* |
762 |
* @return the estimate, or zero if no subscribers |
763 |
*/ |
764 |
public long estimateMinimumDemand() { |
765 |
long min = Long.MAX_VALUE; |
766 |
boolean nonEmpty = false; |
767 |
synchronized (this) { |
768 |
BufferedSubscription<T> pred = null, next; |
769 |
for (BufferedSubscription<T> b = clients; b != null; b = next) { |
770 |
int n; long d; |
771 |
next = b.next; |
772 |
if ((n = b.estimateLag()) < 0) { |
773 |
b.next = null; |
774 |
if (pred == null) |
775 |
clients = next; |
776 |
else |
777 |
pred.next = next; |
778 |
} |
779 |
else { |
780 |
if ((d = b.demand - n) < min) |
781 |
min = d; |
782 |
nonEmpty = true; |
783 |
pred = b; |
784 |
} |
785 |
} |
786 |
} |
787 |
return nonEmpty ? min : 0; |
788 |
} |
789 |
|
790 |
/** |
791 |
* Returns an estimate of the maximum number of items produced but |
792 |
* not yet consumed among all current subscribers. |
793 |
* |
794 |
* @return the estimate |
795 |
*/ |
796 |
public int estimateMaximumLag() { |
797 |
int max = 0; |
798 |
synchronized (this) { |
799 |
BufferedSubscription<T> pred = null, next; |
800 |
for (BufferedSubscription<T> b = clients; b != null; b = next) { |
801 |
int n; |
802 |
next = b.next; |
803 |
if ((n = b.estimateLag()) < 0) { |
804 |
b.next = null; |
805 |
if (pred == null) |
806 |
clients = next; |
807 |
else |
808 |
pred.next = next; |
809 |
} |
810 |
else { |
811 |
if (n > max) |
812 |
max = n; |
813 |
pred = b; |
814 |
} |
815 |
} |
816 |
} |
817 |
return max; |
818 |
} |
819 |
|
820 |
/** |
821 |
* Processes all published items using the given Consumer function. |
822 |
* Returns a CompletableFuture that is completed normally when this |
823 |
* publisher signals {@link Flow.Subscriber#onComplete() |
824 |
* onComplete}, or completed exceptionally upon any error, or an |
825 |
* exception is thrown by the Consumer, or the returned |
826 |
* CompletableFuture is cancelled, in which case no further items |
827 |
* are processed. |
828 |
* |
829 |
* @param consumer the function applied to each onNext item |
830 |
* @return a CompletableFuture that is completed normally |
831 |
* when the publisher signals onComplete, and exceptionally |
832 |
* upon any error or cancellation |
833 |
* @throws NullPointerException if consumer is null |
834 |
*/ |
835 |
public CompletableFuture<Void> consume(Consumer<? super T> consumer) { |
836 |
if (consumer == null) |
837 |
throw new NullPointerException(); |
838 |
CompletableFuture<Void> status = new CompletableFuture<>(); |
839 |
subscribe(new ConsumerSubscriber<T>(status, consumer)); |
840 |
return status; |
841 |
} |
842 |
|
843 |
/** Subscriber for method consume */ |
844 |
private static final class ConsumerSubscriber<T> |
845 |
implements Flow.Subscriber<T> { |
846 |
final CompletableFuture<Void> status; |
847 |
final Consumer<? super T> consumer; |
848 |
Flow.Subscription subscription; |
849 |
ConsumerSubscriber(CompletableFuture<Void> status, |
850 |
Consumer<? super T> consumer) { |
851 |
this.status = status; this.consumer = consumer; |
852 |
} |
853 |
public final void onSubscribe(Flow.Subscription subscription) { |
854 |
this.subscription = subscription; |
855 |
status.whenComplete((v, e) -> subscription.cancel()); |
856 |
if (!status.isDone()) |
