SchedulerWhen.java
/*
* Copyright (c) 2016-present, RxJava Contributors.
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
* compliance with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software distributed under the License is
* distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
* the License for the specific language governing permissions and limitations under the License.
*/
package io.reactivex.rxjava3.internal.schedulers;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.*;
import io.reactivex.rxjava3.annotations.NonNull;
import io.reactivex.rxjava3.core.*;
import io.reactivex.rxjava3.disposables.*;
import io.reactivex.rxjava3.functions.Function;
import io.reactivex.rxjava3.internal.util.ExceptionHelper;
import io.reactivex.rxjava3.processors.*;
/**
* Allows the use of operators for controlling the timing around when actions
* scheduled on workers are actually done. This makes it possible to layer
* additional behavior on this {@link Scheduler}. The only parameter is a
* function that flattens an {@link Observable} of {@link Observable} of
* {@link Completable}s into just one {@link Completable}. There must be a chain
* of operators connecting the returned value to the source {@link Observable}
* otherwise any work scheduled on the returned {@link Scheduler} will not be
* executed.
* <p>
* When {@link Scheduler#createWorker()} is invoked a {@link Observable} of
* {@link Completable}s is onNext'd to the combinator to be flattened. If the
* inner {@link Observable} is not immediately subscribed to an calls to
* {@link Worker#schedule} are buffered. Once the {@link Observable} is
* subscribed to actions are then onNext'd as {@link Completable}s.
* <p>
* Finally the actions scheduled on the parent {@link Scheduler} when the inner
* most {@link Completable}s are subscribed to.
* <p>
* When the {@link io.reactivex.rxjava3.core.Scheduler.Worker Worker} is unsubscribed the {@link Completable} emits an
* onComplete and triggers any behavior in the flattening operator. The
* {@link Observable} and all {@link Completable}s give to the flattening
* function never onError.
* <p>
* Limit the amount concurrency two at a time without creating a new fix size
* thread pool:
*
* <pre>
* {@code
* Scheduler limitScheduler = Schedulers.computation().when(workers -> {
* // use merge max concurrent to limit the number of concurrent
* // callbacks two at a time
* return Completable.merge(Observable.merge(workers), 2);
* });
* }
* </pre>
* <p>
* This is a slightly different way to limit the concurrency but it has some
* interesting benefits and drawbacks to the method above. It works by limited
* the number of concurrent {@link io.reactivex.rxjava3.core.Scheduler.Worker Worker}s rather than individual actions.
* Generally each {@link Observable} uses its own {@link io.reactivex.rxjava3.core.Scheduler.Worker Worker}. This means
* that this will essentially limit the number of concurrent subscribes. The
* danger comes from using operators like
* {@link Flowable#zip(org.reactivestreams.Publisher, org.reactivestreams.Publisher, io.reactivex.rxjava3.functions.BiFunction)} where
* subscribing to the first {@link Observable} could deadlock the subscription
* to the second.
*
* <pre>
* {@code
* Scheduler limitScheduler = Schedulers.computation().when(workers -> {
* // use merge max concurrent to limit the number of concurrent
* // Observables two at a time
* return Completable.merge(Observable.merge(workers, 2));
* });
* }
* </pre>
*
* Slowing down the rate to no more than 1 a second. This suffers from the
* same problem as the one above I could find an {@link Observable} operator
* that limits the rate without dropping the values (aka leaky bucket
* algorithm).
*
* <pre>
* {@code
* Scheduler slowScheduler = Schedulers.computation().when(workers -> {
* // use concatenate to make each worker happen one at a time.
* return Completable.concat(workers.map(actions -> {
* // delay the starting of the next worker by 1 second.
* return Completable.merge(actions.delaySubscription(1, TimeUnit.SECONDS));
* }));
* });
* }
* </pre>
* <p>History 2.0.1 - experimental
* @since 2.1
*/
public class SchedulerWhen extends Scheduler implements Disposable {
private final Scheduler actualScheduler;
private final FlowableProcessor<Flowable<Completable>> workerProcessor;
private Disposable disposable;
public SchedulerWhen(Function<Flowable<Flowable<Completable>>, Completable> combine, Scheduler actualScheduler) {
this.actualScheduler = actualScheduler;
// workers are converted into completables and put in this queue.
this.workerProcessor = UnicastProcessor.<Flowable<Completable>>create().toSerialized();
// send it to a custom combinator to pick the order and rate at which
// workers are processed.
try {
disposable = combine.apply(workerProcessor).subscribe();
} catch (Throwable e) {
throw ExceptionHelper.wrapOrThrow(e);
}
}
@Override
public void dispose() {
disposable.dispose();
}
@Override
public boolean isDisposed() {
return disposable.isDisposed();
}
@NonNull
@Override
public Worker createWorker() {
final Worker actualWorker = actualScheduler.createWorker();
// a queue for the actions submitted while worker is waiting to get to
// the subscribe to off the workerQueue.
final FlowableProcessor<ScheduledAction> actionProcessor = UnicastProcessor.<ScheduledAction>create().toSerialized();
// convert the work of scheduling all the actions into a completable
Flowable<Completable> actions = actionProcessor.map(new CreateWorkerFunction(actualWorker));
// a worker that queues the action to the actionQueue subject.
