Class Schedulers

java.lang.Object
io.reactivex.rxjava4.schedulers.Schedulers
public final class Schedulers extends Object
Static factory methods for returning standard Scheduler instances.

The initial and runtime values of the various scheduler types can be overridden via the RxJavaPlugins.setInit(scheduler name)SchedulerHandler() and RxJavaPlugins.set(scheduler name)SchedulerHandler() respectively. Note that overriding any initial Scheduler via the RxJavaPlugins has to happen before the Schedulers class is accessed.

Supported system properties (System.getProperty()):

  • rx3.io-keep-alive-time (long): sets the keep-alive time of the io() Scheduler workers, default is IoScheduler.KEEP_ALIVE_TIME_DEFAULT
  • rx3.io-priority (int): sets the thread priority of the io() Scheduler, default is Thread.NORM_PRIORITY
  • rx3.io-scheduled-release (boolean): true sets the worker release mode of the io() Scheduler to scheduled, default is false for eager mode.
  • rx3.computation-threads (int): sets the number of threads in the computation() Scheduler, default is the number of available CPUs
  • rx3.computation-priority (int): sets the thread priority of the computation() Scheduler, default is Thread.NORM_PRIORITY
  • rx3.newthread-priority (int): sets the thread priority of the newThread() Scheduler, default is Thread.NORM_PRIORITY
  • rx3.single-priority (int): sets the thread priority of the single() Scheduler, default is Thread.NORM_PRIORITY
  • rx3.purge-enabled (boolean): enables purging of all Scheduler's backing thread pools, default is true
  • rx3.scheduler.use-nanotime (boolean): true instructs Scheduler to use System.nanoTime() for Scheduler.now(TimeUnit), instead of default System.currentTimeMillis() (false)

  • Method Details

    • computation

      @NonNull public static @NonNull Scheduler computation()
      Returns a default, shared Scheduler instance intended for computational work.

      This can be used for event-loops, processing callbacks and other computational work.

      It is not recommended to perform blocking, IO-bound work on this scheduler. Use io() instead.

      The default instance has a backing pool of single-threaded ScheduledExecutorService instances equal to the number of available processors (Runtime.availableProcessors()) to the Java VM.

      Unhandled errors will be delivered to the scheduler Thread's Thread.UncaughtExceptionHandler.

      This type of scheduler is less sensitive to leaking Scheduler.Worker instances, although not disposing a worker that has timed/delayed tasks not cancelled by other means may leak resources and/or execute those tasks "unexpectedly".

      If the RxJavaPlugins.setFailOnNonBlockingScheduler(boolean) is set to true, attempting to execute operators that block while running on this scheduler will throw an IllegalStateException.

      You can control certain properties of this standard scheduler via system properties that have to be set before the Schedulers class is referenced in your code.

      Supported system properties (System.getProperty()):

      • rx3.computation-threads (int): sets the number of threads in the computation() Scheduler, default is the number of available CPUs
      • rx3.computation-priority (int): sets the thread priority of the computation() Scheduler, default is Thread.NORM_PRIORITY

      The default value of this scheduler can be overridden at initialization time via the RxJavaPlugins.setInitComputationSchedulerHandler(io.reactivex.rxjava4.functions.Function) plugin method. Note that due to possible initialization cycles, using any of the other scheduler-returning methods will result in a NullPointerException. Once the Schedulers class has been initialized, you can override the returned Scheduler instance via the RxJavaPlugins.setComputationSchedulerHandler(io.reactivex.rxjava4.functions.Function) method.

      It is possible to create a fresh instance of this scheduler with a custom ThreadFactory, via the RxJavaPlugins.createComputationScheduler(ThreadFactory) method. Note that such custom instances require a manual call to Scheduler.shutdown() to allow the JVM to exit or the (J2EE) container to unload properly.

      Operators on the base reactive classes that use this scheduler are marked with the @SchedulerSupport(COMPUTATION) annotation.

      Returns:
      a Scheduler meant for computation-bound work

    • io

      @NonNull public static @NonNull Scheduler io()
      Returns a default, shared Scheduler instance intended for IO-bound work.

      This can be used for asynchronously performing blocking IO.

      The implementation is backed by a pool of single-threaded ScheduledExecutorService instances that will try to reuse previously started instances used by the worker returned by Scheduler.createWorker() but otherwise will start a new backing ScheduledExecutorService instance. Note that this scheduler may create an unbounded number of worker threads that can result in system slowdowns or OutOfMemoryError. Therefore, for casual uses or when implementing an operator, the Worker instances must be disposed via Disposable.dispose().