857 |
subscription.request(Long.MAX_VALUE); |
858 |
} |
859 |
public final void onError(Throwable ex) { |
860 |
status.completeExceptionally(ex); |
861 |
} |
862 |
public final void onComplete() { |
863 |
status.complete(null); |
864 |
} |
865 |
public final void onNext(T item) { |
866 |
try { |
867 |
consumer.accept(item); |
868 |
} catch (Throwable ex) { |
869 |
subscription.cancel(); |
870 |
status.completeExceptionally(ex); |
871 |
} |
872 |
} |
873 |
} |
874 |
|
875 |
/** |
876 |
* A task for consuming buffer items and signals, created and |
877 |
* executed whenever they become available. A task consumes as |
878 |
* many items/signals as possible before terminating, at which |
879 |
* point another task is created when needed. The dual Runnable |
880 |
* and ForkJoinTask declaration saves overhead when executed by |
881 |
* ForkJoinPools, without impacting other kinds of Executors. |
882 |
*/ |
883 |
@SuppressWarnings("serial") |
884 |
static final class ConsumerTask<T> extends ForkJoinTask<Void> |
885 |
implements Runnable, CompletableFuture.AsynchronousCompletionTask { |
886 |
final BufferedSubscription<T> consumer; |
887 |
ConsumerTask(BufferedSubscription<T> consumer) { |
888 |
this.consumer = consumer; |
889 |
} |
890 |
public final Void getRawResult() { return null; } |
891 |
public final void setRawResult(Void v) {} |
892 |
public final boolean exec() { consumer.consume(); return false; } |
893 |
public final void run() { consumer.consume(); } |
894 |
} |
895 |
|
896 |
/** |
897 |
* A bounded (ring) buffer with integrated control to start a |
898 |
* consumer task whenever items are available. The buffer |
899 |
* algorithm is similar to one used inside ForkJoinPool (see its |
900 |
* internal documentation for details) specialized for the case of |
901 |
* at most one concurrent producer and consumer, and power of two |
902 |
* buffer sizes. This allows methods to operate without locks even |
903 |
* while supporting resizing, blocking, task-triggering, and |
904 |
* garbage-free buffers (nulling out elements when consumed), |
905 |
* although supporting these does impose a bit of overhead |
906 |
* compared to plain fixed-size ring buffers. |
907 |
* |
908 |
* The publisher guarantees a single producer via its lock. We |
909 |
* ensure in this class that there is at most one consumer. The |
910 |
* request and cancel methods must be fully thread-safe but are |
911 |
* coded to exploit the most common case in which they are only |
912 |
* called by consumers (usually within onNext). |
913 |
* |
914 |
* Execution control is managed using the ACTIVE ctl bit. We |
915 |
* ensure that a task is active when consumable items (and |
916 |
* usually, SUBSCRIBE, ERROR or COMPLETE signals) are present and |
917 |
* there is demand (unfilled requests). This is complicated on |
918 |
* the creation side by the possibility of exceptions when trying |
919 |
* to execute tasks. These eventually force DISABLED state, but |
920 |
* sometimes not directly. On the task side, termination (clearing |
921 |
* ACTIVE) that would otherwise race with producers or request() |
922 |
* calls uses the CONSUME keep-alive bit to force a recheck. |
923 |
* |
924 |
* The ctl field also manages run state. When DISABLED, no further |