Worker worker = new QueueWorker(actionProcessor, actualWorker);
// enqueue the completable that process actions put in reply subject
workerProcessor.onNext(actions);
// return the worker that adds actions to the reply subject
return worker;
}
static final Disposable SUBSCRIBED = new SubscribedDisposable();
static final Disposable DISPOSED = Disposable.disposed();
@SuppressWarnings("serial")
abstract static class ScheduledAction extends AtomicReference<Disposable> implements Disposable {
ScheduledAction() {
super(SUBSCRIBED);
}
void call(Worker actualWorker, CompletableObserver actionCompletable) {
Disposable oldState = get();
// either SUBSCRIBED or UNSUBSCRIBED
if (oldState == DISPOSED) {
// no need to schedule return
return;
}
if (oldState != SUBSCRIBED) {
// has already been scheduled return
// should not be able to get here but handle it anyway by not
// rescheduling.
return;
}
Disposable newState = callActual(actualWorker, actionCompletable);
if (!compareAndSet(SUBSCRIBED, newState)) {
// set would only fail if the new current state is some other
// subscription from a concurrent call to this method.
// Unsubscribe from the action just scheduled because it lost
// the race.
newState.dispose();
}
}
protected abstract Disposable callActual(Worker actualWorker, CompletableObserver actionCompletable);
@Override
public boolean isDisposed() {
return get().isDisposed();
}
@Override
public void dispose() {
getAndSet(DISPOSED).dispose();
}
}
@SuppressWarnings("serial")
static class ImmediateAction extends ScheduledAction {
private final Runnable action;
ImmediateAction(Runnable action) {
this.action = action;
}
@Override
protected Disposable callActual(Worker actualWorker, CompletableObserver actionCompletable) {
return actualWorker.schedule(new OnCompletedAction(action, actionCompletable));
}
}
@SuppressWarnings("serial")
static class DelayedAction extends ScheduledAction {
private final Runnable action;
private final long delayTime;
private final TimeUnit unit;
DelayedAction(Runnable action, long delayTime, TimeUnit unit) {
this.action = action;
this.delayTime = delayTime;
this.unit = unit;
}
@Override
protected Disposable callActual(Worker actualWorker, CompletableObserver actionCompletable) {
return actualWorker.schedule(new OnCompletedAction(action, actionCompletable), delayTime, unit);
}
}
static class OnCompletedAction implements Runnable {
final CompletableObserver actionCompletable;
final Runnable action;
OnCompletedAction(Runnable action, CompletableObserver actionCompletable) {
this.action = action;
this.actionCompletable = actionCompletable;
}
@Override
public void run() {
try {
action.run();
} finally {
actionCompletable.onComplete();
}
}
}
static final class CreateWorkerFunction implements Function<ScheduledAction, Completable> {
final Worker actualWorker;
CreateWorkerFunction(Worker actualWorker) {
this.actualWorker = actualWorker;
}
@Override
public Completable apply(final ScheduledAction action) {
return new WorkerCompletable(action);
}
final class WorkerCompletable extends Completable {
final ScheduledAction action;
WorkerCompletable(ScheduledAction action) {
this.action = action;
}
@Override
protected void subscribeActual(CompletableObserver actionCompletable) {
actionCompletable.onSubscribe(action);
action.call(actualWorker, actionCompletable);
}
}
}
static final class QueueWorker extends Worker {
private final AtomicBoolean unsubscribed;
private final FlowableProcessor<ScheduledAction> actionProcessor;
private final Worker actualWorker;
QueueWorker(FlowableProcessor<ScheduledAction> actionProcessor, Worker actualWorker) {
this.actionProcessor = actionProcessor;
this.actualWorker = actualWorker;
unsubscribed = new AtomicBoolean();
}
@Override
public void dispose() {
// complete the actionQueue when worker is unsubscribed to make
// room for the next worker in the workerQueue.
if (unsubscribed.compareAndSet(false, true)) {
actionProcessor.onComplete();
actualWorker.dispose();
}
}
@Override
public boolean isDisposed() {
return unsubscribed.get();
}
@NonNull
@Override
public Disposable schedule(@NonNull final Runnable action, final long delayTime, @NonNull final TimeUnit unit) {
// send a scheduled action to the actionQueue
DelayedAction delayedAction = new DelayedAction(action, delayTime, unit);
actionProcessor.onNext(delayedAction);
return delayedAction;
}
@NonNull
@Override
public Disposable schedule(@NonNull final Runnable action) {
// send a scheduled action to the actionQueue
ImmediateAction immediateAction = new ImmediateAction(action);
actionProcessor.onNext(immediateAction);
return immediateAction;
}
}
static final class SubscribedDisposable implements Disposable {
@Override
public void dispose() {
}
@Override
public boolean isDisposed() {
return false;
}
}
}