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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.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.BiPredicate; |
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import java.util.function.Function; |
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import java.util.function.Supplier; |
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|
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/** |
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* A {@link Flow.Publisher} that asynchronously issues submitted items |
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* to current subscribers until it is closed. Each current subscriber |
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* receives newly submitted items in the same order unless drops or |
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* exceptions are encountered. Using a SubmissionPublisher allows |
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* item generators to act as Publishers relying on drop handling |
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* and/or blocking for flow 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 a |
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* work-stealing pool (including {@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 with a given initial capacity, |
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* and are resized as needed up to the maximum. (Capacity arguments |
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* may be rounded up to powers of two.) Invocations of {@link |
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* Flow.Subscription#request} do not directly result in buffer |
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* expansion, but risk saturation if unfulfilled requests exceed the |
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* maximum capacity. Choices of buffer parameters rely on expected |
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* rates, resources, and usages, that usually benefit from empirical |
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* testing. As first guesses, consider initial 8 and maximum 1024. |
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* |
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* <p>An overloaded version of method {@code subscribe} allows |
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* subscribers to override executor and buffer parameters for |
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* a new subscription. |
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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} blocks until |
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* 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 the supplied Executor throws |
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* RejectedExecutionException (or any other RuntimeException or Error) |
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* when attempting to execute a task, or a drop handler throws an |
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* exception when processing a dropped item, then the exception is |
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* rethrown. In these cases, some but not all subscribers may have |
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* received items. It is usually good practice to {@link |
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* #closeExceptionally closeExceptionally} in these cases. |
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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 schedulers |
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* among publishers, and so on, or instead use a SubmissionPublisher |
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* as a 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 initialBufferCapacity, |
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* int maxBufferCapacity, Supplier<? extends T> supplier, |
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* long period, TimeUnit unit) { |
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* super(executor, initialBufferCapacity, 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 {@link Flow.Processor} subclass (using |
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* single-step requests to its publisher, for simplicity of |
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* illustration): |
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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 initialBufferCapacity, |
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* int maxBufferCapacity, |
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* Function<? super S, ? extends T> function) { |
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* super(executor, initialBufferCapacity, 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 1.9 |
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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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// Ensuring that all arrays have power of two length |
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|
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static final int MAXIMUM_BUFFER_CAPACITY = 1 << 30; |
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static final int roundCapacity(int cap) { // to nearest power of 2 |
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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 : |
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(n >= MAXIMUM_BUFFER_CAPACITY) ? MAXIMUM_BUFFER_CAPACITY : n + 1; |
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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 or status checks return |
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* negative values signifying that they have been disabled. |
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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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|