      It is not recommended to perform computational work on this scheduler. Use computation() instead.

      Unhandled errors will be delivered to the scheduler Thread's Thread.UncaughtExceptionHandler.

      You can control certain properties of this standard scheduler via system properties that have to be set before the Schedulers class is referenced in your code.

      Supported system properties (System.getProperty()):

      • rx3.io-keep-alive-time (long): sets the keep-alive time of the io() Scheduler workers, default is IoScheduler.KEEP_ALIVE_TIME_DEFAULT
      • rx3.io-priority (int): sets the thread priority of the io() Scheduler, default is Thread.NORM_PRIORITY
      • rx3.io-scheduled-release (boolean): true sets the worker release mode of the #io() Scheduler to scheduled, default is false for eager mode.

      The default value of this scheduler can be overridden at initialization time via the RxJavaPlugins.setInitIoSchedulerHandler(io.reactivex.rxjava4.functions.Function) plugin method. Note that due to possible initialization cycles, using any of the other scheduler-returning methods will result in a NullPointerException. Once the Schedulers class has been initialized, you can override the returned Scheduler instance via the RxJavaPlugins.setIoSchedulerHandler(io.reactivex.rxjava4.functions.Function) method.

      It is possible to create a fresh instance of this scheduler with a custom ThreadFactory, via the RxJavaPlugins.createIoScheduler(ThreadFactory) method. Note that such custom instances require a manual call to Scheduler.shutdown() to allow the JVM to exit or the (J2EE) container to unload properly.

      Operators on the base reactive classes that use this scheduler are marked with the @SchedulerSupport(IO) annotation.

      When the Scheduler.Worker is disposed, the underlying worker can be released to the cached worker pool in two modes:

      • In eager mode (default), the underlying worker is returned immediately to the cached worker pool and can be reused much quicker by operators. The drawback is that if the currently running task doesn't respond to interruption in time or at all, this may lead to delays or deadlock with the reuse use of the underlying worker.
      • In scheduled mode (enabled via the system parameter rx3.io-scheduled-release set to true), the underlying worker is returned to the cached worker pool only after the currently running task has finished. This can help prevent premature reuse of the underlying worker and likely won't lead to delays or deadlock with such reuses. The drawback is that the delay in release may lead to an excess amount of underlying workers being created.
      Returns:
      a Scheduler meant for IO-bound work

    • trampoline

      @NonNull public static @NonNull Scheduler trampoline()
      Returns a default, shared Scheduler instance whose Scheduler.Worker instances queue work and execute them in a FIFO manner on one of the participating threads.

      The default implementation's Scheduler.scheduleDirect(Runnable) methods execute the tasks on the current thread without any queueing and the timed overloads use blocking sleep as well.

      Note that this scheduler can't be reliably used to return the execution of tasks to the "main" thread. Such behavior requires a blocking-queueing scheduler currently not provided by RxJava itself but may be found in external libraries.

      This scheduler can't be overridden via an RxJavaPlugins method.

      Returns:
      a Scheduler that queues work on the current thread

    • newThread

      @NonNull public static @NonNull Scheduler newThread()
      Returns a default, shared Scheduler instance that creates a new Thread for each unit of work.

      The default implementation of this scheduler creates a new, single-threaded ScheduledExecutorService for each invocation of the Scheduler.scheduleDirect(Runnable) (plus its overloads) and Scheduler.createWorker() methods, thus an unbounded number of worker threads may be created that can result in system slowdowns or OutOfMemoryError. Therefore, for casual uses or when implementing an operator, the Worker instances must be disposed via Disposable.dispose().

      Unhandled errors will be delivered to the scheduler Thread's Thread.UncaughtExceptionHandler.

      You can control certain properties of this standard scheduler via system properties that have to be set before the Schedulers class is referenced in your code.

      Supported system properties (System.getProperty()):

      • rx3.newthread-priority (int): sets the thread priority of the newThread() Scheduler, default is Thread.NORM_PRIORITY

      The default value of this scheduler can be overridden at initialization time via the RxJavaPlugins.setInitNewThreadSchedulerHandler(io.reactivex.rxjava4.functions.Function) plugin method. Note that due to possible initialization cycles, using any of the other scheduler-returning methods will result in a NullPointerException. Once the Schedulers class has been initialized, you can override the returned Scheduler instance via the RxJavaPlugins.setNewThreadSchedulerHandler(io.reactivex.rxjava4.functions.Function) method.

