* 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
* 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;
}
}
}
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