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// Parameters for constructing BufferedSubscriptions |
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final Executor executor; |
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final int minBufferCapacity; |
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final int maxBufferCapacity; |
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|
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/** |
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* Screens user arguments |
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*/ |
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static void checkParams(Executor executor, |
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int initialBufferCapacity, |
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int maxBufferCapacity) { |
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if (executor == null) |
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throw new NullPointerException(); |
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if (initialBufferCapacity <= 0 || maxBufferCapacity <= 0) |
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throw new IllegalArgumentException("capacity must be positive"); |
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if (maxBufferCapacity > MAXIMUM_BUFFER_CAPACITY) |
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throw new IllegalArgumentException("capacity exceeds limit"); |
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if (initialBufferCapacity > maxBufferCapacity) |
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throw new IllegalArgumentException("initial cannot exceed max capacity"); |
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} |
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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, and with the given initial and |
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* maximum buffer sizes for each subscriber. In the absence of |
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* other constraints, consider using {@code |
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* ForkJoinPool.commonPool(), 8, 1024}. |
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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 initialBufferCapacity the initial capacity for each |
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* subscriber's buffer (the actual capacity may be rounded up to |
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* the nearest power of two) |
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* @param maxBufferCapacity the maximum capacity for each |
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* subscriber's buffer (the actual capacity may be rounded up to |
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* the nearest power of two) |
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* @throws NullPointerException if executor is null |
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* @throws IllegalArgumentException if initialBufferCapacity is |
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* not positive or exceeds maxBufferCapacity, or maxBufferCapacity |
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* exceeds {@code 1<<30} (about 1 billion), the maximum bound for |
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* a power of two array size |
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*/ |
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public SubmissionPublisher(Executor executor, |
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int initialBufferCapacity, |
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int maxBufferCapacity) { |
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checkParams(executor, initialBufferCapacity, maxBufferCapacity); |
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int minc = roundCapacity(initialBufferCapacity); |
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int maxc = roundCapacity(maxBufferCapacity); |
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this.executor = executor; |
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this.minBufferCapacity = minc; |
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this.maxBufferCapacity = maxc; |
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} |
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|
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/** |
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* Adds the given Subscriber unless already subscribed. If |
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* already subscribed, the Subscriber's onError method is invoked |
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* with an IllegalStateException. Otherwise, upon success, the |
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* Subscriber's onSubscribe method is invoked with a new |
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* Subscription. If onSubscribe throws an exception, the |
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* subscription is cancelled. Otherwise, if this |
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* SubmissionPublisher is closed, the subscriber's onComplete |
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* method is then invoked. Subscribers may enable receiving items |
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* by invoking the {@code request} method of the new Subscription, |
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* and may unsubscribe by invoking its 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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doSubscribe(subscriber, executor, minBufferCapacity, maxBufferCapacity); |
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} |
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|
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/** |
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* Adds the given subscriber, with the same effects as {@link |
