src/main/java/io/reactivex/plugins/RxJavaPlugins.java
@NonNull
    public static Runnable onSchedule(@NonNull Runnable run) {
        ObjectHelper.requireNonNull(run, "run is null");

        Function<? super Runnable, ? extends Runnable> f = onScheduleHandler;
        if (f == null) {
            return run;
        }
        return apply(f, run);
    }
@NonNull
    public static Runnable onSchedule(@NonNull Runnable run) {
        ObjectHelper.requireNonNull(run, "run is null");

        Function<? super Runnable, ? extends Runnable> f = onScheduleHandler;
        if (f == null) {
            return run;
        }
        return apply(f, run);
    }
@ NonNull public static Runnable onSchedule ( @ NonNull Runnable run ) { ObjectHelper . requireNonNull ( run , "run is null" ) ; Function < ? super Runnable , ? extends Runnable > f = onScheduleHandler ; if ( f == null ) { return run ; } return apply ( f , run ) ; }
Called when a task is scheduled.
@param run the runnable instance
@return the replacement runnable
Called when a task is scheduled .