925 |
* updates are possible. Disabling may be preceded by setting |
926 |
* ERROR or COMPLETE (or both -- ERROR has precedence), in which |
927 |
* case the associated Subscriber methods are invoked, possibly |
928 |
* synchronously if there is no active consumer task (including |
929 |
* cases where execute() failed). The cancel() method is supported |
930 |
* by treating as ERROR but suppressing onError signal. |
931 |
* |
932 |
* Support for blocking also exploits the fact that there is only |
933 |
* one possible waiter. ManagedBlocker-compatible control fields |
934 |
* are placed in this class itself rather than in wait-nodes. |
935 |
* Blocking control relies on the "waiter" field. Producers set |
936 |
* the field before trying to block, but must then recheck (via |
937 |
* offer) before parking. Signalling then just unparks and clears |
938 |
* waiter field. If the producer and/or consumer are using a |
939 |
* ForkJoinPool, the producer attempts to help run consumer tasks |
940 |
* via ForkJoinPool.helpAsyncBlocker before blocking. |
941 |
* |
942 |
* This class uses @Contended and heuristic field declaration |
943 |
* ordering to reduce false-sharing-based memory contention among |
944 |
* instances of BufferedSubscription, but it does not currently |
945 |
* attempt to avoid memory contention among buffers. This field |
946 |
* and element packing can hurt performance especially when each |
947 |
* publisher has only one client operating at a high rate. |
948 |
* Addressing this may require allocating substantially more space |
949 |
* than users expect. |
950 |
*/ |
951 |
@SuppressWarnings("serial") |
952 |
@jdk.internal.vm.annotation.Contended |
953 |
private static final class BufferedSubscription<T> |
954 |
implements Flow.Subscription, ForkJoinPool.ManagedBlocker { |
955 |
// Order-sensitive field declarations |
956 |
long timeout; // > 0 if timed wait |
957 |
volatile long demand; // # unfilled requests |
958 |
int maxCapacity; // reduced on OOME |
959 |
int putStat; // offer result for ManagedBlocker |
960 |
volatile int ctl; // atomic run state flags |
961 |
volatile int head; // next position to take |
962 |
int tail; // next position to put |
963 |
Object[] array; // buffer: null if disabled |
964 |
Flow.Subscriber<? super T> subscriber; // null if disabled |
965 |
Executor executor; // null if disabled |
966 |
BiConsumer<? super Flow.Subscriber<? super T>, ? super Throwable> onNextHandler; |
967 |
volatile Throwable pendingError; // holds until onError issued |
968 |
volatile Thread waiter; // blocked producer thread |
969 |
T putItem; // for offer within ManagedBlocker |
970 |
BufferedSubscription<T> next; // used only by publisher |
971 |
BufferedSubscription<T> nextRetry; // used only by publisher |
972 |
|
973 |
// ctl values |
974 |
static final int ACTIVE = 0x01; // consumer task active |
975 |
static final int CONSUME = 0x02; // keep-alive for consumer task |
976 |
static final int DISABLED = 0x04; // final state |
977 |
static final int ERROR = 0x08; // signal onError then disable |
978 |
static final int SUBSCRIBE = 0x10; // signal onSubscribe |
979 |
static final int COMPLETE = 0x20; // signal onComplete when done |
980 |
|
981 |