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* #subscribe(Flow.Subscriber)}, but overriding the |
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* executor and/or buffer capacities otherwise used by this |
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* Publisher. |
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* |
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* @param subscriber the subscriber |
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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 initialBufferCapacity the initial capacity for each |
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* subscriber's buffer (the actual capacity may be rounded up to |
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* the nearest power of two) |
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* @param maxBufferCapacity the maximum capacity for each |
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* subscriber's buffer (the actual capacity may be rounded up to |
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* the nearest power of two) |
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* @throws NullPointerException if executor or subscriber are null |
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* @throws IllegalArgumentException if initialBufferCapacity is |
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* not positive or exceeds maxBufferCapacity, or maxBufferCapacity |
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* exceeds {@code 1<<30} (about 1 billion), the maximum bound for |
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* a power of two array size |
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*/ |
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public void subscribe(Flow.Subscriber<? super T> subscriber, |
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Executor executor, |
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int initialBufferCapacity, |
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int maxBufferCapacity) { |
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checkParams(executor, initialBufferCapacity, maxBufferCapacity); |
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doSubscribe(subscriber, executor, |
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roundCapacity(initialBufferCapacity), |
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roundCapacity(maxBufferCapacity)); |
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} |
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|
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/** |
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* Implements both forms of subscribe |
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*/ |
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final void doSubscribe(Flow.Subscriber<? super T> subscriber, |
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Executor e, int minCap, int maxCap) { |
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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, e, minCap, maxCap); |
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boolean present = false, complete; |
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synchronized (this) { |
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complete = closed; |
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BufferedSubscription<T> pred = null, next; |
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for (BufferedSubscription<T> b = clients; ; b = next) { |
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if (b == null) { |
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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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subscription.onSubscribe(); |
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break; |
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} |
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next = b.next; |
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if (b.isDisabled()) { // remove |
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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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present = true; |
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break; |
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} |
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pred = b; |
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} |
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} |
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if (present) |
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subscriber.onError(new IllegalStateException("Already subscribed")); |
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else if (complete) |
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subscription.onComplete(); |
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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 onNext method, blocking |
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* uninterruptibly while resources for any subscriber are |
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* unavailable. |
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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 |
311 |
* Error) when attempting to asynchronously notify subscribers, |
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* then this exception is rethrown. |
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* |
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* @param item the (non-null) item to publish |
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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 void submit(T item) { |
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if (item == null) throw new NullPointerException(); |
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synchronized (this) { |
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if (closed) |
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throw new IllegalStateException("Closed"); |
