/**
* 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;
import java.util.concurrent.TimeUnit;
import io.reactivex.annotations.*;
import io.reactivex.disposables.Disposable;
import io.reactivex.exceptions.Exceptions;
import io.reactivex.functions.Function;
import io.reactivex.internal.disposables.*;
import io.reactivex.internal.schedulers.*;
import io.reactivex.internal.util.ExceptionHelper;
import io.reactivex.plugins.RxJavaPlugins;
/**
* A {@code Scheduler} is an object that specifies an API for scheduling
* units of work with or without delays or periodically.
* You can get common instances of this class in {@link io.reactivex.schedulers.Schedulers}.
*/
public abstract class Scheduler {
/**
* The tolerance for a clock drift in nanoseconds where the periodic scheduler will rebase.
* <p>
* The associated system parameter, {@code rx.scheduler.drift-tolerance}, expects its value in minutes.
*/
static final long CLOCK_DRIFT_TOLERANCE_NANOSECONDS;
static {
CLOCK_DRIFT_TOLERANCE_NANOSECONDS = TimeUnit.MINUTES.toNanos(
Long.getLong("rx2.scheduler.drift-tolerance", 15));
}
/**
* Returns the clock drift tolerance in nanoseconds.
* <p>Related system property: {@code rx2.scheduler.drift-tolerance} in minutes
* @return the tolerance in nanoseconds
* @since 2.0
*/
public static long clockDriftTolerance() {
return CLOCK_DRIFT_TOLERANCE_NANOSECONDS;
}
/**
* Retrieves or creates a new {@link Scheduler.Worker} that represents serial execution of actions.
* <p>
* When work is completed it should be unsubscribed using {@link Scheduler.Worker#dispose()}.
* <p>
* Work on a {@link Scheduler.Worker} is guaranteed to be sequential.
*
* @return a Worker representing a serial queue of actions to be executed
*/
@NonNull
public abstract Worker createWorker();
/**
* Returns the 'current time' of the Scheduler in the specified time unit.
* @param unit the time unit
* @return the 'current time'
* @since 2.0
*/
public long now(@NonNull TimeUnit unit) {
return unit.convert(System.currentTimeMillis(), TimeUnit.MILLISECONDS);
}
/**
* Allows the Scheduler instance to start threads
* and accept tasks on them.
* <p>Implementations should make sure the call is idempotent and thread-safe.
* @since 2.0
*/
public void start() {
}
/**
* Instructs the Scheduler instance to stop threads
* and stop accepting tasks on any outstanding Workers.
* <p>Implementations should make sure the call is idempotent and thread-safe.
* @since 2.0
*/
public void shutdown() {
}
/**
* Schedules the given task on this scheduler non-delayed execution.
*
* <p>
* This method is safe to be called from multiple threads but there are no
* ordering guarantees between tasks.
*
* @param run the task to execute
*
* @return the Disposable instance that let's one cancel this particular task.
* @since 2.0
*/
@NonNull
public Disposable scheduleDirect(@NonNull Runnable run) {
return scheduleDirect(run, 0L, TimeUnit.NANOSECONDS);
}
/**
* Schedules the execution of the given task with the given delay amount.
*
* <p>
* This method is safe to be called from multiple threads but there are no
* ordering guarantees between tasks.
*
* @param run the task to schedule
* @param delay the delay amount, non-positive values indicate non-delayed scheduling
* @param unit the unit of measure of the delay amount
* @return the Disposable that let's one cancel this particular delayed task.
* @since 2.0
*/
@NonNull
public Disposable scheduleDirect(@NonNull Runnable run, long delay, @NonNull TimeUnit unit) {
final Worker w = createWorker();
final Runnable decoratedRun = RxJavaPlugins.onSchedule(run);
DisposeTask task = new DisposeTask(decoratedRun, w);
w.schedule(task, delay, unit);
return task;
}
/**
* Schedules a periodic execution of the given task with the given initial delay and period.
*
* <p>
* This method is safe to be called from multiple threads but there are no
* ordering guarantees between tasks.
*
* <p>
* The periodic execution is at a fixed rate, that is, the first execution will be after the initial
* delay, the second after initialDelay + period, the third after initialDelay + 2 * period, and so on.
*
* @param run the task to schedule
* @param initialDelay the initial delay amount, non-positive values indicate non-delayed scheduling
* @param period the period at which the task should be re-executed
* @param unit the unit of measure of the delay amount
* @return the Disposable that let's one cancel this particular delayed task.
