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/*
* 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.alipay.disruptor;
import java.util.concurrent.TimeUnit;
/**
* Phased wait strategy for waiting {@link EventProcessor}s on a barrier.
*
* This strategy can be used when throughput and low-latency are not as important as CPU resource.
* Spins, then yields, then waits using the configured fallback WaitStrategy.
*/
public final class PhasedBackoffWaitStrategy implements WaitStrategy {
private static final int SPIN_TRIES = 10000;
private final long spinTimeoutNanos;
private final long yieldTimeoutNanos;
private final WaitStrategy fallbackStrategy;
public PhasedBackoffWaitStrategy(long spinTimeout, long yieldTimeout, TimeUnit units,
WaitStrategy fallbackStrategy) {
this.spinTimeoutNanos = units.toNanos(spinTimeout);
this.yieldTimeoutNanos = spinTimeoutNanos + units.toNanos(yieldTimeout);
this.fallbackStrategy = fallbackStrategy;
}
/**
* Block with wait/notifyAll semantics
* @param spinTimeout spinTimeout
* @param yieldTimeout yieldTimeout
* @param units units
* @return PhasedBackoffWaitStrategy
*/
public static PhasedBackoffWaitStrategy withLock(long spinTimeout, long yieldTimeout,
TimeUnit units) {
return new PhasedBackoffWaitStrategy(spinTimeout, yieldTimeout, units,
new BlockingWaitStrategy());
}
/**
* Block with wait/notifyAll semantics
* @param spinTimeout spinTimeout
* @param yieldTimeout yieldTimeout
* @param units units
* @return PhasedBackoffWaitStrategy
*/
public static PhasedBackoffWaitStrategy withLiteLock(long spinTimeout, long yieldTimeout,
TimeUnit units) {
return new PhasedBackoffWaitStrategy(spinTimeout, yieldTimeout, units,
new LiteBlockingWaitStrategy());
}
/**
* Block by sleeping in a loop
* @param spinTimeout spinTimeout
* @param yieldTimeout yieldTimeout
* @param units units
* @return PhasedBackoffWaitStrategy
*/
public static PhasedBackoffWaitStrategy withSleep(long spinTimeout, long yieldTimeout,
TimeUnit units) {
return new PhasedBackoffWaitStrategy(spinTimeout, yieldTimeout, units,
new SleepingWaitStrategy(0));
}
@Override
public long waitFor(long sequence, Sequence cursor, Sequence dependentSequence,
SequenceBarrier barrier) throws AlertException, InterruptedException,
TimeoutException {
long availableSequence;
long startTime = 0;
int counter = SPIN_TRIES;
do {
if ((availableSequence = dependentSequence.get()) >= sequence) {
return availableSequence;
}
if (0 == --counter) {
if (0 == startTime) {
startTime = System.nanoTime();
} else {
long timeDelta = System.nanoTime() - startTime;
if (timeDelta > yieldTimeoutNanos) {
return fallbackStrategy.waitFor(sequence, cursor, dependentSequence,
barrier);
} else if (timeDelta > spinTimeoutNanos) {
Thread.yield();
}
}
counter = SPIN_TRIES;
}
} while (true);
}
@Override
public void signalAllWhenBlocking() {
fallbackStrategy.signalAllWhenBlocking();
}
}