324 |
BufferedSubscription<T> pred = null, next; |
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for (BufferedSubscription<T> b = clients; b != null; b = next) { |
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int stat; |
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next = b.next; |
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if ((stat = b.submit(item)) < 0) { |
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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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pred = b; |
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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, if possible, to each current |
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* subscriber by asynchronously invoking its onNext method. The |
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* item may be dropped by one or more subscribers if resource |
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* limits are exceeded, in which case the given handler (if |
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* non-null) is invoked, and if it returns true, retried once. |
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* Other calls to methods in this class by other threads are |
347 |
* blocked while the handler is invoked. Unless recovery is |
348 |
* assured, options are usually limited to logging the error |
349 |
* and/or issuing an onError signal to the subscriber. |
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* |
351 |
* <p>If the Executor for this publisher throws a |
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* RejectedExecutionException (or any other RuntimeException or |
353 |
* Error) when attempting to asynchronously notify subscribers, or |
354 |
* the drop handler throws an exception when processing a dropped |
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* item, then this exception is rethrown. |
356 |
* |
357 |
* @param item the (non-null) item to publish |
358 |
* @param onDrop if non-null, the handler invoked upon a drop to a |
359 |
* subscriber, with arguments of the subscriber and item; if it |
360 |
* returns true, an offer is re-attempted (once) |
361 |
* @return the number of drops (failed attempts to issue the item |
362 |
* to a subscriber) |
363 |
* @throws IllegalStateException if closed |
364 |
* @throws NullPointerException if item is null |
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* @throws RejectedExecutionException if thrown by Executor |
366 |
*/ |
367 |
public int offer(T item, |
368 |
BiPredicate<Flow.Subscriber<? super T>, ? super T> onDrop) { |
369 |
if (item == null) throw new NullPointerException(); |
370 |
int drops = 0; |
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synchronized (this) { |
372 |
if (closed) |
373 |
throw new IllegalStateException("Closed"); |
374 |
BufferedSubscription<T> pred = null, next; |
375 |
for (BufferedSubscription<T> b = clients; b != null; b = next) { |
376 |
int stat; |
377 |
next = b.next; |
378 |
if ((stat = b.offer(item)) == 0 && |
379 |
onDrop != null && |
380 |
onDrop.test(b.subscriber, item)) |
381 |
stat = b.offer(item); |
382 |
if (stat < 0) { |
383 |
if (pred == null) |
384 |
clients = next; |
385 |
else |
386 |
pred.next = next; |
387 |
} |
388 |
else { |
389 |
pred = b; |
390 |
if (stat == 0) |
391 |
++drops; |
392 |
} |
393 |
} |
394 |
return drops; |
395 |
} |
396 |
} |
397 |
|
398 |
/** |
399 |
* Publishes the given item, if possible, to each current |
400 |
* subscriber by asynchronously invoking its onNext method, |
401 |
* blocking while resources for any subscription are unavailable, |
402 |
* up to the specified timeout or the caller thread is |
403 |
* interrupted, at which point the given handler (if non-null) is |
404 |
* invoked, and if it returns true, retried once. (The drop |
405 |
* handler may distinguish timeouts from interrupts by checking |
406 |
* whether the current thread is interrupted.) Other calls to |
407 |
* methods in this class by other threads are blocked while the |
408 |
* handler is invoked. Unless recovery is assured, options are |
409 |
* usually limited to logging the error and/or issuing an onError |
410 |
* signal to the subscriber. |
411 |
* |
412 |
* <p>If the Executor for this publisher throws a |
413 |
* RejectedExecutionException (or any other RuntimeException or |
414 |
* Error) when attempting to asynchronously notify subscribers, or |
415 |
* the drop handler throws an exception when processing a dropped |
416 |
* item, then this exception is rethrown. |
417 |
* |
418 |
* @param item the (non-null) item to publish |
419 |
* @param timeout how long to wait for resources for any subscriber |
420 |
* before giving up, in units of {@code unit} |
421 |
* @param unit a {@code TimeUnit} determining how to interpret the |
422 |
* {@code timeout} parameter |
423 |
* @param onDrop if non-null, the handler invoked upon a drop to a |
424 |
* subscriber, with arguments of the subscriber and item; if it |
425 |
* returns true, an offer is re-attempted (once) |
426 |
* @return the number of drops (failed attempts to issue the item |
427 |
* to a subscriber) |
428 |
* @throws IllegalStateException if closed |
429 |
* @throws NullPointerException if item is null |
430 |
* @throws RejectedExecutionException if thrown by Executor |
431 |
*/ |
432 |
public int offer(T item, long timeout, TimeUnit unit, |
433 |
BiPredicate<Flow.Subscriber<? super T>, ? super T> onDrop) { |
434 |
if (item == null) throw new NullPointerException(); |
435 |
long nanos = unit.toNanos(timeout); |
436 |
int drops = 0; |
437 |
synchronized (this) { |
438 |
if (closed) |
439 |
throw new IllegalStateException("Closed"); |
440 |
BufferedSubscription<T> pred = null, next; |
441 |
for (BufferedSubscription<T> b = clients; b != null; b = next) { |
442 |
int stat; |
443 |
next = b.next; |
444 |
if ((stat = b.offerNanos(item, nanos)) == 0 && |
445 |
onDrop != null && onDrop.test(b.subscriber, item)) |
446 |
stat = b.offer(item); |
447 |
if (stat < 0) { |
448 |
if (pred == null) |
449 |
clients = next; |