* @since 2.0
*/
@NonNull
public Disposable schedulePeriodicallyDirect(@NonNull Runnable run, long initialDelay, long period, @NonNull TimeUnit unit) {
final Worker w = createWorker();
final Runnable decoratedRun = RxJavaPlugins.onSchedule(run);
PeriodicDirectTask periodicTask = new PeriodicDirectTask(decoratedRun, w);
Disposable d = w.schedulePeriodically(periodicTask, initialDelay, period, unit);
if (d == EmptyDisposable.INSTANCE) {
return d;
}
return periodicTask;
}
/**
* 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 Flowable} of {@link Flowable}
* of {@link Completable}s into just one {@link Completable}. There must be
* a chain of operators connecting the returned value to the source
* {@link Flowable} otherwise any work scheduled on the returned
* {@link Scheduler} will not be executed.
* <p>
* When {@link Scheduler#createWorker()} is invoked a {@link Flowable} of
* {@link Completable}s is onNext'd to the combinator to be flattened. If
* the inner {@link Flowable} is not immediately subscribed to an calls to
* {@link Worker#schedule} are buffered. Once the {@link Flowable} 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 Worker} is unsubscribed the {@link Completable} emits an
* onComplete and triggers any behavior in the flattening operator. The
* {@link Flowable} 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>
* Scheduler limitScheduler = Schedulers.computation().when(workers -> {
* // use merge max concurrent to limit the number of concurrent
* // callbacks two at a time
* return Completable.merge(Flowable.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 Worker}s rather than individual
* actions. Generally each {@link Flowable} uses its own {@link 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.functions.BiFunction)} where
* subscribing to the first {@link Flowable} could deadlock the
* subscription to the second.
*
* <pre>
* Scheduler limitScheduler = Schedulers.computation().when(workers -> {
* // use merge max concurrent to limit the number of concurrent
* // Flowables two at a time
* return Completable.merge(Flowable.merge(workers, 2));
* });
* </pre>
*
* 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 Flowable}
* operator that limits the rate without dropping the values (aka leaky
* bucket algorithm).
*
* <pre>
* 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
* @param <S> a Scheduler and a Subscription
* @param combine the function that takes a two-level nested Flowable sequence of a Completable and returns
* the Completable that will be subscribed to and should trigger the execution of the scheduled Actions.
* @return the Scheduler with the customized execution behavior
* @since 2.1
*/
@SuppressWarnings("unchecked")
@NonNull
public <S extends Scheduler & Disposable> S when(@NonNull Function<Flowable<Flowable<Completable>>, Completable> combine) {
return (S) new SchedulerWhen(combine, this);
}
/**
* Sequential Scheduler for executing actions on a single thread or event loop.
* <p>
* Disposing the {@link Worker} cancels all outstanding work and allows resource cleanup.
*/
public abstract static class Worker implements Disposable {
/**
* Schedules a Runnable for execution without delay.
*
* <p>The default implementation delegates to {@link #schedule(Runnable, long, TimeUnit)}.
*
* @param run
* Runnable to schedule
* @return a Disposable to be able to unsubscribe the action (cancel it if not executed)
*/
@NonNull
public Disposable schedule(@NonNull Runnable run) {
return schedule(run, 0L, TimeUnit.NANOSECONDS);
}
/**
* Schedules an Runnable for execution at some point in the future.
* <p>
* Note to implementors: non-positive {@code delayTime} should be regarded as non-delayed schedule, i.e.,
* as if the {@link #schedule(Runnable)} was called.
*
* @param run
* the Runnable to schedule
* @param delay
* time to wait before executing the action; non-positive values indicate an non-delayed
* schedule
* @param unit
* the time unit of {@code delayTime}
* @return a Disposable to be able to unsubscribe the action (cancel it if not executed)
*/
@NonNull
public abstract Disposable schedule(@NonNull Runnable run, long delay, @NonNull TimeUnit unit);
/**
* Schedules a cancelable action to be executed periodically. This default implementation schedules
* recursively and waits for actions to complete (instead of potentially executing long-running actions
* concurrently). Each scheduler that can do periodic scheduling in a better way should override this.
* <p>
* Note to implementors: non-positive {@code initialTime} and {@code period} should be regarded as
* non-delayed scheduling of the first and any subsequent executions.
