com.hazelcast.cp.ICountDownLatch Maven / Gradle / Ivy
/*
* Copyright (c) 2008-2021, Hazelcast, Inc. All Rights Reserved.
*
* 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.hazelcast.cp;
import com.hazelcast.core.DistributedObject;
import java.util.concurrent.TimeUnit;
/**
* ICountDownLatch is a backed-up distributed alternative to the
* {@link java.util.concurrent.CountDownLatch java.util.concurrent.CountDownLatch}.
*
* ICountDownLatch is a cluster-wide synchronization aid
* that allows one or more threads to wait until a set of operations being
* performed in other threads completes.
*
* There are a few differences compared to the
* {@link java.util.concurrent.CountDownLatch java.util.concurrent.CountDownLatch}:
*
* -
* ICountDownLatch count can be reset using {@link #trySetCount(int)} after
* a countdown has finished but not during an active count. This allows
* the same latch instance to be reused.
*
* -
* There is no await() method to do an unbound wait since this is undesirable
* in a distributed application: for example, a cluster can split or the master
* and replicas could all die. In most cases, it is best to configure
* an explicit timeout so you have the ability to deal with these situations.
*
*
*
* {@link ICountDownLatch} is accessed via
* {@link CPSubsystem#getCountDownLatch(String)}. It works on top of the Raft
* consensus algorithm. It offers linearizability during crash failures and network
* partitions. It is CP with respect to the CAP principle. If a network
* partition occurs, it remains available on at most one side of the partition.
*
* All of the API methods in the new CP {@link ICountDownLatch} impl offer
* the exactly-once execution semantics. For instance, even if
* a {@link #countDown()} call is internally retried because of crashed
* Hazelcast member, the counter value is decremented only once.
*/
public interface ICountDownLatch extends DistributedObject {
/**
* Causes the current thread to wait until the latch has counted down to
* zero, or an exception is thrown, or the specified waiting time elapses.
*
* If the current count is zero then this method returns immediately
* with the value {@code true}.
*
* If the current count is greater than zero, then the current
* thread becomes disabled for thread scheduling purposes and lies
* dormant until one of five things happen:
*
* - the count reaches zero due to invocations of the
* {@link #countDown} method,
*
- this ICountDownLatch instance is destroyed,
*
- the countdown owner becomes disconnected,
*
- some other thread {@linkplain Thread#interrupt interrupts}
* the current thread, or
*
- the specified waiting time elapses.
*
* If the count reaches zero, then the method returns with the
* value {@code true}.
*
* If the current thread:
*
* - has its interrupted status set on entry to this method, or
*
- is {@linkplain Thread#interrupt interrupted} while waiting,
*
* then {@link InterruptedException} is thrown and the current thread's
* interrupted status is cleared.
*
* If the specified waiting time elapses then the value {@code false}
* is returned. If the time is less than or equal to zero, the method
* will not wait at all.
*
* @param timeout the maximum time to wait
* @param unit the time unit of the {@code timeout} argument
* @return {@code true} if the count reached zero, {@code false}
* if the waiting time elapsed before the count reached zero
* @throws InterruptedException if the current thread is interrupted
* @throws IllegalStateException if the Hazelcast instance is shutdown while waiting
* @throws NullPointerException if unit is null
*/
boolean await(long timeout, TimeUnit unit) throws InterruptedException;
/**
* Decrements the count of the latch, releasing all waiting threads if
* the count reaches zero.
*
* If the current count is greater than zero, then it is decremented.
* If the new count is zero:
*
* - All waiting threads are re-enabled for thread scheduling purposes, and
*
- Countdown owner is set to {@code null}.
*
* If the current count equals zero, then nothing happens.
*/
void countDown();
/**
* Returns the current count.
*
* @return the current count
*/
int getCount();
/**
* Sets the count to the given value if the current count is zero.
*
* If count is not zero, then this method does nothing and returns {@code false}.
*
* @param count the number of times {@link #countDown} must be invoked
* before threads can pass through {@link #await}
* @return {@code true} if the new count was set, {@code false} if the current count is not zero
* @throws IllegalArgumentException if {@code count} is negative or zero
*/
boolean trySetCount(int count);
}