450 |
else |
451 |
pred.next = next; |
452 |
} |
453 |
else { |
454 |
pred = b; |
455 |
if (stat == 0) |
456 |
++drops; |
457 |
} |
458 |
} |
459 |
} |
460 |
return drops; |
461 |
} |
462 |
|
463 |
/** |
464 |
* Unless already closed, issues onComplete signals to current |
465 |
* subscribers, and disallows subsequent attempts to publish. |
466 |
*/ |
467 |
public void close() { |
468 |
if (!closed) { |
469 |
BufferedSubscription<T> b, next; |
470 |
synchronized (this) { |
471 |
b = clients; |
472 |
clients = null; |
473 |
closed = true; |
474 |
} |
475 |
while (b != null) { |
476 |
next = b.next; |
477 |
b.onComplete(); |
478 |
b = next; |
479 |
} |
480 |
} |
481 |
} |
482 |
|
483 |
/** |
484 |
* Unless already closed, issues onError signals to current |
485 |
* subscribers with the given error, and disallows subsequent |
486 |
* attempts to publish. |
487 |
* |
488 |
* @param error the onError argument sent to subscribers |
489 |
* @throws NullPointerException if error is null |
490 |
*/ |
491 |
public void closeExceptionally(Throwable error) { |
492 |
if (error == null) |
493 |
throw new NullPointerException(); |
494 |
if (!closed) { |
495 |
BufferedSubscription<T> b, next; |
496 |
synchronized (this) { |
497 |
b = clients; |
498 |
clients = null; |
499 |
closed = true; |
500 |
} |
501 |
while (b != null) { |
502 |
next = b.next; |
503 |
b.onError(error); |
504 |
b = next; |
505 |
} |
506 |
} |
507 |
} |
508 |
|
509 |
/** |
510 |
* Returns true if this publisher is not accepting submissions. |
511 |
* |
512 |
* @return true if closed |
513 |
*/ |
514 |
public boolean isClosed() { |
515 |
return closed; |
516 |
} |
517 |
|
518 |
/** |
519 |
* Returns true if this publisher has any subscribers. |
520 |
* |
521 |
* @return true if this publisher has any subscribers |
522 |
*/ |
523 |
public boolean hasSubscribers() { |
524 |
boolean nonEmpty = false; |
525 |
if (!closed) { |
526 |
synchronized (this) { |
527 |
BufferedSubscription<T> pred = null, next; |
528 |
for (BufferedSubscription<T> b = clients; b != null; b = next) { |
529 |
next = b.next; |
530 |
if (b.isDisabled()) { |
531 |
if (pred == null) |
532 |
clients = next; |
533 |
else |
534 |
pred.next = next; |
535 |
} |
536 |
else { |
537 |
nonEmpty = true; |
538 |
break; |
539 |
} |
540 |
} |
541 |
} |
542 |
} |
543 |
return nonEmpty; |
544 |
} |
545 |
|
546 |
/** |
547 |
* Returns the Executor used for asynchronous delivery. |
548 |
* |
549 |
* @return the Executor used for asynchronous delivery |
550 |
*/ |
551 |
public Executor getExecutor() { |
552 |
return executor; |
553 |
} |
554 |
|
555 |
/** |
556 |
* Returns the initial per-subscriber buffer capacity. |
557 |
* |
558 |
* @return the initial per-subscriber buffer capacity |
559 |
*/ |
560 |
public int getInitialBufferCapacity() { |
561 |
return minBufferCapacity; |
562 |
} |
563 |
|
564 |
/** |
565 |
* Returns the maximum per-subscriber buffer capacity. |
566 |
* |
567 |
* @return the maximum per-subscriber buffer capacity |
568 |
*/ |
569 |
public int getMaxBufferCapacity() { |
570 |
return maxBufferCapacity; |
571 |
} |
572 |
|
573 |
/** |
574 |
* Returns a list of current subscribers. |
575 |
* |
576 |
* @return list of current subscribers |
577 |
*/ |
578 |
public List<Flow.Subscriber<? super T>> getSubscribers() { |
579 |
ArrayList<Flow.Subscriber<? super T>> subs = new ArrayList<>(); |
580 |
synchronized (this) { |
581 |
BufferedSubscription<T> pred = null, next; |
582 |
for (BufferedSubscription<T> b = clients; b != null; b = next) { |
583 |
next = b.next; |
584 |
if (b.isDisabled()) { |
585 |
if (pred == null) |
586 |
clients = next; |
587 |
else |
588 |
pred.next = next; |
589 |
} |
590 |
else |
591 |
subs.add(b.subscriber); |
592 |
} |
593 |
} |
594 |
return subs; |
595 |
} |
596 |
|
597 |
/** |
598 |
* Returns true if the given Subscriber is currently subscribed. |
599 |
* |
600 |
* @param subscriber the subscriber |
601 |
* @return true if currently subscribed |
602 |
*/ |
603 |
public boolean isSubscribed(Flow.Subscriber<? super T> subscriber) { |
604 |
if (!closed) { |
605 |
synchronized (this) { |
606 |
BufferedSubscription<T> pred = null, next; |
607 |
for (BufferedSubscription<T> b = clients; b != null; b = next) { |
608 |
next = b.next; |
609 |
if (b.isDisabled()) { |
610 |
if (pred == null) |
611 |
clients = next; |
612 |
else |
613 |
pred.next = next; |
614 |
} |
615 |
else if (subscriber == b.subscriber) |
616 |
return true; |
617 |
} |
618 |
} |
619 |
} |
620 |
return false; |
621 |
} |
622 |
|
623 |
/** |
624 |
* Returns an estimate of the number of buffered items (those |
625 |
* produced but not consumed), summed across all current |
626 |
* subscribers. |
627 |
* |
628 |
* @return the estimate |
629 |
*/ |
630 |
public long estimateBuffered() { |
631 |
long sum = 0L; |
632 |
synchronized (this) { |
633 |
BufferedSubscription<T> pred = null, next; |
634 |
for (BufferedSubscription<T> b = clients; b != null; b = next) { |
635 |
next = b.next; |
636 |
if (b.isDisabled()) { |
637 |
if (pred == null) |
638 |
clients = next; |
639 |
else |
640 |
pred.next = next; |
641 |
} |
642 |
else |
643 |
sum += b.estimateBuffered(); |
644 |
} |
645 |
} |
646 |
return sum; |
647 |
} |
648 |
|
649 |
/** |
650 |
* A bounded (ring) buffer with integrated control to start a |
651 |
* consumer task whenever items are available. The buffer |
652 |
* algorithm is similar to one used inside ForkJoinPool, |
653 |
* specialized for the case of at most one concurrent producer and |
654 |
* consumer, and power of two buffer sizes. This allows methods to |
655 |
* operate without locks even while supporting resizing, blocking, |
656 |
* task-triggering, and garbage-free buffers (nulling out elements |
657 |
* when consumed), although supporting these does impose a bit of |
658 |
* overhead compared to plain fixed-size ring buffers. |
659 |
* |
660 |
* The publisher guarantees a single producer via its lock. We |
661 |
* ensure in this class that there is at most one consumer. The |
662 |
* request and cancel methods must be fully thread-safe but are |
663 |
* coded to exploit the most common case in which they are only |
