rx.internal.schedulers.SchedulerWhen Maven / Gradle / Ivy
/**
* Copyright 2016 Netflix, Inc.
*
* 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 rx.internal.schedulers;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicReference;
import rx.Completable;
import rx.Completable.OnSubscribe;
import rx.CompletableSubscriber;
import rx.Observable;
import rx.Observer;
import rx.Scheduler;
import rx.Subscription;
import rx.annotations.Experimental;
import rx.functions.Action0;
import rx.functions.Func1;
import rx.internal.operators.BufferUntilSubscriber;
import rx.observers.SerializedObserver;
import rx.subjects.PublishSubject;
import rx.subscriptions.Subscriptions;
/**
* 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.
*
* 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.
*
* Finally the actions scheduled on the parent {@link Scheduler} when the inner
* most {@link Completable}s are subscribed to.
*
* When the {@link rx.Scheduler.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.
*
* Limit the amount concurrency two at a time without creating a new fix size
* thread pool:
*
*
* Scheduler limitSched = 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);
* });
*
*
* 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 rx.Scheduler.Worker}s rather than individual actions.
* Generally each {@link Observable} uses its own {@link rx.Scheduler.Worker}. This means
* that this will essentially limit the number of concurrent subscribes. The
* danger comes from using operators like
* {@link Observable#zip(Observable, Observable, rx.functions.Func2)} where
* subscribing to the first {@link Observable} could deadlock the subscription
* to the second.
*
*
* Scheduler limitSched = 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));
* });
*
*
* Slowing down the rate to no more than 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).
*
*
* Scheduler slowSched = 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));
* }));
* });
*
*/
@Experimental
public class SchedulerWhen extends Scheduler implements Subscription {
private final Scheduler actualScheduler;
private final Observer> workerObserver;
private final Subscription subscription;
public SchedulerWhen(Func1>, Completable> combine, Scheduler actualScheduler) {
this.actualScheduler = actualScheduler;
// workers are converted into completables and put in this queue.
PublishSubject> workerSubject = PublishSubject.create();
this.workerObserver = new SerializedObserver>(workerSubject);
// send it to a custom combinator to pick the order and rate at which
// workers are processed.
this.subscription = combine.call(workerSubject.onBackpressureBuffer()).subscribe();
}
@Override
public void unsubscribe() {
subscription.unsubscribe();
}
@Override
public boolean isUnsubscribed() {
return subscription.isUnsubscribed();
}
@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.
BufferUntilSubscriber actionSubject = BufferUntilSubscriber.create();
final Observer actionObserver = new SerializedObserver(actionSubject);
// convert the work of scheduling all the actions into a completable
Observable actions = actionSubject.map(new Func1() {
@Override
public Completable call(final ScheduledAction action) {
return Completable.create(new OnSubscribe() {
@Override
public void call(CompletableSubscriber actionCompletable) {
actionCompletable.onSubscribe(action);
action.call(actualWorker);
actionCompletable.onCompleted();
}
});
}
});
// a worker that queues the action to the actionQueue subject.
Worker worker = new Worker() {
private final AtomicBoolean unsubscribed = new AtomicBoolean();
@Override
public void unsubscribe() {
// complete the actionQueue when worker is unsubscribed to make
// room for the next worker in the workerQueue.
if (unsubscribed.compareAndSet(false, true)) {
actualWorker.unsubscribe();
actionObserver.onCompleted();
}
}
@Override
public boolean isUnsubscribed() {
return unsubscribed.get();
}
@Override
public Subscription schedule(final Action0 action, final long delayTime, final TimeUnit unit) {
// send a scheduled action to the actionQueue
DelayedAction delayedAction = new DelayedAction(action, delayTime, unit);
actionObserver.onNext(delayedAction);
return delayedAction;
}
@Override
public Subscription schedule(final Action0 action) {
// send a scheduled action to the actionQueue
ImmediateAction immediateAction = new ImmediateAction(action);
actionObserver.onNext(immediateAction);
return immediateAction;
}
};
// enqueue the completable that process actions put in reply subject
workerObserver.onNext(actions);
// return the worker that adds actions to the reply subject
return worker;
}
private static final Subscription SUBSCRIBED = new Subscription() {
@Override
public void unsubscribe() {
}
@Override
public boolean isUnsubscribed() {
return false;
}
};
private static final Subscription UNSUBSCRIBED = Subscriptions.unsubscribed();
@SuppressWarnings("serial")
private static abstract class ScheduledAction extends AtomicReference implements Subscription {
public ScheduledAction() {
super(SUBSCRIBED);
}
private final void call(Worker actualWorker) {
Subscription oldState = get();
// either SUBSCRIBED or UNSUBSCRIBED
if (oldState == UNSUBSCRIBED) {
// 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;
}
Subscription newState = callActual(actualWorker);
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.unsubscribe();
}
}
protected abstract Subscription callActual(Worker actualWorker);
@Override
public boolean isUnsubscribed() {
return get().isUnsubscribed();
}
@Override
public void unsubscribe() {
Subscription oldState;
// no matter what the current state is the new state is going to be
Subscription newState = UNSUBSCRIBED;
do {
oldState = get();
if (oldState == UNSUBSCRIBED) {
// the action has already been unsubscribed
return;
}
} while (!compareAndSet(oldState, newState));
if (oldState != SUBSCRIBED) {
// the action was scheduled. stop it.
oldState.unsubscribe();
}
}
}
@SuppressWarnings("serial")
private static class ImmediateAction extends ScheduledAction {
private final Action0 action;
public ImmediateAction(Action0 action) {
this.action = action;
}
@Override
protected Subscription callActual(Worker actualWorker) {
return actualWorker.schedule(action);
}
}
@SuppressWarnings("serial")
private static class DelayedAction extends ScheduledAction {
private final Action0 action;
private final long delayTime;
private final TimeUnit unit;
public DelayedAction(Action0 action, long delayTime, TimeUnit unit) {
this.action = action;
this.delayTime = delayTime;
this.unit = unit;
}
@Override
protected Subscription callActual(Worker actualWorker) {
return actualWorker.schedule(action, delayTime, unit);
}
}
}
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