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/**
* 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 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;
import io.reactivex.schedulers.SchedulerRunnableIntrospection;
import java.util.concurrent.TimeUnit;
/**
* A {@code Scheduler} is an object that specifies an API for scheduling
* units of work provided in the form of {@link Runnable}s to be
* executed without delay (effectively as soon as possible), after a specified time delay or periodically
* and represents an abstraction over an asynchronous boundary that ensures
* these units of work get executed by some underlying task-execution scheme
* (such as custom Threads, event loop, {@link java.util.concurrent.Executor Executor} or Actor system)
* with some uniform properties and guarantees regardless of the particular underlying
* scheme.
*
* You can get various standard, RxJava-specific instances of this class via
* the static methods of the {@link io.reactivex.schedulers.Schedulers} utility class.
*
* The so-called {@link Worker}s of a {@code Scheduler} can be created via the {@link #createWorker()} method which allow the scheduling
* of multiple {@link Runnable} tasks in an isolated manner. {@code Runnable} tasks scheduled on a {@code Worker} are guaranteed to be
* executed sequentially and in a non-overlapping fashion. Non-delayed {@code Runnable} tasks are guaranteed to execute in a
* First-In-First-Out order but their execution may be interleaved with delayed tasks.
* In addition, outstanding or running tasks can be cancelled together via
* {@link Worker#dispose()} without affecting any other {@code Worker} instances of the same {@code Scheduler}.
*
* Implementations of the {@link #scheduleDirect} and {@link Worker#schedule} methods are encouraged to call the {@link io.reactivex.plugins.RxJavaPlugins#onSchedule(Runnable)}
* method to allow a scheduler hook to manipulate (wrap or replace) the original {@code Runnable} task before it is submitted to the
* underlying task-execution scheme.
*
* The default implementations of the {@code scheduleDirect} methods provided by this abstract class
* delegate to the respective {@code schedule} methods in the {@link Worker} instance created via {@link #createWorker()}
* for each individual {@link Runnable} task submitted. Implementors of this class are encouraged to provide
* a more efficient direct scheduling implementation to avoid the time and memory overhead of creating such {@code Worker}s
* for every task.
* This delegation is done via special wrapper instances around the original {@code Runnable} before calling the respective
* {@code Worker.schedule} method. Note that this can lead to multiple {@code RxJavaPlugins.onSchedule} calls and potentially
* multiple hooks applied. Therefore, the default implementations of {@code scheduleDirect} (and the {@link Worker#schedulePeriodically(Runnable, long, long, TimeUnit)})
* wrap the incoming {@code Runnable} into a class that implements the {@link io.reactivex.schedulers.SchedulerRunnableIntrospection}
* interface which can grant access to the original or hooked {@code Runnable}, thus, a repeated {@code RxJavaPlugins.onSchedule}
* can detect the earlier hook and not apply a new one over again.
*
* The default implementation of {@link #now(TimeUnit)} and {@link Worker#now(TimeUnit)} methods to return current
* {@link System#currentTimeMillis()} value in the desired time unit. Custom {@code Scheduler} implementations can override this
* to provide specialized time accounting (such as virtual time to be advanced programmatically).
* Note that operators requiring a {@code Scheduler} may rely on either of the {@code now()} calls provided by
* {@code Scheduler} or {@code Worker} respectively, therefore, it is recommended they represent a logically
* consistent source of the current time.
*
* The default implementation of the {@link Worker#schedulePeriodically(Runnable, long, long, TimeUnit)} method uses
* the {@link Worker#schedule(Runnable, long, TimeUnit)} for scheduling the {@code Runnable} task periodically.
* The algorithm calculates the next absolute time when the task should run again and schedules this execution
* based on the relative time between it and {@link Worker#now(TimeUnit)}. However, drifts or changes in the
* system clock could affect this calculation either by scheduling subsequent runs too frequently or too far apart.
* Therefore, the default implementation uses the {@link #clockDriftTolerance()} value (set via
* {@code rx2.scheduler.drift-tolerance} in minutes) to detect a drift in {@link Worker#now(TimeUnit)} and
* re-adjust the absolute/relative time calculation accordingly.
*
* The default implementations of {@link #start()} and {@link #shutdown()} do nothing and should be overridden if the
* underlying task-execution scheme supports stopping and restarting itself.
*
* If the {@code Scheduler} is shut down or a {@code Worker} is disposed, the {@code schedule} methods
* should return the {@link io.reactivex.disposables.Disposables#disposed()} singleton instance indicating the shut down/disposed
* state to the caller. Since the shutdown or dispose can happen from any thread, the {@code schedule} implementations
* should make best effort to cancel tasks immediately after those tasks have been submitted to the
* underlying task-execution scheme if the shutdown/dispose was detected after this submission.
*
* All methods on the {@code Scheduler} and {@code Worker} classes should be thread safe.
*/
public abstract class Scheduler {
/**
* The tolerance for a clock drift in nanoseconds where the periodic scheduler will rebase.
*
* The associated system parameter, {@code rx2.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.
*
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 sequential execution of actions.
*
* When work is completed, the {@code Worker} instance should be released
* by calling {@link Scheduler.Worker#dispose()} to avoid potential resource leaks in the
* underlying task-execution scheme.
*
* Work on a {@link Scheduler.Worker} is guaranteed to be sequential and non-overlapping.
*
* @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.
*
* Implementations should make sure the call is idempotent, thread-safe and
* should not throw any {@code RuntimeException} if it doesn't support this
* functionality.
