Class SubmissionPublisher<T>
- Type Parameters:
- T- the published item type
- All Implemented Interfaces:
- AutoCloseable,- Flow.Publisher<T>
Flow.Publisher that asynchronously issues submitted
 (non-null) items to current subscribers until it is closed.  Each
 current subscriber receives newly submitted items in the same order
 unless drops or exceptions are encountered.  Using a
 SubmissionPublisher allows item generators to act as compliant  reactive-streams
 Publishers relying on drop handling and/or blocking for flow
 control.
 A SubmissionPublisher uses the Executor supplied in its
 constructor for delivery to subscribers. The best choice of
 Executor depends on expected usage. If the generator(s) of
 submitted items run in separate threads, and the number of
 subscribers can be estimated, consider using a Executors.newFixedThreadPool(int). Otherwise consider using the
 default, normally the ForkJoinPool.commonPool().
 
Buffering allows producers and consumers to transiently operate
 at different rates.  Each subscriber uses an independent buffer.
 Buffers are created upon first use and expanded as needed up to the
 given maximum. (The enforced capacity may be rounded up to the
 nearest power of two and/or bounded by the largest value supported
 by this implementation.)  Invocations of request do not directly result in
 buffer expansion, but risk saturation if unfilled requests exceed
 the maximum capacity.  The default value of Flow.defaultBufferSize() may provide a useful starting point for
 choosing a capacity based on expected rates, resources, and usages.
 
A single SubmissionPublisher may be shared among multiple sources. Actions in a source thread prior to publishing an item or issuing a signal happen-before actions subsequent to the corresponding access by each subscriber. But reported estimates of lag and demand are designed for use in monitoring, not for synchronization control, and may reflect stale or inaccurate views of progress.
Publication methods support different policies about what to do
 when buffers are saturated. Method submit
 blocks until resources are available. This is simplest, but least
 responsive.  The offer methods may drop items (either
 immediately or with bounded timeout), but provide an opportunity to
 interpose a handler and then retry.
 
If any Subscriber method throws an exception, its subscription
 is cancelled.  If a handler is supplied as a constructor argument,
 it is invoked before cancellation upon an exception in method
 onNext, but exceptions in methods
 onSubscribe,
 onError and
 onComplete are not recorded or
 handled before cancellation.  If the supplied Executor throws
 RejectedExecutionException (or any other RuntimeException
 or Error) when attempting to execute a task, or a drop handler
 throws an exception when processing a dropped item, then the
 exception is rethrown. In these cases, not all subscribers will
 have been issued the published item. It is usually good practice to
 closeExceptionally in these cases.
 
Method consume(Consumer) simplifies support for a
 common case in which the only action of a subscriber is to request
 and process all items using a supplied function.
 
This class may also serve as a convenient base for subclasses that generate items, and use the methods in this class to publish them. For example here is a class that periodically publishes the items generated from a supplier. (In practice you might add methods to independently start and stop generation, to share Executors among publishers, and so on, or use a SubmissionPublisher as a component rather than a superclass.)
 
 class PeriodicPublisher<T> extends SubmissionPublisher<T> {
   final ScheduledFuture<?> periodicTask;
   final ScheduledExecutorService scheduler;
   PeriodicPublisher(Executor executor, int maxBufferCapacity,
                     Supplier<? extends T> supplier,
                     long period, TimeUnit unit) {
     super(executor, maxBufferCapacity);
     scheduler = new ScheduledThreadPoolExecutor(1);
     periodicTask = scheduler.scheduleAtFixedRate(
       () -> submit(supplier.get()), 0, period, unit);
   }
   public void close() {
     periodicTask.cancel(false);
     scheduler.shutdown();
     super.close();
   }
 }
 Here is an example of a Flow.Processor implementation.
 It uses single-step requests to its publisher for simplicity of
 illustration. A more adaptive version could monitor flow using the
 lag estimate returned from submit, along with other utility
 methods.
 
