T
- the published item typepublic interface SubmittableFlowPublisher<T> extends Flow.Publisher<T>, AutoCloseable
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
SubmittableFlowPublisher allows item generators to act as compliant reactive-streams
Publishers relying on drop handling and/or blocking for flow
control.
An implementation of SubmittableFlowPublisher 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.
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.
Modifier and Type | Method and Description |
---|---|
void |
close()
Unless already closed, issues
onComplete signals to current
subscribers, and disallows subsequent attempts to publish. |
void |
closeExceptionally(Throwable error)
Unless already closed, issues
onError signals to current
subscribers with the given error, and disallows subsequent
attempts to publish. |
CompletableFuture<Void> |
consume(Consumer<? super T> consumer)
Processes all published items using the given Consumer function.
|
int |
estimateMaximumLag()
Returns an estimate of the maximum number of items produced but
not yet consumed among all current subscribers.
|
long |
estimateMinimumDemand()
Returns an estimate of the minimum number of items requested
(via
request ) but not
yet produced, among all current subscribers. |
Throwable |
getClosedException()
Returns the exception associated with
closeExceptionally , or null if
not closed or if closed normally. |
int |
getMaxBufferCapacity()
Returns the maximum per-subscriber buffer capacity.
|
int |
offer(T item,
BiPredicate<Flow.Subscriber<? super T>,? super T> onDrop)
Publishes the given item, if possible, to each current subscriber
by asynchronously invoking its
onNext method. |
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 its
onNext method, 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. |
int |
submit(T item)
Publishes the given item to each current subscriber by
asynchronously invoking its
onNext method, blocking uninterruptibly while resources for any
subscriber are unavailable. |
void |
subscribe(Flow.Subscriber<? super T> subscriber)
Adds the given Subscriber unless already subscribed.
|
CompletableFuture<Void> consume(Consumer<? super T> consumer)
onComplete
, 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.consumer
- the function applied to each onNext itemNullPointerException
- if consumer is nullvoid close()
onComplete
signals to current
subscribers, and disallows subsequent attempts to publish.
Upon return, this method does NOT guarantee that all
subscribers have yet completed.close
in interface AutoCloseable
void closeExceptionally(Throwable error)
onError
signals 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.error
- the onError
argument sent to subscribersNullPointerException
- if error is nulllong estimateMinimumDemand()
request
) but not
yet produced, among all current subscribers.int estimateMaximumLag()
Throwable getClosedException()
closeExceptionally
, or null if
not closed or if closed normally.int getMaxBufferCapacity()
int offer(T item, long timeout, TimeUnit unit, BiPredicate<Flow.Subscriber<? super T>,? super T> onDrop)
onNext
method, 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 an onError
signal 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.
item
- the (non-null) item to publishtimeout
- how long to wait for resources for any subscriber
before giving up, in units of unit
unit
- a TimeUnit
determining how to interpret the
timeout
parameteronDrop
- 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)IllegalStateException
- if closedNullPointerException
- if item is nullRejectedExecutionException
- if thrown by Executorint offer(T item, BiPredicate<Flow.Subscriber<? super T>,? super T> onDrop)
onNext
method. 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 an onError
signal 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.
item
- the (non-null) item to publishonDrop
- 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)IllegalStateException
- if closedNullPointerException
- if item is nullRejectedExecutionException
- if thrown by Executorint submit(T item)
onNext
method, 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.
item
- the (non-null) item to publishIllegalStateException
- if closedNullPointerException
- if item is nullRejectedExecutionException
- if thrown by Executorvoid subscribe(Flow.Subscriber<? super T> subscriber)
onError
method is invoked on
the existing subscription with an IllegalStateException
.
Otherwise, upon success, the Subscriber's onSubscribe
method is invoked
asynchronously with a new Flow.Subscription
. If onSubscribe
throws an exception, the
subscription is cancelled. Otherwise, if this SubmittableFlowPublisher
was closed exceptionally, then the subscriber's onError
method is invoked with the
corresponding exception, or if closed without exception, the
subscriber's onComplete
method is invoked. Subscribers may enable receiving items by
invoking the request
method of the new Subscription, and may unsubscribe by invoking
its cancel
method.subscribe
in interface Flow.Publisher<T>
subscriber
- the subscriberNullPointerException
- if subscriber is nullCopyright © 2007-2024, Oracle and/or its affiliates. All Rights Reserved. Use is subject to license terms.