      It is possible to create a fresh instance of this scheduler with a custom ThreadFactory, via the RxJavaPlugins.createNewThreadScheduler(ThreadFactory) method. Note that such custom instances require a manual call to Scheduler.shutdown() to allow the JVM to exit or the (J2EE) container to unload properly.

      Operators on the base reactive classes that use this scheduler are marked with the @SchedulerSupport(NEW_TRHEAD) annotation.

      Returns:
      a Scheduler that creates new threads

    • single

      @NonNull public static @NonNull Scheduler single()
      Returns a default, shared, single-thread-backed Scheduler instance for work requiring strongly-sequential execution on the same background thread.

      Uses:

      • event loop
      • support Schedulers.from(Executor) and from(ExecutorService) with delayed scheduling
      • support benchmarks that pipeline data from some thread to another thread and avoid core-bashing of computation's round-robin nature

      Unhandled errors will be delivered to the scheduler Thread's Thread.UncaughtExceptionHandler.

      This type of scheduler is less sensitive to leaking Scheduler.Worker instances, although not disposing a worker that has timed/delayed tasks not cancelled by other means may leak resources and/or execute those tasks "unexpectedly".

      If the RxJavaPlugins.setFailOnNonBlockingScheduler(boolean) is set to true, attempting to execute operators that block while running on this scheduler will throw an IllegalStateException.

      You can control certain properties of this standard scheduler via system properties that have to be set before the Schedulers class is referenced in your code.

      Supported system properties (System.getProperty()):

      • rx3.single-priority (int): sets the thread priority of the single() Scheduler, default is Thread.NORM_PRIORITY

      The default value of this scheduler can be overridden at initialization time via the RxJavaPlugins.setInitSingleSchedulerHandler(io.reactivex.rxjava4.functions.Function) plugin method. Note that due to possible initialization cycles, using any of the other scheduler-returning methods will result in a NullPointerException. Once the Schedulers class has been initialized, you can override the returned Scheduler instance via the RxJavaPlugins.setSingleSchedulerHandler(io.reactivex.rxjava4.functions.Function) method.

      It is possible to create a fresh instance of this scheduler with a custom ThreadFactory, via the RxJavaPlugins.createSingleScheduler(ThreadFactory) method. Note that such custom instances require a manual call to Scheduler.shutdown() to allow the JVM to exit or the (J2EE) container to unload properly.

      Operators on the base reactive classes that use this scheduler are marked with the @SchedulerSupport(SINGLE) annotation.

      Returns:
      a Scheduler that shares a single backing thread.
      Since:
      2.0

    • from

      @NonNull public static @NonNull Scheduler from(@NonNull @NonNull Executor executor)
      Wraps an Executor into a new Scheduler instance and delegates schedule() calls to it.

      If the provided executor doesn't support any of the more specific standard Java executor APIs, tasks scheduled by this scheduler can't be interrupted when they are executing but only prevented from running prior to that. In addition, tasks scheduled with a time delay or periodically will use the single() scheduler for the timed waiting before posting the actual task to the given executor.

      Tasks submitted to the Scheduler.Worker of this Scheduler are also not interruptible. Use the from(Executor, boolean) overload to enable task interruption via this wrapper.

      If the provided executor supports the standard Java ExecutorService API, tasks scheduled by this scheduler can be cancelled/interrupted by calling Disposable.dispose(). In addition, tasks scheduled with a time delay or periodically will use the single() scheduler for the timed waiting before posting the actual task to the given executor.

      If the provided executor supports the standard Java ScheduledExecutorService API, tasks scheduled by this scheduler can be cancelled/interrupted by calling Disposable.dispose(). In addition, tasks scheduled with a time delay or periodically will use the provided executor. Note, however, if the provided ScheduledExecutorService instance is not single threaded, tasks scheduled with a time delay close to each other may end up executing in different order than the original schedule() call was issued. This limitation may be lifted in a future patch.

      The implementation of the Worker of this wrapper Scheduler is eager and will execute as many non-delayed tasks as it can, which may result in a longer than expected occupation of a thread of the given backing Executor. In other terms, it does not allow per-Runnable fairness in case the worker runs on a shared underlying thread of the Executor. See from(Executor, boolean, boolean) to create a wrapper that uses the underlying Executor more fairly.

