/*
* Copyright 2011 LMAX Ltd.
*
* 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 com.lmax.disruptor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.LockSupport;
import static com.lmax.disruptor.util.Util.getMinimumSequence;
/**
* Sleeping strategy that initially spins, then uses a Thread.yield(), and eventually for the minimum number of nanos
* the OS and JVM will allow while the {@link com.lmax.disruptor.EventProcessor}s are waiting on a barrier.
*
* This strategy is a good compromise between performance and CPU resource. Latency spikes can occur after quiet periods.
*/
public final class SleepingWaitStrategy implements WaitStrategy
{
private static final int RETRIES = 200;
@Override
public long waitFor(final long sequence, final Sequence cursor, final Sequence[] dependents, final SequenceBarrier barrier)
throws AlertException, InterruptedException
{
long availableSequence;
int counter = RETRIES;
if (0 == dependents.length)
{
while ((availableSequence = cursor.get()) < sequence)
{
counter = applyWaitMethod(barrier, counter);
}
}
else
{
while ((availableSequence = getMinimumSequence(dependents)) < sequence)
{
counter = applyWaitMethod(barrier, counter);
}
}
return availableSequence;
}
@Override
public long waitFor(final long sequence, final Sequence cursor, final Sequence[] dependents, final SequenceBarrier barrier,
final long timeout, final TimeUnit sourceUnit)
throws AlertException, InterruptedException
{
final long timeoutMs = sourceUnit.toMillis(timeout);
final long startTime = System.currentTimeMillis();
long availableSequence;
int counter = RETRIES;
if (0 == dependents.length)
{
while ((availableSequence = cursor.get()) < sequence)
{
counter = applyWaitMethod(barrier, counter);
final long elapsedTime = System.currentTimeMillis() - startTime;
if (elapsedTime > timeoutMs)
{
break;
}
}
}
else
{
while ((availableSequence = getMinimumSequence(dependents)) < sequence)
{
counter = applyWaitMethod(barrier, counter);
final long elapsedTime = System.currentTimeMillis() - startTime;
if (elapsedTime > timeoutMs)
{
break;
}
}
}
return availableSequence;
}
@Override
public void signalAllWhenBlocking()
{
}
private int applyWaitMethod(final SequenceBarrier barrier, int counter)
throws AlertException
{
barrier.checkAlert();
if (counter > 100)
{
--counter;
}
else if (counter > 0)
{
--counter;
Thread.yield();
}
else
{
LockSupport.parkNanos(1L);
}
return counter;
}
}