panda.task.PeriodicTrigger Maven / Gradle / Ivy
package panda.task;
import panda.lang.Asserts;
import java.util.Date;
import java.util.concurrent.TimeUnit;
/**
* A trigger for periodic task execution. The period may be applied as either
* fixed-rate or fixed-delay, and an initial delay value may also be configured.
* The default initial delay is 0, and the default behavior is fixed-delay
* (i.e. the interval between successive executions is measured from each
* completion time). To measure the interval between the
* scheduled start time of each execution instead, set the
* 'fixedRate' property to {@code true}.
*
* Note that the TaskScheduler interface already defines methods for scheduling
* tasks at fixed-rate or with fixed-delay. Both also support an optional value
* for the initial delay. Those methods should be used directly whenever
* possible. The value of this Trigger implementation is that it can be used
* within components that rely on the Trigger abstraction. For example, it may
* be convenient to allow periodic triggers, cron-based triggers, and even
* custom Trigger implementations to be used interchangeably.
*/
public class PeriodicTrigger implements Trigger {
private final long period;
private final TimeUnit timeUnit;
private volatile long initialDelay = 0;
private volatile boolean fixedRate = false;
/**
* Create a trigger with the given period in milliseconds.
*
* @param period the period
*/
public PeriodicTrigger(long period) {
this(period, null);
}
/**
* Create a trigger with the given period and time unit. The time unit will
* apply not only to the period but also to any 'initialDelay' value, if
* configured on this Trigger later via {@link #setInitialDelay(long)}.
*
* @param period the period
* @param timeUnit the time unit
*/
public PeriodicTrigger(long period, TimeUnit timeUnit) {
Asserts.isTrue(period >= 0, "period must not be negative");
this.timeUnit = (timeUnit != null ? timeUnit : TimeUnit.MILLISECONDS);
this.period = this.timeUnit.toMillis(period);
}
/**
* Specify the delay for the initial execution. It will be evaluated in
* terms of this trigger's {@link TimeUnit}. If no time unit was explicitly
* provided upon instantiation, the default is milliseconds.
*
* @param initialDelay the initial delay
*/
public void setInitialDelay(long initialDelay) {
this.initialDelay = this.timeUnit.toMillis(initialDelay);
}
/**
* Specify whether the periodic interval should be measured between the
* scheduled start times rather than between actual completion times.
* The latter, "fixed delay" behavior, is the default.
*
* @param fixedRate the fixed rate
*/
public void setFixedRate(boolean fixedRate) {
this.fixedRate = fixedRate;
}
/**
* Returns the time after which a task should run again.
*/
@Override
public Date nextExecutionTime(TriggerContext triggerContext) {
if (triggerContext.lastScheduledExecutionTime() == null) {
return new Date(System.currentTimeMillis() + this.initialDelay);
}
else if (this.fixedRate) {
return new Date(triggerContext.lastScheduledExecutionTime().getTime() + this.period);
}
return new Date(triggerContext.lastCompletionTime().getTime() + this.period);
}
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (!(obj instanceof PeriodicTrigger)) {
return false;
}
PeriodicTrigger other = (PeriodicTrigger) obj;
return (this.fixedRate == other.fixedRate && this.initialDelay == other.initialDelay && this.period == other.period);
}
@Override
public int hashCode() {
return (this.fixedRate ? 17 : 29) + (int) (37 * this.period) + (int) (41 * this.initialDelay);
}
}