664 |
* called by consumers (usually within onNext). |
665 |
* |
666 |
* This class also serves as its own consumer task, consuming as |
667 |
* many items/signals as possible before terminating, at which |
668 |
* point it is re-executed when needed. (The dual Runnable and |
669 |
* ForkJoinTask declaration saves overhead when executed by |
670 |
* ForkJoinPools, without impacting other kinds of Executors.) |
671 |
* Execution control is managed using the ACTIVE ctl bit. We |
672 |
* ensure that a task is active when consumable items (and |
673 |
* usually, SUBSCRIBE, ERROR or COMPLETE signals) are present and |
674 |
* there is demand (unfulfilled requests). This is complicated on |
675 |
* the creation side by the possibility of exceptions when trying |
676 |
* to execute tasks. These eventually force DISABLED state, but |
677 |
* sometimes not directly. On the task side, termination (clearing |
678 |
* ACTIVE) may race with producers or request() calls, so in some |
679 |
* cases requires a re-check, re-activating if possible. |
680 |
* |
681 |
* The ctl field also manages run state. When DISABLED, no further |
682 |
* updates are possible. Disabling may be preceded by setting |
683 |
* ERROR or COMPLETE (or both -- ERROR has precedence), in which |
684 |
* case the associated Subscriber methods are invoked, possibly |
685 |
* synchronously if there is no active consumer task (including |
686 |
* cases where execute() failed). The cancel() method is supported |
687 |
* by treating as ERROR but suppressing onError signal. |
688 |
* |
689 |
* Support for blocking also exploits the fact that there is only |
690 |
* one possible waiter. ManagedBlocker-compatible control fields |
691 |
* are placed in this class itself rather than in wait-nodes. |
692 |
* Blocking control relies on the "waiter" field. Producers set |
693 |
* the field before trying to block, but must then recheck (via |
694 |
* offer) before parking. Signalling then just unparks and clears |
695 |
* waiter field. If the producer and consumer are both in the same |
696 |
* ForkJoinPool, the producer attempts to help run consumer tasks |
697 |
* that it forked before blocking. |
698 |
* |
699 |
* This class uses @Contended and heuristic field declaration |
700 |
* ordering to reduce memory contention on BufferedSubscription |
701 |
* itself, but it does not currently attempt to avoid memory |
702 |
* contention (especially including card-marks) among buffer |
703 |
* elements, that can significantly slow down some usages. |
704 |
* Addressing this may require allocating substantially more space |
705 |
* than users expect. |
706 |
*/ |
707 |
@SuppressWarnings("serial") |
708 |
@sun.misc.Contended |
709 |
static final class BufferedSubscription<T> extends ForkJoinTask<Void> |
710 |
implements Runnable, Flow.Subscription, ForkJoinPool.ManagedBlocker { |
711 |
// Order-sensitive field declarations |
712 |
long timeout; // > 0 if timed wait |
713 |
volatile long demand; // # unfilled requests |
714 |
final int minCapacity; // initial buffer size |
715 |
int maxCapacity; // reduced on OOME |
716 |
int putStat; // offer result for ManagedBlocker |
717 |
volatile int ctl; // atomic run state flags |
718 |
volatile int head; // next position to take |
719 |
volatile int tail; // next position to put |
720 |
volatile Object[] array; // buffer: null if disabled |
721 |
Flow.Subscriber<? super T> subscriber; // null if disabled |
722 |
Executor executor; // null if disabled |
723 |
volatile Throwable pendingError; // holds until onError issued |
724 |
volatile Thread waiter; // blocked producer thread |
725 |
T putItem; // for offer within ManagedBlocker |
726 |
BufferedSubscription<T> next; // used only by publisher |
727 |
|
728 |
// ctl values |
729 |
static final int ACTIVE = 0x01; // consumer task active |
730 |
static final int DISABLED = 0x02; // final state |
731 |
static final int ERROR = 0x04; // signal onError then disable |
732 |
static final int SUBSCRIBE = 0x08; // signal onSubscribe |
733 |
static final int COMPLETE = 0x10; // signal onComplete when done |
734 |
|
735 |
static final long INTERRUPTED = -1L; // timeout vs interrupt sentinel |
736 |
|
737 |
BufferedSubscription(Flow.Subscriber<? super T> subscriber, |
738 |
Executor executor, int minBufferCapacity, |
739 |
int maxBufferCapacity) { |
740 |
this.subscriber = subscriber; |
741 |
this.executor = executor; |
742 |
this.minCapacity = minBufferCapacity; |
743 |
this.maxCapacity = maxBufferCapacity; |
744 |
} |
745 |
|
746 |
final boolean isDisabled() { |
747 |
return ctl == DISABLED; |
748 |
} |
749 |
|
750 |
final int estimateBuffered() { |
751 |
int n; |
752 |
return (ctl != DISABLED && (n = tail - head) > 0) ? n : 0; |
753 |
} |
754 |
|
755 |
/** |
756 |
* Tries to add item and start consumer task if necessary. |
757 |
* @return -1 if disabled, 0 if dropped, else 1 |
758 |
*/ |
759 |
final int offer(T item) { |
760 |
Object[] a = array; |
761 |
int t = tail, h = head, n, i, stat; |
762 |
if (a != null && (n = a.length) > t - h && (i = t & (n - 1)) >= 0) { |
763 |
a[i] = item; |
764 |
U.putOrderedInt(this, TAIL, t + 1); |
765 |
} |
766 |
else if ((stat = growAndAdd(a, item)) <= 0) |
767 |
return stat; |
768 |
for (int c;;) { // possibly start task |
769 |
Executor e; |
770 |
if (((c = ctl) & ACTIVE) != 0) |
771 |
break; |
772 |
else if (c == DISABLED || (e = executor) == null) |
773 |
return -1; |
774 |
else if (demand == 0L || tail == head) |
775 |
break; |
776 |
else if (U.compareAndSwapInt(this, CTL, c, c | ACTIVE)) { |
777 |
try { |
778 |
e.execute(this); |
779 |
break; |
780 |
} catch (RuntimeException | Error ex) { // back out |
781 |
do {} while ((c = ctl) >= 0 && |
782 |
(c & ACTIVE) != 0 && |
783 |
!U.compareAndSwapInt(this, CTL, c, |
784 |
c & ~ACTIVE)); |
785 |
throw ex; |
786 |
} |
787 |
} |
788 |
} |
789 |
return 1; |
790 |
} |
791 |
|
792 |
/** |
793 |
* Tries to create or expand buffer, then adds item if possible |
794 |
*/ |
795 |
final int growAndAdd(Object[] oldArray, T item) { |
796 |
int oldLen, newLen; |
797 |
if (oldArray != null) |
798 |
newLen = (oldLen = oldArray.length) << 1; |