      Starting, stopping and restarting this scheduler is not supported (no-op) and the provided executor's lifecycle must be managed externally: 

      ExecutorService exec = Executors.newSingleThreadedExecutor();
try {
    Scheduler scheduler = Schedulers.from(exec);
    Flowable.just(1)
       .subscribeOn(scheduler)
       .map(v -> v + 1)
       .observeOn(scheduler)
       .blockingSubscribe(System.out::println);
} finally {
    exec.shutdown();
}

      Note that the provided Executor should avoid throwing a RejectedExecutionException (for example, by shutting it down prematurely or using a bounded-queue ExecutorService) because such circumstances prevent RxJava from progressing flow-related activities correctly. If the Executor.execute(Runnable) or ExecutorService.submit(Callable) throws, the RejectedExecutionException is routed to the global error handler via RxJavaPlugins.onError(Throwable). To avoid shutdown-related problems, it is recommended all flows using the returned Scheduler to be canceled/disposed before the underlying Executor is shut down. To avoid problems due to the Executor having a bounded-queue, it is recommended to rephrase the flow to utilize backpressure as the means to limit outstanding work.

      This type of scheduler is less sensitive to leaking Scheduler.Worker instances, although not disposing a worker that has timed/delayed tasks not cancelled by other means may leak resources and/or execute those tasks "unexpectedly".

      Note that this method returns a new Scheduler instance, even for the same Executor instance.

      It is possible to wrap an Executor into a Scheduler without triggering the initialization of all the standard schedulers by using the RxJavaPlugins.createExecutorScheduler(Executor, boolean, boolean) method before the Schedulers class itself is accessed.

      Parameters:
      executor - the executor to wrap
      Returns:
      the new Scheduler wrapping the Executor
      See Also:

    • from

      @NonNull public static @NonNull Scheduler from(@NonNull @NonNull Executor executor, boolean interruptibleWorker)
      Wraps an Executor into a new Scheduler instance and delegates schedule() calls to it.

      The tasks scheduled by the returned Scheduler and its Scheduler.Worker can be optionally interrupted.

      If the provided executor doesn't support any of the more specific standard Java executor APIs, tasks scheduled with a time delay or periodically will use the single() scheduler for the timed waiting before posting the actual task to the given executor.

      If the provided executor supports the standard Java ExecutorService API, tasks scheduled by this scheduler can be cancelled/interrupted by calling Disposable.dispose(). In addition, tasks scheduled with a time delay or periodically will use the single() scheduler for the timed waiting before posting the actual task to the given executor.

      If the provided executor supports the standard Java ScheduledExecutorService API, tasks scheduled by this scheduler can be cancelled/interrupted by calling Disposable.dispose(). In addition, tasks scheduled with a time delay or periodically will use the provided executor. Note, however, if the provided ScheduledExecutorService instance is not single threaded, tasks scheduled with a time delay close to each other may end up executing in different order than the original schedule() call was issued. This limitation may be lifted in a future patch.

      The implementation of the Worker of this wrapper Scheduler is eager and will execute as many non-delayed tasks as it can, which may result in a longer than expected occupation of a thread of the given backing Executor. In other terms, it does not allow per-Runnable fairness in case the worker runs on a shared underlying thread of the Executor. See from(Executor, boolean, boolean) to create a wrapper that uses the underlying Executor more fairly.

      Starting, stopping and restarting this scheduler is not supported (no-op) and the provided executor's lifecycle must be managed externally: 

      ExecutorService exec = Executors.newSingleThreadedExecutor();
try {
    Scheduler scheduler = Schedulers.from(exec, true);
    Flowable.just(1)
       .subscribeOn(scheduler)
       .map(v -> v + 1)
       .observeOn(scheduler)
       .blockingSubscribe(System.out::println);
} finally {
    exec.shutdown();
}

      Note that the provided Executor should avoid throwing a RejectedExecutionException (for example, by shutting it down prematurely or using a bounded-queue ExecutorService) because such circumstances prevent RxJava from progressing flow-related activities correctly. If the Executor.execute(Runnable) or ExecutorService.submit(Callable) throws, the RejectedExecutionException is routed to the global error handler via RxJavaPlugins.onError(Throwable). To avoid shutdown-related problems, it is recommended all flows using the returned Scheduler to be canceled/disposed before the underlying Executor is shut down. To avoid problems due to the Executor having a bounded-queue, it is recommended to rephrase the flow to utilize backpressure as the means to limit outstanding work.

      This type of scheduler is less sensitive to leaking Scheduler.Worker instances, although not disposing a worker that has timed/delayed tasks not cancelled by other means may leak resources and/or execute those tasks "unexpectedly".

      Note that this method returns a new Scheduler instance, even for the same Executor instance.

      It is possible to wrap an Executor into a Scheduler without triggering the initialization of all the standard schedulers by using the RxJavaPlugins.createExecutorScheduler(Executor, boolean, boolean) method before the Schedulers class itself is accessed.