static final long INTERRUPTED = -1L; // timeout vs interrupt sentinel |
982 |
|
983 |
/** |
984 |
* Initial buffer capacity used when maxBufferCapacity is |
985 |
* greater. Must be a power of two. |
986 |
*/ |
987 |
static final int DEFAULT_INITIAL_CAP = 32; |
988 |
|
989 |
BufferedSubscription(Flow.Subscriber<? super T> subscriber, |
990 |
Executor executor, |
991 |
BiConsumer<? super Flow.Subscriber<? super T>, |
992 |
? super Throwable> onNextHandler, |
993 |
int maxBufferCapacity) { |
994 |
this.subscriber = subscriber; |
995 |
this.executor = executor; |
996 |
this.onNextHandler = onNextHandler; |
997 |
this.maxCapacity = maxBufferCapacity; |
998 |
this.array = new Object[maxBufferCapacity < DEFAULT_INITIAL_CAP ? |
999 |
(maxBufferCapacity < 2 ? // at least 2 slots |
1000 |
2 : maxBufferCapacity) : |
1001 |
DEFAULT_INITIAL_CAP]; |
1002 |
} |
1003 |
|
1004 |
final boolean isDisabled() { |
1005 |
return ctl == DISABLED; |
1006 |
} |
1007 |
|
1008 |
/** |
1009 |
* Returns estimated number of buffered items, or -1 if |
1010 |
* disabled. |
1011 |
*/ |
1012 |
final int estimateLag() { |
1013 |
int n; |
1014 |
return (ctl == DISABLED) ? -1 : ((n = tail - head) > 0) ? n : 0; |
1015 |
} |
1016 |
|
1017 |
/** |
1018 |
* Tries to add item and start consumer task if necessary. |
1019 |
* @return -1 if disabled, 0 if dropped, else estimated lag |
1020 |
*/ |
1021 |
final int offer(T item) { |
1022 |
int h = head, t = tail, cap, size, stat; |
1023 |
Object[] a = array; |
1024 |
if (a != null && (cap = a.length) > 0 && cap >= (size = t + 1 - h)) { |
1025 |
a[(cap - 1) & t] = item; // relaxed writes OK |
1026 |
tail = t + 1; |
1027 |
stat = size; |
1028 |
} |
1029 |
else |
1030 |
stat = growAndAdd(a, item); |
1031 |
return (stat > 0 && |
1032 |
(ctl & (ACTIVE | CONSUME)) != (ACTIVE | CONSUME)) ? |
1033 |
startOnOffer(stat) : stat; |
1034 |
} |
1035 |
|
1036 |
/** |
1037 |
* Tries to create or expand buffer, then adds item if possible. |
1038 |
*/ |
1039 |
private int growAndAdd(Object[] a, T item) { |
1040 |
boolean alloc; |
1041 |
int cap, stat; |
1042 |
if ((ctl & (ERROR | DISABLED)) != 0) { |
1043 |
cap = 0; |
1044 |
stat = -1; |
1045 |
alloc = false; |
1046 |
} |
1047 |
else if (a == null || (cap = a.length) <= 0) { |
1048 |
cap = 0; |
1049 |
stat = 1; |
1050 |
alloc = true; |
1051 |
} |
1052 |
else { |
1053 |
VarHandle.fullFence(); // recheck |
1054 |
int h = head, t = tail, size = t + 1 - h; |
1055 |
if (cap >= size) { |
1056 |
a[(cap - 1) & t] = item; |
1057 |
tail = t + 1; |
1058 |
stat = size; |
1059 |
alloc = false; |
1060 |
} |
1061 |
else if (cap >= maxCapacity) { |
1062 |
stat = 0; // cannot grow |
1063 |
alloc = false; |
1064 |
} |
1065 |
else { |
1066 |
stat = cap + 1; |
1067 |
alloc = true; |
1068 |
} |
1069 |
} |
1070 |
if (alloc) { |
1071 |
int newCap = (cap > 0) ? cap << 1 : 1; |
1072 |
if (newCap <= cap) |
1073 |
stat = 0; |
1074 |
else { |
1075 |
Object[] newArray = null; |
1076 |
try { |
1077 |
newArray = new Object[newCap]; |
1078 |
} catch (Throwable ex) { // try to cope with OOME |
1079 |
} |
1080 |
if (newArray == null) { |
1081 |
if (cap > 0) |
1082 |
maxCapacity = cap; // avoid continuous failure |
1083 |
stat = 0; |
1084 |
} |
1085 |
else { |
1086 |
array = newArray; |