 
 class TransformProcessor<S,T> extends SubmissionPublisher<T>
   implements Flow.Processor<S,T> {
   final Function<? super S, ? extends T> function;
   Flow.Subscription subscription;
   TransformProcessor(Executor executor, int maxBufferCapacity,
                      Function<? super S, ? extends T> function) {
     super(executor, maxBufferCapacity);
     this.function = function;
   }
   public void onSubscribe(Flow.Subscription subscription) {
     (this.subscription = subscription).request(1);
   }
   public void onNext(S item) {
     subscription.request(1);
     submit(function.apply(item));
   }
   public void onError(Throwable ex) { closeExceptionally(ex); }
   public void onComplete() { close(); }
 }- Since:
- 9
- 
Constructor SummaryConstructorsConstructorDescriptionCreates a new SubmissionPublisher using theForkJoinPool.commonPool()for async delivery to subscribers (unless it does not support a parallelism level of at least two, in which case, a new Thread is created to run each task), with maximum buffer capacity ofFlow.defaultBufferSize(), and no handler for Subscriber exceptions in methodonNext.SubmissionPublisher(Executor executor, int maxBufferCapacity) Creates a new SubmissionPublisher using the given Executor for async delivery to subscribers, with the given maximum buffer size for each subscriber, and no handler for Subscriber exceptions in methodonNext.SubmissionPublisher(Executor executor, int maxBufferCapacity, BiConsumer<? super Flow.Subscriber<? super T>, ? super Throwable> handler) Creates a new SubmissionPublisher using the given Executor for async delivery to subscribers, with the given maximum buffer size for each subscriber, and, if non-null, the given handler invoked when any Subscriber throws an exception in methodonNext.
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Method SummaryModifier and TypeMethodDescriptionvoidclose()Unless already closed, issuesonCompletesignals to current subscribers, and disallows subsequent attempts to publish.voidcloseExceptionally(Throwable error) Unless already closed, issuesonErrorsignals to current subscribers with the given error, and disallows subsequent attempts to publish.Processes all published items using the given Consumer function.intReturns an estimate of the maximum number of items produced but not yet consumed among all current subscribers.longReturns an estimate of the minimum number of items requested (viarequest) but not yet produced, among all current subscribers.Returns the exception associated withcloseExceptionally, or null if not closed or if closed normally.Returns the Executor used for asynchronous delivery.intReturns the maximum per-subscriber buffer capacity.intReturns the number of current subscribers.List<Flow.Subscriber<? super T>> Returns a list of current subscribers for monitoring and tracking purposes, not for invokingFlow.Subscribermethods on the subscribers.booleanReturns true if this publisher has any subscribers.booleanisClosed()Returns true if this publisher is not accepting submissions.booleanisSubscribed(Flow.Subscriber<? super T> subscriber) Returns true if the given Subscriber is currently subscribed.intoffer(T item, long timeout, TimeUnit unit, BiPredicate<Flow.Subscriber<? super T>, ? super T> onDrop) Publishes the given item, if possible, to each current subscriber by asynchronously invoking itsonNextmethod, blocking while resources for any subscription are unavailable, up to the specified timeout or until the caller thread is interrupted, at which point the given handler (if non-null) is invoked, and if it returns true, retried once.intoffer(T item, BiPredicate<Flow.Subscriber<? super T>, ? super T> onDrop) Publishes the given item, if possible, to each current subscriber by asynchronously invoking itsonNextmethod.intPublishes the given item to each current subscriber by asynchronously invoking itsonNextmethod, blocking uninterruptibly while resources for any subscriber are unavailable.voidsubscribe(Flow.Subscriber<? super T> subscriber) Adds the given Subscriber unless already subscribed.
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Constructor Details- 
SubmissionPublisherpublic SubmissionPublisher(Executor executor, int maxBufferCapacity, BiConsumer<? super Flow.Subscriber<? super T>, ? super Throwable> handler) Creates a new SubmissionPublisher using the given Executor for async delivery to subscribers, with the given maximum buffer size for each subscriber, and, if non-null, the given handler invoked when any Subscriber throws an exception in methodonNext.- Parameters:
- executor- the executor to use for async delivery, supporting creation of at least one independent thread
- maxBufferCapacity- the maximum capacity for each subscriber's buffer (the enforced capacity may be rounded up to the nearest power of two and/or bounded by the largest value supported by this implementation; method- getMaxBufferCapacity()returns the actual value)
- handler- if non-null, procedure to invoke upon exception thrown in method- onNext
- Throws:
- NullPointerException- if executor is null
- IllegalArgumentException- if maxBufferCapacity not positive
 