      History: 2.2.6 - experimental

      Parameters:
      executor - the executor to wrap
      interruptibleWorker - if true, the tasks submitted to the Scheduler.Worker will be interrupted when the task is disposed.
      Returns:
      the new Scheduler wrapping the Executor
      Since:
      3.0.0
      See Also:

    • from

      @NonNull public static @NonNull Scheduler from(@NonNull @NonNull Executor executor, boolean interruptibleWorker, boolean fair)
      Wraps an Executor into a new Scheduler instance and delegates schedule() calls to it.

      The tasks scheduled by the returned Scheduler and its Scheduler.Worker can be optionally interrupted.

      If the provided executor doesn't support any of the more specific standard Java executor APIs, tasks scheduled with a time delay or periodically will use the single() scheduler for the timed waiting before posting the actual task to the given executor.

      If the provided executor supports the standard Java ExecutorService API, tasks scheduled by this scheduler can be cancelled/interrupted by calling Disposable.dispose(). In addition, tasks scheduled with a time delay or periodically will use the single() scheduler for the timed waiting before posting the actual task to the given executor.

      If the provided executor supports the standard Java ScheduledExecutorService API, tasks scheduled by this scheduler can be cancelled/interrupted by calling Disposable.dispose(). In addition, tasks scheduled with a time delay or periodically will use the provided executor. Note, however, if the provided ScheduledExecutorService instance is not single threaded, tasks scheduled with a time delay close to each other may end up executing in different order than the original schedule() call was issued. This limitation may be lifted in a future patch.

      The implementation of the Worker of this wrapper Scheduler can operate in both eager (non-fair) and fair modes depending on the specified parameter. In eager mode, it will execute as many non-delayed tasks as it can, which may result in a longer than expected occupation of a thread of the given backing Executor. In other terms, it does not allow per-Runnable fairness in case the worker runs on a shared underlying thread of the Executor. In fair mode, non-delayed tasks will still be executed in a FIFO and non-overlapping manner, but after each task, the execution for the next task is rescheduled with the same underlying Executor, allowing interleaving from both the same Scheduler or other external usages of the underlying Executor.

      Starting, stopping and restarting this scheduler is not supported (no-op) and the provided executor's lifecycle must be managed externally: 

      ExecutorService exec = Executors.newSingleThreadedExecutor();
try {
    Scheduler scheduler = Schedulers.from(exec, true, true);
    Flowable.just(1)
       .subscribeOn(scheduler)
       .map(v -> v + 1)
       .observeOn(scheduler)
       .blockingSubscribe(System.out::println);
} finally {
    exec.shutdown();
}

      Note that the provided Executor should avoid throwing a RejectedExecutionException (for example, by shutting it down prematurely or using a bounded-queue ExecutorService) because such circumstances prevent RxJava from progressing flow-related activities correctly. If the Executor.execute(Runnable) or ExecutorService.submit(Callable) throws, the RejectedExecutionException is routed to the global error handler via RxJavaPlugins.onError(Throwable). To avoid shutdown-related problems, it is recommended all flows using the returned Scheduler to be canceled/disposed before the underlying Executor is shut down. To avoid problems due to the Executor having a bounded-queue, it is recommended to rephrase the flow to utilize backpressure as the means to limit outstanding work.

      This type of scheduler is less sensitive to leaking Scheduler.Worker instances, although not disposing a worker that has timed/delayed tasks not cancelled by other means may leak resources and/or execute those tasks "unexpectedly".

      Note that this method returns a new Scheduler instance, even for the same Executor instance.

      It is possible to wrap an Executor into a Scheduler without triggering the initialization of all the standard schedulers by using the RxJavaPlugins.createExecutorScheduler(Executor, boolean, boolean) method before the Schedulers class itself is accessed.

      Parameters:
      executor - the executor to wrap
      interruptibleWorker - if true, the tasks submitted to the Scheduler.Worker will be interrupted when the task is disposed.
      fair - if true, tasks submitted to the Scheduler or Worker will be executed by the underlying Executor one after the other, still in a FIFO and non-overlapping manner, but allows interleaving with other tasks submitted to the underlying Executor. If false, the underlying FIFO scheme will execute as many tasks as it can before giving up the underlying Executor thread.
      Returns:
      the new Scheduler wrapping the Executor
      Since:
      3.0.0

    • shutdown

      public static void shutdown()
      Shuts down the standard Schedulers.

      The operation is idempotent and thread-safe.

    • start

      public static void start()
      Starts the standard Schedulers.

      The operation is idempotent and thread-safe.