1087 |
int t = tail; |
1088 |
int newMask = newCap - 1; |
1089 |
if (a != null && cap > 0) { |
1090 |
int mask = cap - 1; |
1091 |
for (int j = head; j != t; ++j) { |
1092 |
int k = j & mask; |
1093 |
Object x = QA.getAcquire(a, k); |
1094 |
if (x != null && // races with consumer |
1095 |
QA.compareAndSet(a, k, x, null)) |
1096 |
newArray[j & newMask] = x; |
1097 |
} |
1098 |
} |
1099 |
newArray[t & newMask] = item; |
1100 |
tail = t + 1; |
1101 |
} |
1102 |
} |
1103 |
} |
1104 |
return stat; |
1105 |
} |
1106 |
|
1107 |
/** |
1108 |
* Spins/helps/blocks while offer returns 0. Called only if |
1109 |
* initial offer return 0. |
1110 |
*/ |
1111 |
final int submit(T item) { |
1112 |
int stat; |
1113 |
if ((stat = offer(item)) == 0) { |
1114 |
putItem = item; |
1115 |
timeout = 0L; |
1116 |
putStat = 0; |
1117 |
ForkJoinPool.helpAsyncBlocker(executor, this); |
1118 |
if ((stat = putStat) == 0) { |
1119 |
try { |
1120 |
ForkJoinPool.managedBlock(this); |
1121 |
} catch (InterruptedException ie) { |
1122 |
timeout = INTERRUPTED; |
1123 |
} |
1124 |
stat = putStat; |
1125 |
} |
1126 |
if (timeout < 0L) |
1127 |
Thread.currentThread().interrupt(); |
1128 |
} |
1129 |
return stat; |
1130 |
} |
1131 |
|
1132 |
/** |
1133 |
* Timeout version; similar to submit. |
1134 |
*/ |
1135 |
final int timedOffer(T item, long nanos) { |
1136 |
int stat; |
1137 |
if ((stat = offer(item)) == 0 && (timeout = nanos) > 0L) { |
1138 |
putItem = item; |
1139 |
putStat = 0; |
1140 |
ForkJoinPool.helpAsyncBlocker(executor, this); |
1141 |
if ((stat = putStat) == 0) { |
1142 |
try { |
1143 |
ForkJoinPool.managedBlock(this); |
1144 |
} catch (InterruptedException ie) { |
1145 |
timeout = INTERRUPTED; |
1146 |
} |
1147 |
stat = putStat; |
1148 |
} |
1149 |
if (timeout < 0L) |
1150 |
Thread.currentThread().interrupt(); |
1151 |
} |
1152 |
return stat; |
1153 |
} |
1154 |
|
1155 |
/** |
1156 |
* Tries to start consumer task after offer. |
1157 |
* @return -1 if now disabled, else argument |
1158 |
*/ |
1159 |
private int startOnOffer(int stat) { |
1160 |
for (;;) { |
1161 |
Executor e; int c; |
1162 |
if ((c = ctl) == DISABLED || (e = executor) == null) { |
1163 |
stat = -1; |
1164 |
break; |
1165 |
} |
1166 |
else if ((c & ACTIVE) != 0) { // ensure keep-alive |
1167 |
if ((c & CONSUME) != 0 || |
1168 |
CTL.compareAndSet(this, c, c | CONSUME)) |
1169 |
break; |
1170 |
} |
1171 |
else if (demand == 0L || tail == head) |
1172 |
break; |
1173 |
else if (CTL.compareAndSet(this, c, c | (ACTIVE | CONSUME))) { |
1174 |
try { |
1175 |
e.execute(new ConsumerTask<T>(this)); |
1176 |
break; |
1177 |
} catch (RuntimeException | Error ex) { // back out |
1178 |
do {} while (((c = ctl) & DISABLED) == 0 && |
1179 |
(c & ACTIVE) != 0 && |
1180 |
!CTL.weakCompareAndSet |
1181 |
(this, c, c & ~ACTIVE)); |
1182 |
throw ex; |
1183 |
} |
1184 |
} |
1185 |
} |
1186 |
return stat; |
1187 |
} |
1188 |
|
1189 |
private void signalWaiter(Thread w) { |
1190 |
waiter = null; |
1191 |
LockSupport.unpark(w); // release producer |
1192 |
} |
1193 |
|
1194 |
/** |
1195 |
* Nulls out most fields, mainly to avoid garbage retention |
1196 |
* until publisher unsubscribes, but also to help cleanly stop |
1197 |
* upon error by nulling required components. |