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SubmissionPublisherCreates a new SubmissionPublisher using the given Executor for async delivery to subscribers, with the given maximum buffer size for each subscriber, and no handler for Subscriber exceptions in methodonNext.- Parameters:
- executor- the executor to use for async delivery, supporting creation of at least one independent thread
- maxBufferCapacity- the maximum capacity for each subscriber's buffer (the enforced capacity may be rounded up to the nearest power of two and/or bounded by the largest value supported by this implementation; method- getMaxBufferCapacity()returns the actual value)
- Throws:
- NullPointerException- if executor is null
- IllegalArgumentException- if maxBufferCapacity not positive
 
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SubmissionPublisherpublic SubmissionPublisher()Creates a new SubmissionPublisher using theForkJoinPool.commonPool()for async delivery to subscribers (unless it does not support a parallelism level of at least two, in which case, a new Thread is created to run each task), with maximum buffer capacity ofFlow.defaultBufferSize(), and no handler for Subscriber exceptions in methodonNext.
 
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Method Details- 
subscribeAdds the given Subscriber unless already subscribed. If already subscribed, the Subscriber'sonErrormethod is invoked on the existing subscription with anIllegalStateException. Otherwise, upon success, the Subscriber'sonSubscribemethod is invoked asynchronously with a newFlow.Subscription. IfonSubscribethrows an exception, the subscription is cancelled. Otherwise, if this SubmissionPublisher was closed exceptionally, then the subscriber'sonErrormethod is invoked with the corresponding exception, or if closed without exception, the subscriber'sonCompletemethod is invoked. Subscribers may enable receiving items by invoking therequestmethod of the new Subscription, and may unsubscribe by invoking itscancelmethod.- Specified by:
- subscribein interface- Flow.Publisher<T>
- Parameters:
- subscriber- the subscriber
- Throws:
- NullPointerException- if subscriber is null
 
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submitPublishes the given item to each current subscriber by asynchronously invoking itsonNextmethod, blocking uninterruptibly while resources for any subscriber are unavailable. This method returns an estimate of the maximum lag (number of items submitted but not yet consumed) among all current subscribers. This value is at least one (accounting for this submitted item) if there are any subscribers, else zero.If the Executor for this publisher throws a RejectedExecutionException (or any other RuntimeException or Error) when attempting to asynchronously notify subscribers, then this exception is rethrown, in which case not all subscribers will have been issued this item. - Parameters:
- item- the (non-null) item to publish
- Returns:
- the estimated maximum lag among subscribers
- Throws:
- IllegalStateException- if closed
- NullPointerException- if item is null
- RejectedExecutionException- if thrown by Executor
 
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offerPublishes the given item, if possible, to each current subscriber by asynchronously invoking itsonNextmethod. The item may be dropped by one or more subscribers if resource limits are exceeded, in which case the given handler (if non-null) is invoked, and if it returns true, retried once. Other calls to methods in this class by other threads are blocked while the handler is invoked. Unless recovery is assured, options are usually limited to logging the error and/or issuing anonErrorsignal to the subscriber.This method returns a status indicator: If negative, it represents the (negative) number of drops (failed attempts to issue the item to a subscriber). Otherwise it is an estimate of the maximum lag (number of items submitted but not yet consumed) among all current subscribers. This value is at least one (accounting for this submitted item) if there are any subscribers, else zero. If the Executor for this publisher throws a RejectedExecutionException (or any other RuntimeException or Error) when attempting to asynchronously notify subscribers, or the drop handler throws an exception when processing a dropped item, then this exception is rethrown. - Parameters:
- item- the (non-null) item to publish
- onDrop- if non-null, the handler invoked upon a drop to a subscriber, with arguments of the subscriber and item; if it returns true, an offer is re-attempted (once)
- Returns:
- if negative, the (negative) number of drops; otherwise an estimate of maximum lag
- Throws:
- IllegalStateException- if closed
- NullPointerException- if item is null
- RejectedExecutionException- if thrown by Executor
 