799 |
else if (ctl >= 0) { |
800 |
oldLen = 0; |
801 |
newLen = minCapacity; |
802 |
} |
803 |
else |
804 |
return -1; // disabled |
805 |
if (oldLen >= maxCapacity || newLen <= 0) |
806 |
return 0; // cannot grow |
807 |
Object[] newArray; |
808 |
try { |
809 |
newArray = new Object[newLen]; |
810 |
} catch (Throwable ex) { // try to cope with OOME |
811 |
if (oldLen > 0) // avoid continuous failure |
812 |
maxCapacity = oldLen; |
813 |
return 0; |
814 |
} |
815 |
array = newArray; |
816 |
int t = tail, oldMask = oldLen - 1, newMask = newLen - 1; |
817 |
if (oldArray != null && oldMask >= 0 && newMask >= oldMask) { |
818 |
for (int j = head; j != t; ++j) { // races with consumer |
819 |
Object x; |
820 |
int i = j & oldMask; |
821 |
if ((x = oldArray[i]) != null && |
822 |
U.compareAndSwapObject(oldArray, |
823 |
(((long)i) << ASHIFT) + ABASE, |
824 |
x, null)) |
825 |
newArray[j & newMask] = x; |
826 |
} |
827 |
} |
828 |
newArray[t & newMask] = item; |
829 |
tail = t + 1; |
830 |
return 1; |
831 |
} |
832 |
|
833 |
/** |
834 |
* Spins/helps/blocks while offer returns 0 |
835 |
*/ |
836 |
final int submit(T item) { |
837 |
int stat; |
838 |
if ((stat = offer(item)) == 0) { |
839 |
Thread thread = Thread.currentThread(); |
840 |
if ((thread instanceof ForkJoinWorkerThread) && |
841 |
((ForkJoinWorkerThread)thread).getPool() == executor) { |
842 |
for (ForkJoinTask<?> t;;) { // try helping |
843 |
if ((t = ForkJoinTask.peekNextLocalTask()) == null || |
844 |
!(t instanceof BufferedSubscription)) |
845 |
break; |
846 |
if (t.tryUnfork()) |
847 |
t.exec(); |
848 |
if ((stat = offer(item)) != 0) |
849 |
break; |
850 |
} |
851 |
} |
852 |
if (stat == 0) { |
853 |
putItem = item; |
854 |
timeout = 0L; |
855 |
try { |
856 |
ForkJoinPool.managedBlock(this); |
857 |
} catch (InterruptedException ie) { |
858 |
timeout = INTERRUPTED; |
859 |
} |
860 |
stat = putStat; |
861 |
if (timeout < 0L) |
862 |
Thread.currentThread().interrupt(); |
863 |
} |
864 |
} |
865 |
return stat; |
866 |
} |
867 |
|
868 |
/** |
869 |
* Timeout version of offer |
870 |
*/ |
871 |
final int offerNanos(T item, long nanos) { |
872 |
int stat; |
873 |
if ((stat = offer(item)) == 0 && nanos > 0L) { |
874 |
Thread thread = Thread.currentThread(); |
875 |
if ((thread instanceof ForkJoinWorkerThread) && |
876 |
((ForkJoinWorkerThread)thread).getPool() == executor) { |
877 |
long deadline = System.nanoTime() + nanos; |
878 |
for (ForkJoinTask<?> t;;) { // similar to above |
879 |
if ((t = ForkJoinTask.peekNextLocalTask()) == null || |
880 |
!(t instanceof BufferedSubscription)) |
881 |
break; |
882 |
if (t.tryUnfork()) |
883 |
t.exec(); |
884 |
if ((stat = offer(item)) != 0 || |
885 |
(nanos = deadline - System.nanoTime()) <= 0L) |
886 |
break; |
887 |
} |
888 |
} |
889 |
if (stat == 0 && (timeout = nanos) > 0L) { |
890 |
putItem = item; |
891 |
try { |
892 |
ForkJoinPool.managedBlock(this); |
893 |
} catch (InterruptedException ie) { |
894 |
timeout = INTERRUPTED; |
895 |
} |
896 |
stat = putStat; |
897 |
if (timeout < 0L) |
898 |
Thread.currentThread().interrupt(); |
899 |
} |
900 |
} |
901 |
return stat; |
902 |
} |
903 |
|
904 |
/** |
905 |
* Nulls out most fields, mainly to avoid garbage retention |
906 |
* until publisher unsubscribes, but also to help cleanly stop |
907 |
* upon error by nulling required components. |
908 |
*/ |
909 |
final void detach() { |
910 |
pendingError = null; |
911 |
subscriber = null; |
912 |
executor = null; |
913 |
array = null; |
914 |
Thread w = waiter; |
915 |
if (w != null) { |
916 |
waiter = null; |
917 |
LockSupport.unpark(w); // force wakeup |
918 |
} |
919 |
} |
920 |
|
921 |
/** |
922 |
* Issues error signal, asynchronously if a task is running, |
923 |
* else synchronously |
924 |
*/ |
925 |
final void onError(Throwable ex) { |
926 |
for (int c;;) { |
927 |
if ((c = ctl) == DISABLED) |
928 |
break; |
929 |
else if ((c & ACTIVE) != 0) { |
930 |
pendingError = ex; |
931 |
if (U.compareAndSwapInt(this, CTL, c, c | ERROR)) |
932 |
break; // cause consumer task to exit |
933 |
} |
934 |
else if (U.compareAndSwapInt(this, CTL, c, DISABLED)) { |
935 |
Flow.Subscriber<? super T> s = subscriber; |
936 |
if (s != null && ex != null) { |
937 |
try { |
938 |
s.onError(ex); |
939 |
} catch (Throwable ignore) { |
940 |
} |
941 |
} |
942 |
detach(); |
943 |
break; |
944 |
} |
945 |
} |
946 |
} |
947 |
|
948 |
/** |
949 |
* Tries to start consumer task upon a signal or request; |
950 |
* disables on failure. |
951 |
*/ |
952 |
final void startOrDisable() { |
953 |
Executor e; // skip if already disabled |
954 |
if ((e = executor) != null) { |
955 |
try { |
956 |
e.execute(this); |
957 |
} catch (Throwable ex) { // back out and force signal |
958 |
for (int c;;) { |
959 |
if ((c = ctl) == DISABLED || (c & ACTIVE) == 0) |
960 |
break; |
961 |
if (U.compareAndSwapInt(this, CTL, c, c & ~ACTIVE)) { |
962 |
onError(ex); |
963 |
break; |
964 |
} |
965 |
} |
966 |
} |
967 |
} |
968 |
} |
969 |
|
970 |
final void onComplete() { |
971 |
for (int c;;) { |
972 |
if ((c = ctl) == DISABLED) |
973 |
break; |
974 |
if (U.compareAndSwapInt(this, CTL, c, c | (ACTIVE | COMPLETE))) { |
975 |
if ((c & ACTIVE) == 0) |
976 |
startOrDisable(); |
977 |
break; |
978 |
} |
979 |
} |
980 |
} |
981 |
|
982 |
final void onSubscribe() { |
983 |
for (int c;;) { |
984 |
if ((c = ctl) == DISABLED) |
985 |
break; |
986 |
if (U.compareAndSwapInt(this, CTL, c, c | (ACTIVE | SUBSCRIBE))) { |
987 |
if ((c & ACTIVE) == 0) |
988 |
startOrDisable(); |
989 |
break; |
990 |
} |
991 |
} |
992 |
} |
993 |
|
994 |
/** |
995 |
* Causes consumer task to exit if active (without reporting |
996 |
* onError unless there is already a pending error), and |
997 |
* disables. |
998 |
*/ |
999 |
public void cancel() { |
1000 |
for (int c;;) { |
1001 |
if ((c = ctl) == DISABLED) |
1002 |
break; |
1003 |
else if ((c & ACTIVE) != 0) { |
1004 |
if (U.compareAndSwapInt(this, CTL, c, c | ERROR)) |
1005 |
break; |
1006 |
} |
1007 |
else if (U.compareAndSwapInt(this, CTL, c, DISABLED)) { |
1008 |
detach(); |
1009 |
break; |
1010 |
} |
1011 |
} |
1012 |
} |
1013 |
|
1014 |
/** |