1198 |
*/ |
1199 |
private void detach() { |
1200 |
Thread w = waiter; |
1201 |
executor = null; |
1202 |
subscriber = null; |
1203 |
pendingError = null; |
1204 |
signalWaiter(w); |
1205 |
} |
1206 |
|
1207 |
/** |
1208 |
* Issues error signal, asynchronously if a task is running, |
1209 |
* else synchronously. |
1210 |
*/ |
1211 |
final void onError(Throwable ex) { |
1212 |
for (int c;;) { |
1213 |
if (((c = ctl) & (ERROR | DISABLED)) != 0) |
1214 |
break; |
1215 |
else if ((c & ACTIVE) != 0) { |
1216 |
pendingError = ex; |
1217 |
if (CTL.compareAndSet(this, c, c | ERROR)) |
1218 |
break; // cause consumer task to exit |
1219 |
} |
1220 |
else if (CTL.compareAndSet(this, c, DISABLED)) { |
1221 |
Flow.Subscriber<? super T> s = subscriber; |
1222 |
if (s != null && ex != null) { |
1223 |
try { |
1224 |
s.onError(ex); |
1225 |
} catch (Throwable ignore) { |
1226 |
} |
1227 |
} |
1228 |
detach(); |
1229 |
break; |
1230 |
} |
1231 |
} |
1232 |
} |
1233 |
|
1234 |
/** |
1235 |
* Tries to start consumer task upon a signal or request; |
1236 |
* disables on failure. |
1237 |
*/ |
1238 |
private void startOrDisable() { |
1239 |
Executor e; |
1240 |
if ((e = executor) != null) { // skip if already disabled |
1241 |
try { |
1242 |
e.execute(new ConsumerTask<T>(this)); |
1243 |
} catch (Throwable ex) { // back out and force signal |
1244 |
for (int c;;) { |
1245 |
if ((c = ctl) == DISABLED || (c & ACTIVE) == 0) |
1246 |
break; |
1247 |
if (CTL.compareAndSet(this, c, c & ~ACTIVE)) { |
1248 |
onError(ex); |
1249 |
break; |
1250 |
} |
1251 |
} |
1252 |
} |
1253 |
} |
1254 |
} |
1255 |
|
1256 |
final void onComplete() { |
1257 |
for (int c;;) { |
1258 |
if ((c = ctl) == DISABLED) |
1259 |
break; |
1260 |
if (CTL.compareAndSet(this, c, |
1261 |
c | (ACTIVE | CONSUME | COMPLETE))) { |
1262 |
if ((c & ACTIVE) == 0) |
1263 |
startOrDisable(); |
1264 |
break; |
1265 |
} |
1266 |
} |
1267 |
} |
1268 |
|
1269 |
final void onSubscribe() { |
1270 |
for (int c;;) { |
1271 |
if ((c = ctl) == DISABLED) |
1272 |
break; |
1273 |
if (CTL.compareAndSet(this, c, |
1274 |
c | (ACTIVE | CONSUME | SUBSCRIBE))) { |
1275 |
if ((c & ACTIVE) == 0) |
1276 |
startOrDisable(); |
1277 |
break; |
1278 |
} |
1279 |
} |
1280 |
} |
1281 |
|
1282 |
/** |
1283 |
* Causes consumer task to exit if active (without reporting |
1284 |
* onError unless there is already a pending error), and |
1285 |
* disables. |
1286 |
*/ |
1287 |
public void cancel() { |
1288 |
for (int c;;) { |
1289 |
if ((c = ctl) == DISABLED) |
1290 |
break; |
1291 |
else if ((c & ACTIVE) != 0) { |
1292 |
if (CTL.compareAndSet(this, c, |
1293 |
c | (CONSUME | ERROR))) |
1294 |
break; |
1295 |
} |
1296 |
else if (CTL.compareAndSet(this, c, DISABLED)) { |
1297 |
detach(); |
1298 |
break; |
1299 |
} |
1300 |
} |
1301 |
} |
1302 |
|
1303 |
/** |
1304 |
* Adds to demand and possibly starts task. |
1305 |
*/ |
1306 |
public void request(long n) { |
1307 |
if (n > 0L) { |
1308 |
for (;;) { |
1309 |
long prev = demand, d; |
1310 |
if ((d = prev + n) < prev) // saturate |
1311 |
d = Long.MAX_VALUE; |
1312 |
if (DEMAND.compareAndSet(this, prev, d)) { |
1313 |
for (int c, h;;) { |
1314 |
if ((c = ctl) == DISABLED) |
1315 |
break; |
1316 |
else if ((c & ACTIVE) != 0) { |
1317 |
