rx.internal.schedulers.SchedulePeriodicHelper Maven / Gradle / Ivy
/**
* Copyright 2016 Netflix, Inc.
*
* 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 rx.internal.schedulers;
import java.util.concurrent.TimeUnit;
import rx.Scheduler.Worker;
import rx.Subscription;
import rx.functions.Action0;
import rx.internal.subscriptions.SequentialSubscription;
/**
* Utility method for scheduling tasks periodically (at a fixed rate) by using Worker.schedule(Action0, long, TimeUnit).
*/
public final class SchedulePeriodicHelper {
/** Utility class. */
private SchedulePeriodicHelper() {
throw new IllegalStateException("No instances!");
}
/**
* The tolerance for a clock drift in nanoseconds where the periodic scheduler will rebase.
*
* The associated system parameter, {@code rx.scheduler.drift-tolerance}, expects its value in minutes.
*/
public static final long CLOCK_DRIFT_TOLERANCE_NANOS;
static {
CLOCK_DRIFT_TOLERANCE_NANOS = TimeUnit.MINUTES.toNanos(
Long.getLong("rx.scheduler.drift-tolerance", 15));
}
/**
* Return the current time in nanoseconds.
*/
public interface NowNanoSupplier {
long nowNanos();
}
public static Subscription schedulePeriodically(
final Worker worker,
final Action0 action,
long initialDelay, long period, TimeUnit unit,
final NowNanoSupplier nowNanoSupplier) {
final long periodInNanos = unit.toNanos(period);
final long firstNowNanos = nowNanoSupplier != null ? nowNanoSupplier.nowNanos() : TimeUnit.MILLISECONDS.toNanos(worker.now());
final long firstStartInNanos = firstNowNanos + unit.toNanos(initialDelay);
final SequentialSubscription first = new SequentialSubscription();
final SequentialSubscription mas = new SequentialSubscription(first);
final Action0 recursiveAction = new Action0() {
long count;
long lastNowNanos = firstNowNanos;
long startInNanos = firstStartInNanos;
@Override
public void call() {
action.call();
if (!mas.isUnsubscribed()) {
long nextTick;
long nowNanos = nowNanoSupplier != null ? nowNanoSupplier.nowNanos() : TimeUnit.MILLISECONDS.toNanos(worker.now());
// If the clock moved in a direction quite a bit, rebase the repetition period
if (nowNanos + CLOCK_DRIFT_TOLERANCE_NANOS < lastNowNanos
|| nowNanos >= lastNowNanos + periodInNanos + CLOCK_DRIFT_TOLERANCE_NANOS) {
nextTick = nowNanos + periodInNanos;
/*
* Shift the start point back by the drift as if the whole thing
* started count periods ago.
*/
startInNanos = nextTick - (periodInNanos * (++count));
} else {
nextTick = startInNanos + (++count * periodInNanos);
}
lastNowNanos = nowNanos;
long delay = nextTick - nowNanos;
mas.replace(worker.schedule(this, delay, TimeUnit.NANOSECONDS));
}
}
};
first.replace(worker.schedule(recursiveAction, initialDelay, unit));
return mas;
}
}