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offerpublic int offer(T item, long timeout, TimeUnit unit, BiPredicate<Flow.Subscriber<? super T>, ? super T> onDrop) Publishes the given item, if possible, to each current subscriber by asynchronously invoking itsonNextmethod, blocking while resources for any subscription are unavailable, up to the specified timeout or until the caller thread is interrupted, at which point the given handler (if non-null) is invoked, and if it returns true, retried once. (The drop handler may distinguish timeouts from interrupts by checking whether the current thread is interrupted.) Other calls to methods in this class by other threads are blocked while the handler is invoked. Unless recovery is assured, options are usually limited to logging the error and/or issuing anonErrorsignal to the subscriber.This method returns a status indicator: If negative, it represents the (negative) number of drops (failed attempts to issue the item to a subscriber). Otherwise it is an estimate of the maximum lag (number of items submitted but not yet consumed) among all current subscribers. This value is at least one (accounting for this submitted item) if there are any subscribers, else zero. If the Executor for this publisher throws a RejectedExecutionException (or any other RuntimeException or Error) when attempting to asynchronously notify subscribers, or the drop handler throws an exception when processing a dropped item, then this exception is rethrown. - Parameters:
- item- the (non-null) item to publish
- timeout- how long to wait for resources for any subscriber before giving up, in units of- unit
- unit- a- TimeUnitdetermining how to interpret the- timeoutparameter
- onDrop- if non-null, the handler invoked upon a drop to a subscriber, with arguments of the subscriber and item; if it returns true, an offer is re-attempted (once)
- Returns:
- if negative, the (negative) number of drops; otherwise an estimate of maximum lag
- Throws:
- IllegalStateException- if closed
- NullPointerException- if item is null
- RejectedExecutionException- if thrown by Executor
 
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closepublic void close()Unless already closed, issuesonCompletesignals to current subscribers, and disallows subsequent attempts to publish. Upon return, this method does NOT guarantee that all subscribers have yet completed.- Specified by:
- closein interface- AutoCloseable
 
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closeExceptionallyUnless already closed, issuesonErrorsignals to current subscribers with the given error, and disallows subsequent attempts to publish. Future subscribers also receive the given error. Upon return, this method does NOT guarantee that all subscribers have yet completed.- Parameters:
- error- the- onErrorargument sent to subscribers
- Throws:
- NullPointerException- if error is null
 
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isClosedpublic boolean isClosed()Returns true if this publisher is not accepting submissions.- Returns:
- true if closed
 
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getClosedExceptionReturns the exception associated withcloseExceptionally, or null if not closed or if closed normally.- Returns:
- the exception, or null if none
 
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hasSubscriberspublic boolean hasSubscribers()Returns true if this publisher has any subscribers.- Returns:
- true if this publisher has any subscribers
 
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getNumberOfSubscriberspublic int getNumberOfSubscribers()Returns the number of current subscribers.- Returns:
- the number of current subscribers
 
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getExecutorReturns the Executor used for asynchronous delivery.- Returns:
- the Executor used for asynchronous delivery
 
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getMaxBufferCapacitypublic int getMaxBufferCapacity()Returns the maximum per-subscriber buffer capacity.- Returns:
- the maximum per-subscriber buffer capacity
 
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getSubscribersReturns a list of current subscribers for monitoring and tracking purposes, not for invokingFlow.Subscribermethods on the subscribers.- Returns:
- list of current subscribers
 
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isSubscribedReturns true if the given Subscriber is currently subscribed.- Parameters:
- subscriber- the subscriber
- Returns:
- true if currently subscribed
- Throws:
- NullPointerException- if subscriber is null
 
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estimateMinimumDemandpublic long estimateMinimumDemand()Returns an estimate of the minimum number of items requested (viarequest) but not yet produced, among all current subscribers.- Returns:
- the estimate, or zero if no subscribers
 
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estimateMaximumLagpublic int estimateMaximumLag()Returns an estimate of the maximum number of items produced but not yet consumed among all current subscribers.- Returns:
- the estimate
 
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consumeProcesses all published items using the given Consumer function. Returns a CompletableFuture that is completed normally when this publisher signalsonComplete, or completed exceptionally upon any error, or an exception is thrown by the Consumer, or the returned CompletableFuture is cancelled, in which case no further items are processed.- Parameters:
- consumer- the function applied to each onNext item
- Returns:
- a CompletableFuture that is completed normally when the publisher signals onComplete, and exceptionally upon any error or cancellation
- Throws:
- NullPointerException- if consumer is null
 
 
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