if ((c & CONSUME) != 0 || |
1318 |
CTL.compareAndSet(this, c, c | CONSUME)) |
1319 |
break; |
1320 |
} |
1321 |
else if ((h = head) != tail) { |
1322 |
if (CTL.compareAndSet(this, c, |
1323 |
c | (ACTIVE|CONSUME))) { |
1324 |
startOrDisable(); |
1325 |
break; |
1326 |
} |
1327 |
} |
1328 |
else if (head == h && tail == h) |
1329 |
break; // else stale |
1330 |
if (demand == 0L) |
1331 |
break; |
1332 |
} |
1333 |
break; |
1334 |
} |
1335 |
} |
1336 |
} |
1337 |
else if (n < 0L) |
1338 |
onError(new IllegalArgumentException( |
1339 |
"negative subscription request")); |
1340 |
} |
1341 |
|
1342 |
public final boolean isReleasable() { // for ManagedBlocker |
1343 |
T item = putItem; |
1344 |
if (item != null) { |
1345 |
if ((putStat = offer(item)) == 0) |
1346 |
return false; |
1347 |
putItem = null; |
1348 |
} |
1349 |
return true; |
1350 |
} |
1351 |
|
1352 |
public final boolean block() { // for ManagedBlocker |
1353 |
T item = putItem; |
1354 |
if (item != null) { |
1355 |
putItem = null; |
1356 |
long nanos = timeout; |
1357 |
long deadline = (nanos > 0L) ? System.nanoTime() + nanos : 0L; |
1358 |
while ((putStat = offer(item)) == 0) { |
1359 |
if (Thread.interrupted()) { |
1360 |
timeout = INTERRUPTED; |
1361 |
if (nanos > 0L) |
1362 |
break; |
1363 |
} |
1364 |
else if (nanos > 0L && |
1365 |
(nanos = deadline - System.nanoTime()) <= 0L) |
1366 |
break; |
1367 |
else if (waiter == null) |
1368 |
waiter = Thread.currentThread(); |
1369 |
else { |
1370 |
if (nanos > 0L) |
1371 |
LockSupport.parkNanos(this, nanos); |
1372 |
else |
1373 |
LockSupport.park(this); |
1374 |
waiter = null; |
1375 |
} |
1376 |
} |
1377 |
} |
1378 |
waiter = null; |
1379 |
return true; |
1380 |
} |
1381 |
|
1382 |
/** |
1383 |
* Consumer loop, called from ConsumerTask, or indirectly |
1384 |
* when helping during submit. |
1385 |
*/ |
1386 |
final void consume() { |
1387 |
Flow.Subscriber<? super T> s; |
1388 |
int h = head; |
1389 |
if ((s = subscriber) != null) { // else disabled |
1390 |
for (;;) { |
1391 |
long d = demand; |
1392 |
int c; Object[] a; int n, i; Object x; Thread w; |
1393 |
if (((c = ctl) & (ERROR | SUBSCRIBE | DISABLED)) != 0) { |
1394 |
if (!checkControl(s, c)) |
1395 |
break; |
1396 |
} |
1397 |
else if ((a = array) == null || h == tail || |
1398 |
(n = a.length) == 0 || |
1399 |
(x = QA.getAcquire(a, i = (n - 1) & h)) == null) { |
1400 |
if (!checkEmpty(s, c)) |
1401 |
break; |
1402 |
} |
1403 |
else if (d == 0L) { |
1404 |
if (!checkDemand(c)) |
1405 |
break; |
1406 |
} |
1407 |
else if (((c & CONSUME) != 0 || |
1408 |
CTL.compareAndSet(this, c, c | CONSUME)) && |
1409 |
QA.compareAndSet(a, i, x, null)) { |
1410 |
HEAD.setRelease(this, ++h); |
1411 |
DEMAND.getAndAdd(this, -1L); |
1412 |
if ((w = waiter) != null) |
1413 |
signalWaiter(w); |
1414 |
try { |
1415 |
@SuppressWarnings("unchecked") T y = (T) x; |
1416 |
s.onNext(y); |
1417 |
} catch (Throwable ex) { |
1418 |
handleOnNext(s, ex); |
1419 |
} |
1420 |
} |
1421 |
} |
1422 |
} |
1423 |
} |
1424 |
|
1425 |
/** |
1426 |
* Responds to control events in consume(). |
1427 |
*/ |
1428 |
private boolean checkControl(Flow.Subscriber<? super T> s, int c) { |
1429 |
boolean stat = true; |
1430 |
if ((c & SUBSCRIBE) != 0) { |
1431 |