*
* @since 2.0
*/
public void start() {
}
/**
* Instructs the Scheduler instance to stop threads,
* stop accepting tasks on any outstanding {@link Worker} instances
* and clean up any associated resources with this Scheduler.
*
* Implementations should make sure the call is idempotent, thread-safe and
* should not throw any {@code RuntimeException} if it doesn't support this
* functionality.
* @since 2.0
*/
public void shutdown() {
}
/**
* Schedules the given task on this Scheduler without any time delay.
*
*
* This method is safe to be called from multiple threads but there are no
* ordering or non-overlapping 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 time delay.
*
*
* 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 time delay and repeat period.
*
*
* This method is safe to be called from multiple threads but there are no
* ordering guarantees between tasks.
*
*
* The periodic execution is at a fixed rate, that is, the first execution will be after the
* {@code initialDelay}, the second after {@code initialDelay + period}, the third after
* {@code 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.
*
* 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.
*
* Finally the actions scheduled on the parent {@link Scheduler} when the
* inner most {@link Completable}s are subscribed to.
*
* 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.
*
* Limit the amount concurrency two at a time without creating a new fix
* size thread pool:
*
*
* 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);
* });
*
*
* 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.
*
*
* 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));
* });
*
*
* 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).
*
*
* 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));
* }));
* });
*
*
* History: 2.0.1 - experimental
* @param 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 when(@NonNull Function>, Completable> combine) {
return (S) new SchedulerWhen(combine, this);
}
/**
* Represents an isolated, sequential worker of a parent Scheduler for executing {@code Runnable} tasks on
* an underlying task-execution scheme (such as custom Threads, event loop, {@link java.util.concurrent.Executor Executor} or Actor system).
*
* Disposing the {@link Worker} should cancel all outstanding work and allows resource cleanup.
*
* The default implementations of {@link #schedule(Runnable)} and {@link #schedulePeriodically(Runnable, long, long, TimeUnit)}
* delegate to the abstract {@link #schedule(Runnable, long, TimeUnit)} method. Its implementation is encouraged to
* track the individual {@code Runnable} tasks while they are waiting to be executed (with or without delay) so that
* {@link #dispose()} can prevent their execution or potentially interrupt them if they are currently running.
*
* The default implementation of the {@link #now(TimeUnit)} method returns current
* {@link System#currentTimeMillis()} value in the desired time unit. Custom {@code Worker} implementations can override this
* to provide specialized time accounting (such as virtual time to be advanced programmatically).
* Note that operators requiring a scheduler may rely on either of the {@code now()} calls provided by
* {@code Scheduler} or {@code Worker} respectively, therefore, it is recommended they represent a logically
* consistent source of the current time.
*
* The default implementation of the {@link #schedulePeriodically(Runnable, long, long, TimeUnit)} method uses
* the {@link #schedule(Runnable, long, TimeUnit)} for scheduling the {@code Runnable} task periodically.
* The algorithm calculates the next absolute time when the task should run again and schedules this execution
* based on the relative time between it and {@link #now(TimeUnit)}. However, drifts or changes in the
* system clock would affect this calculation either by scheduling subsequent runs too frequently or too far apart.
* Therefore, the default implementation uses the {@link #clockDriftTolerance()} value (set via
* {@code rx2.scheduler.drift-tolerance} in minutes) to detect a drift in {@link #now(TimeUnit)} and
* re-adjust the absolute/relative time calculation accordingly.
*
* If the {@code Worker} is disposed, the {@code schedule} methods
* should return the {@link io.reactivex.disposables.Disposables#disposed()} singleton instance indicating the disposed
* state to the caller. Since the {@link #dispose()} call can happen on any thread, the {@code schedule} implementations
* should make best effort to cancel tasks immediately after those tasks have been submitted to the
* underlying task-execution scheme if the dispose was detected after this submission.
*
* All methods on the {@code Worker} class should be thread safe.
*/
public abstract static class Worker implements Disposable {
/**
* Schedules a Runnable for execution without any time delay.
*
*
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 specified by a time delay
* relative to the current time.
*
* 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 periodic execution of the given task with the given initial time delay and repeat period.
*
* The default implementation schedules and reschedules the {@code Runnable} task via the
* {@link #schedule(Runnable, long, TimeUnit)}
* method over and over and at a fixed rate, that is, the first execution will be after the
* {@code initialDelay}, the second after {@code initialDelay + period}, the third after
* {@code initialDelay + 2 * period}, and so on.
*
* Note to implementors: non-positive {@code initialTime} and {@code period} should be regarded as
* non-delayed scheduling of the first and any subsequent executions.
* In addition, a more specific {@code Worker} implementation should override this method
* if it can perform the periodic task execution with less overhead (such as by avoiding the
* creation of the wrapper and tracker objects upon each periodic invocation of the
* common {@link #schedule(Runnable, long, TimeUnit)} method).
*
* @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, SchedulerRunnableIntrospection {
@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));
}
}
@Override
public Runnable getWrappedRunnable() {
return this.decoratedRun;
}
}
}
static final class PeriodicDirectTask
implements Disposable, Runnable, SchedulerRunnableIntrospection {
@NonNull
final Runnable run;
@NonNull
final Worker worker;
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;
}
@Override
public Runnable getWrappedRunnable() {
return run;
}
}
static final class DisposeTask implements Disposable, Runnable, SchedulerRunnableIntrospection {
@NonNull
final Runnable decoratedRun;
@NonNull
final Worker w;
@Nullable
Thread runner;
DisposeTask(@NonNull Runnable decoratedRun, @NonNull 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();
}
@Override
public Runnable getWrappedRunnable() {
return this.decoratedRun;
}
}
}