com.alipay.disruptor.LiteBlockingWaitStrategy Maven / Gradle / Ivy

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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.atomic.AtomicBoolean;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * Variation of the {@link BlockingWaitStrategy} that attempts to elide conditional wake-ups when
 * the lock is uncontended.  Shows performance improvements on microbenchmarks.  However this
 * wait strategy should be considered experimental as I have not full proved the correctness of
 * the lock elision code.
 */
public final class LiteBlockingWaitStrategy implements WaitStrategy {
    private final Lock          lock                     = new ReentrantLock();
    private final Condition     processorNotifyCondition = lock.newCondition();
    private final AtomicBoolean signalNeeded             = new AtomicBoolean(false);

    @Override
    public long waitFor(long sequence, Sequence cursorSequence, Sequence dependentSequence,
                        SequenceBarrier barrier) throws AlertException, InterruptedException {
        long availableSequence;
        if (cursorSequence.get() < sequence) {
            lock.lock();

            try {
                do {
                    signalNeeded.getAndSet(true);

                    if (cursorSequence.get() >= sequence) {
                        break;
                    }

                    barrier.checkAlert();
                    processorNotifyCondition.await();
                } while (cursorSequence.get() < sequence);
            } finally {
                lock.unlock();
            }
        }

        while ((availableSequence = dependentSequence.get()) < sequence) {
            barrier.checkAlert();
        }

        return availableSequence;
    }

    @Override
    public void signalAllWhenBlocking() {
        if (signalNeeded.getAndSet(false)) {
            lock.lock();
            try {
                processorNotifyCondition.signalAll();
            } finally {
                lock.unlock();
            }
        }
    }

    @Override
    public String toString() {
        return "LiteBlockingWaitStrategy{" + "processorNotifyCondition=" + processorNotifyCondition
               + '}';
    }
}