if (CTL.compareAndSet(this, c, c & ~SUBSCRIBE)) { |
1432 |
try { |
1433 |
if (s != null) |
1434 |
s.onSubscribe(this); |
1435 |
} catch (Throwable ex) { |
1436 |
onError(ex); |
1437 |
} |
1438 |
} |
1439 |
} |
1440 |
else if ((c & ERROR) != 0) { |
1441 |
Throwable ex = pendingError; |
1442 |
ctl = DISABLED; // no need for CAS |
1443 |
if (ex != null) { // null if errorless cancel |
1444 |
try { |
1445 |
if (s != null) |
1446 |
s.onError(ex); |
1447 |
} catch (Throwable ignore) { |
1448 |
} |
1449 |
} |
1450 |
} |
1451 |
else { |
1452 |
detach(); |
1453 |
stat = false; |
1454 |
} |
1455 |
return stat; |
1456 |
} |
1457 |
|
1458 |
/** |
1459 |
* Responds to apparent emptiness in consume(). |
1460 |
*/ |
1461 |
private boolean checkEmpty(Flow.Subscriber<? super T> s, int c) { |
1462 |
boolean stat = true; |
1463 |
if (head == tail) { |
1464 |
if ((c & CONSUME) != 0) |
1465 |
CTL.compareAndSet(this, c, c & ~CONSUME); |
1466 |
else if ((c & COMPLETE) != 0) { |
1467 |
if (CTL.compareAndSet(this, c, DISABLED)) { |
1468 |
try { |
1469 |
if (s != null) |
1470 |
s.onComplete(); |
1471 |
} catch (Throwable ignore) { |
1472 |
} |
1473 |
} |
1474 |
} |
1475 |
else if (CTL.compareAndSet(this, c, c & ~ACTIVE)) |
1476 |
stat = false; |
1477 |
} |
1478 |
return stat; |
1479 |
} |
1480 |
|
1481 |
/** |
1482 |
* Responds to apparent zero demand in consume(). |
1483 |
*/ |
1484 |
private boolean checkDemand(int c) { |
1485 |
boolean stat = true; |
1486 |
if (demand == 0L) { |
1487 |
if ((c & CONSUME) != 0) |
1488 |
CTL.compareAndSet(this, c, c & ~CONSUME); |
1489 |
else if (CTL.compareAndSet(this, c, c & ~ACTIVE)) |
1490 |
stat = false; |
1491 |
} |
1492 |
return stat; |
1493 |
} |
1494 |
|
1495 |
/** |
1496 |
* Processes exception in Subscriber.onNext. |
1497 |
*/ |
1498 |
private void handleOnNext(Flow.Subscriber<? super T> s, Throwable ex) { |
1499 |
BiConsumer<? super Flow.Subscriber<? super T>, ? super Throwable> h; |
1500 |
if ((h = onNextHandler) != null) { |
1501 |
try { |
1502 |
h.accept(s, ex); |
1503 |
} catch (Throwable ignore) { |
1504 |
} |
1505 |
} |
1506 |
onError(ex); |
1507 |
} |
1508 |
|
1509 |
// VarHandle mechanics |
1510 |
private static final VarHandle CTL; |
1511 |
private static final VarHandle TAIL; |
1512 |
private static final VarHandle HEAD; |
1513 |
private static final VarHandle DEMAND; |
1514 |
private static final VarHandle QA; |
1515 |
|
1516 |
static { |
1517 |
try { |
1518 |
MethodHandles.Lookup l = MethodHandles.lookup(); |
1519 |
CTL = l.findVarHandle(BufferedSubscription.class, "ctl", |
1520 |
int.class); |
1521 |
TAIL = l.findVarHandle(BufferedSubscription.class, "tail", |
1522 |
int.class); |
1523 |
HEAD = l.findVarHandle(BufferedSubscription.class, "head", |
1524 |
int.class); |
1525 |
DEMAND = l.findVarHandle(BufferedSubscription.class, "demand", |
1526 |
long.class); |
1527 |
QA = MethodHandles.arrayElementVarHandle(Object[].class); |
1528 |
} catch (ReflectiveOperationException e) { |
1529 |
throw new Error(e); |
1530 |
} |
1531 |
|
1532 |
// Reduce the risk of rare disastrous classloading in first call to |
1533 |
// LockSupport.park: https://bugs.openjdk.java.net/browse/JDK-8074773 |
1534 |
Class<?> ensureLoaded = LockSupport.class; |
1535 |
} |
1536 |
} |
1537 |
} |