com.codahale.metrics.CachedGauge Maven / Gradle / Ivy
package com.codahale.metrics;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;
/**
* A {@link Gauge} implementation which caches its value for a period of time.
*
* @param the type of the gauge's value
*/
public abstract class CachedGauge implements Gauge {
private final Clock clock;
private final AtomicLong reloadAt;
private final long timeoutNS;
private volatile T value;
/**
* Creates a new cached gauge with the given timeout period.
*
* @param timeout the timeout
* @param timeoutUnit the unit of {@code timeout}
*/
protected CachedGauge(long timeout, TimeUnit timeoutUnit) {
this(Clock.defaultClock(), timeout, timeoutUnit);
}
/**
* Creates a new cached gauge with the given clock and timeout period.
*
* @param clock the clock used to calculate the timeout
* @param timeout the timeout
* @param timeoutUnit the unit of {@code timeout}
*/
protected CachedGauge(Clock clock, long timeout, TimeUnit timeoutUnit) {
this.clock = clock;
this.reloadAt = new AtomicLong(0);
this.timeoutNS = timeoutUnit.toNanos(timeout);
}
/**
* Loads the value and returns it.
*
* @return the new value
*/
protected abstract T loadValue();
@Override
public T getValue() {
if (shouldLoad()) {
this.value = loadValue();
}
return value;
}
private boolean shouldLoad() {
for (; ; ) {
final long time = clock.getTick();
final long current = reloadAt.get();
if (current > time) {
return false;
}
if (reloadAt.compareAndSet(current, time + timeoutNS)) {
return true;
}
}
}
}