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package org.boon.core.timer;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.locks.ReentrantLock;
/* This timer is used for caches and such
* It is a default timer.
* It should never be used direct.
* There should always be a fall back.
* By default this will reset the time every 100 times it is called to the latest
* System.nanoTime
* At most 1 thread will incur the cost of calling nanoTime about every 100 invocations.
*
*/
public class TimeKeeperBasic implements TimeKeeper {
private final AtomicInteger callEveryNowAndThen = new AtomicInteger();
private final AtomicLong time = new AtomicLong();
private final int TIME_KEEPER_FREQUENCY = Integer.parseInt( System.getProperty( "org.boon.timekeeper.frequency", "100" ) );
private final ReentrantLock lock = new ReentrantLock();
private final AtomicLong lastDeltaTime = new AtomicLong();
@Override
public final long time() {
long limit = callEveryNowAndThen.incrementAndGet();
long time;
boolean shouldGetTime = false;
if ( limit > TIME_KEEPER_FREQUENCY ) {
callEveryNowAndThen.set( 0 );
shouldGetTime = true;
}
/* Somewhat Ensure two calls to time do not return the exact same value. */
time = this.time.get() + limit;
if ( !shouldGetTime && ( limit % 20 == 0 ) ) {
checkForDrift( time );
}
return time;
}
/* Never let the drift get greater than 200 ms. */
private long checkForDrift( long time ) {
long delta = Math.abs( System.currentTimeMillis() - time );
long lastDelta = lastDeltaTime.getAndSet( delta );
if ( delta > lastDelta + 200 ) {
return getTheTime( time );
}
return time;
}
private long getTheTime( long time ) {
boolean locked = lock.tryLock(); //make sure two or more threads are not calling nanoTime.
if ( locked ) {
try {
//I don't want more than one thread calling nanoTime
time = System.nanoTime() / 1_000_000;
this.time.set( time );
return time;
} finally {
lock.unlock();
}
}
return time;
}
}