1015 |
* Adds to demand and possibly starts task. |
1016 |
*/ |
1017 |
public void request(long n) { |
1018 |
if (n > 0L) { |
1019 |
for (;;) { |
1020 |
long prev = demand, d; |
1021 |
if ((d = prev + n) < prev) // saturate |
1022 |
d = Long.MAX_VALUE; |
1023 |
if (U.compareAndSwapLong(this, DEMAND, prev, d)) { |
1024 |
for (int c, h;;) { |
1025 |
if (((c = ctl) & (ACTIVE | DISABLED)) != 0 || |
1026 |
demand == 0L) |
1027 |
break; |
1028 |
if ((h = head) != tail) { |
1029 |
if (U.compareAndSwapInt(this, CTL, c, |
1030 |
c | ACTIVE)) { |
1031 |
startOrDisable(); |
1032 |
break; |
1033 |
} |
1034 |
} |
1035 |
else if (head == h && tail == h) |
1036 |
break; |
1037 |
} |
1038 |
break; |
1039 |
} |
1040 |
} |
1041 |
} |
1042 |
else if (n < 0L) |
1043 |
onError(new IllegalArgumentException( |
1044 |
"negative subscription request")); |
1045 |
} |
1046 |
|
1047 |
public final boolean isReleasable() { // for ManagedBlocker |
1048 |
T item = putItem; |
1049 |
if (item != null) { |
1050 |
if ((putStat = offer(item)) == 0) |
1051 |
return false; |
1052 |
putItem = null; |
1053 |
} |
1054 |
return true; |
1055 |
} |
1056 |
|
1057 |
public final boolean block() { // for ManagedBlocker |
1058 |
T item = putItem; |
1059 |
if (item != null) { |
1060 |
putItem = null; |
1061 |
long nanos = timeout; |
1062 |
long deadline = (nanos > 0L) ? System.nanoTime() + nanos : 0L; |
1063 |
while ((putStat = offer(item)) == 0) { |
1064 |
if (Thread.interrupted()) { |
1065 |
timeout = INTERRUPTED; |
1066 |
if (nanos > 0L) |
1067 |
break; |
1068 |
} |
1069 |
else if (nanos > 0L && |
1070 |
(nanos = deadline - System.nanoTime()) <= 0L) |
1071 |
break; |
1072 |
else if (waiter == null) |
1073 |
waiter = Thread.currentThread(); |
1074 |
else { |
1075 |
if (nanos > 0L) |
1076 |
LockSupport.parkNanos(this, nanos); |
1077 |
else |
1078 |
LockSupport.park(this); |
1079 |
waiter = null; |
1080 |
} |
1081 |
} |
1082 |
} |
1083 |
waiter = null; |
1084 |
return true; |
1085 |
} |
1086 |
|
1087 |
/** |
1088 |
* Consumer task loop; supports resubmission when used as |
1089 |
* ForkJoinTask. |
1090 |
*/ |
1091 |
public final boolean exec() { |
1092 |
Flow.Subscriber<? super T> s; |
1093 |
if ((s = subscriber) != null) { // else disabled |
1094 |
for (;;) { |
1095 |
long d = demand; // read volatile fields in acceptable order |
1096 |
int c = ctl; |
1097 |
int h = head; |
1098 |
int t = tail; |
1099 |
Object[] a = array; |
1100 |
int i, n; Object x; Thread w; |
1101 |
if ((c & (ERROR | SUBSCRIBE | DISABLED)) != 0) { |
1102 |
if ((c & ERROR) != 0) { |
1103 |
Throwable ex = pendingError; |
1104 |
ctl = DISABLED; // no need for CAS |
1105 |
if (ex != null) { |
1106 |
try { |
1107 |
s.onError(ex); |
1108 |
} catch (Throwable ignore) { |
1109 |
} |
1110 |
} |
1111 |
} |
1112 |
else if ((c & SUBSCRIBE) != 0) { |
1113 |
if (U.compareAndSwapInt(this, CTL, c, |
1114 |
c & ~SUBSCRIBE)) { |
1115 |
try { |
1116 |
s.onSubscribe(this); |
1117 |
} catch (Throwable ex) { |
1118 |
ctl = DISABLED; |
1119 |
} |
1120 |
} |
1121 |
} |
1122 |
else { |
1123 |
detach(); |
1124 |
break; |
1125 |
} |
1126 |
} |
1127 |
else if (h == t) { // empty |
1128 |
if (h == tail && |
1129 |
U.compareAndSwapInt(this, CTL, c, c &= ~ACTIVE)) { |
1130 |
if (h != tail || c != (c = ctl)) { // recheck |
1131 |
if ((c & (ACTIVE | DISABLED)) != 0 || |
1132 |
!U.compareAndSwapInt(this, CTL, c, |
1133 |
c | ACTIVE)) |
1134 |
break; |
1135 |
} |
1136 |
else if ((c & COMPLETE) != 0) { |
1137 |
ctl = DISABLED; |
1138 |
try { |
1139 |
s.onComplete(); |
1140 |
} catch (Throwable ignore) { |
1141 |
} |
1142 |
} |
1143 |
else |
1144 |
break; |
1145 |
} |
1146 |
} |
1147 |
else if (a == null || (n = a.length) == 0 || |
1148 |
(x = a[i = h & (n - 1)]) == null) |
1149 |
; // stale; retry |
1150 |
else if (d == 0L) { // can't take |
1151 |
if (demand == 0L && |
1152 |
U.compareAndSwapInt(this, CTL, c, c &= ~ACTIVE) && |
1153 |
((demand == 0L && c == (c = ctl)) || // recheck |
1154 |
(c & (ACTIVE | DISABLED)) != 0 || |
1155 |
!U.compareAndSwapInt(this, CTL, c, c | ACTIVE))) |
1156 |
break; |
1157 |
} |
1158 |
else if (U.compareAndSwapObject( |
1159 |
a, (((long)i) << ASHIFT) + ABASE, x, null)) { |
1160 |
U.putOrderedInt(this, HEAD, h + 1); |
1161 |
while (!U.compareAndSwapLong(this, DEMAND, d, d - 1L)) |
1162 |
d = demand; // almost never fails |
1163 |
if ((w = waiter) != null) { |
1164 |
waiter = null; |
1165 |
LockSupport.unpark(w); // release producer |
1166 |
} |
1167 |
try { |
1168 |
@SuppressWarnings("unchecked") T y = (T) x; |
1169 |
s.onNext(y); |
1170 |
} catch (Throwable ex) { // disable on throw |
1171 |
ctl = DISABLED; |
1172 |
} |
1173 |
} |
1174 |
} |
1175 |
} |
1176 |
return false; // resubmittable; never joined |
1177 |
} |
1178 |
|
1179 |
// Runnable and FJ support |
1180 |
public final void run() { exec(); } |
1181 |
public final Void getRawResult() { return null; } |
1182 |
public final void setRawResult(Void v) {} |
1183 |
|
1184 |
// Unsafe mechanics |
1185 |
private static final sun.misc.Unsafe U = sun.misc.Unsafe.getUnsafe(); |
1186 |
private static final long CTL; |
1187 |
private static final long TAIL; |
1188 |
private static final long HEAD; |
1189 |
private static final long DEMAND; |
1190 |
private static final int ABASE; |
1191 |
private static final int ASHIFT; |
1192 |
|
1193 |
static { |
1194 |
try { |
1195 |
CTL = U.objectFieldOffset |
1196 |
(BufferedSubscription.class.getDeclaredField("ctl")); |
1197 |
TAIL = U.objectFieldOffset |
1198 |
(BufferedSubscription.class.getDeclaredField("tail")); |
1199 |
HEAD = U.objectFieldOffset |
1200 |
(BufferedSubscription.class.getDeclaredField("head")); |
1201 |
DEMAND = U.objectFieldOffset |
1202 |
(BufferedSubscription.class.getDeclaredField("demand")); |
1203 |
|
1204 |
ABASE = U.arrayBaseOffset(Object[].class); |
1205 |
int scale = U.arrayIndexScale(Object[].class); |
1206 |
if ((scale & (scale - 1)) != 0) |
1207 |
throw new Error("data type scale not a power of two"); |
1208 |
ASHIFT = 31 - Integer.numberOfLeadingZeros(scale); |
1209 |
} catch (ReflectiveOperationException e) { |
1210 |
throw new Error(e); |
1211 |
} |
1212 |
} |
1213 |
} |
1214 |
} |