*
* @param run
* the Runnable to execute periodically
* @param initialDelay
* time to wait before executing the action for the first time; non-positive values indicate
* an non-delayed schedule
* @param period
* the time interval to wait each time in between executing the action; non-positive values
* indicate no delay between repeated schedules
* @param unit
* the time unit of {@code period}
* @return a Disposable to be able to unsubscribe the action (cancel it if not executed)
*/
@NonNull
public Disposable schedulePeriodically(@NonNull Runnable run, final long initialDelay, final long period, @NonNull final TimeUnit unit) {
final SequentialDisposable first = new SequentialDisposable();
final SequentialDisposable sd = new SequentialDisposable(first);
final Runnable decoratedRun = RxJavaPlugins.onSchedule(run);
final long periodInNanoseconds = unit.toNanos(period);
final long firstNowNanoseconds = now(TimeUnit.NANOSECONDS);
final long firstStartInNanoseconds = firstNowNanoseconds + unit.toNanos(initialDelay);
Disposable d = schedule(new PeriodicTask(firstStartInNanoseconds, decoratedRun, firstNowNanoseconds, sd,
periodInNanoseconds), initialDelay, unit);
if (d == EmptyDisposable.INSTANCE) {
return d;
}
first.replace(d);
return sd;
}
/**
* Returns the 'current time' of the Worker in the specified time unit.
* @param unit the time unit
* @return the 'current time'
* @since 2.0
*/
public long now(@NonNull TimeUnit unit) {
return unit.convert(System.currentTimeMillis(), TimeUnit.MILLISECONDS);
}
/**
* Holds state and logic to calculate when the next delayed invocation
* of this task has to happen (accounting for clock drifts).
*/
final class PeriodicTask implements Runnable {
@NonNull
final Runnable decoratedRun;
@NonNull
final SequentialDisposable sd;
final long periodInNanoseconds;
long count;
long lastNowNanoseconds;
long startInNanoseconds;
PeriodicTask(long firstStartInNanoseconds, @NonNull Runnable decoratedRun,
long firstNowNanoseconds, @NonNull SequentialDisposable sd, long periodInNanoseconds) {
this.decoratedRun = decoratedRun;
this.sd = sd;
this.periodInNanoseconds = periodInNanoseconds;
lastNowNanoseconds = firstNowNanoseconds;
startInNanoseconds = firstStartInNanoseconds;
}
@Override
public void run() {
decoratedRun.run();
if (!sd.isDisposed()) {
long nextTick;
long nowNanoseconds = now(TimeUnit.NANOSECONDS);
// If the clock moved in a direction quite a bit, rebase the repetition period
if (nowNanoseconds + CLOCK_DRIFT_TOLERANCE_NANOSECONDS < lastNowNanoseconds
|| nowNanoseconds >= lastNowNanoseconds + periodInNanoseconds + CLOCK_DRIFT_TOLERANCE_NANOSECONDS) {
nextTick = nowNanoseconds + periodInNanoseconds;
/*
* Shift the start point back by the drift as if the whole thing
* started count periods ago.
*/
startInNanoseconds = nextTick - (periodInNanoseconds * (++count));
} else {
nextTick = startInNanoseconds + (++count * periodInNanoseconds);
}
lastNowNanoseconds = nowNanoseconds;
long delay = nextTick - nowNanoseconds;
sd.replace(schedule(this, delay, TimeUnit.NANOSECONDS));
}
}
}
}
static class PeriodicDirectTask
implements Runnable, Disposable {
final Runnable run;
@NonNull
final Worker worker;
@NonNull
volatile boolean disposed;
PeriodicDirectTask(@NonNull Runnable run, @NonNull Worker worker) {
this.run = run;
this.worker = worker;
}
@Override
public void run() {
if (!disposed) {
try {
run.run();
} catch (Throwable ex) {
Exceptions.throwIfFatal(ex);
worker.dispose();
throw ExceptionHelper.wrapOrThrow(ex);
}
}
}
@Override
public void dispose() {
disposed = true;
worker.dispose();
}
@Override
public boolean isDisposed() {
return disposed;
}
}
static final class DisposeTask implements Runnable, Disposable {
final Runnable decoratedRun;
final Worker w;
Thread runner;
DisposeTask(Runnable decoratedRun, Worker w) {
this.decoratedRun = decoratedRun;
this.w = w;
}
@Override
public void run() {
runner = Thread.currentThread();
try {
decoratedRun.run();
} finally {
dispose();
runner = null;
}
}
@Override
public void dispose() {
if (runner == Thread.currentThread() && w instanceof NewThreadWorker) {
((NewThreadWorker)w).shutdown();
} else {
w.dispose();
}
}
@Override
public boolean isDisposed() {
return w.isDisposed();
}
}
}