/*
* Copyright (c) 2008-2012, Hazel Bilisim Ltd. 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.core;
import com.hazelcast.monitor.LocalCountDownLatchStats;
import java.util.concurrent.TimeUnit;
/**
* ICountDownLatch is a backed-up distributed implementation of
* {@link java.util.concurrent.CountDownLatch java.util.concurrent.CountDownLatch}.
* <p/>
* Hazelcast's 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.
* <p/>
* Unlike Java's implementation, Hazelcast's ICountDownLatch count can be re-set
* after a countdown has finished but not during an active count. This allows the same
* proxy instance to be reused.
* <p/>The Hazelcast member that successfully invokes {@link #setCount(int)} becomes
* the owner of the countdown and is responsible for staying connected to
* the cluster until the count reaches zero. If the owner becomes disconnected prior
* to count reaching zero all awaiting threads will be notified. This provides a
* safety mechanism in the distributed environment.
*/
public interface ICountDownLatch extends Instance {
/**
* Returns the name of this ICountDownLatch instance.
*
* @return name of this instance
*/
String getName();
/**
* Causes the current thread to wait until the latch has counted down to
* zero or an exception is thrown.
* <p/>
* <p>If the current count is zero then this method returns immediately.
* <p/>
* <p>If the current count is greater than zero then the current
* thread becomes disabled for thread scheduling purposes and lies
* dormant until one of four things happen:
* <ul>
* <li>The count reaches zero due to invocations of the
* {@link #countDown} method;
* <li>This ICountDownLatch instance is destroyed;
* <li>The countdown owner becomes disconnected; or
* <li>Some other thread {@linkplain Thread#interrupt interrupts}
* the current thread.
* </ul>
* <p/>If the ICountDownLatch instance is destroyed while waiting then
* {@link InstanceDestroyedException} will be thrown.
* <p/>If the countdown owner becomes disconnected while waiting then
* {@link MemberLeftException} will be thrown.
* <p>If the current thread:
* <ul>
* <li>has its interrupted status set on entry to this method; or
* <li>is {@linkplain Thread#interrupt interrupted} while waiting,
* </ul>
* then {@link InterruptedException} is thrown and the current thread's
* interrupted status is cleared.
*
* @throws InstanceDestroyedException if the instance is destroyed while waiting
* @throws MemberLeftException if the countdown owner becomes disconnected while waiting
* @throws InterruptedException if the current thread is interrupted
* @throws IllegalStateException if hazelcast instance is shutdown while waiting
*/
public void await() throws InstanceDestroyedException, MemberLeftException, InterruptedException;
/**
* Causes the current thread to wait until the latch has counted down to
* zero, an exception is thrown, or the specified waiting time elapses.
* <p/>
* <p>If the current count is zero then this method returns immediately
* with the value {@code true}.
* <p/>
* <p>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:
* <ul>
* <li>The count reaches zero due to invocations of the
* {@link #countDown} method;
* <li>This ICountDownLatch instance is destroyed;
* <li>The countdown owner becomes disconnected;
* <li>Some other thread {@linkplain Thread#interrupt interrupts}
* the current thread; or
* <li>The specified waiting time elapses.
* </ul>
* <p/>
* <p>If the count reaches zero then the method returns with the
* value {@code true}.
* <p/>
* <p/>If the ICountDownLatch instance is destroyed while waiting then
* {@link InstanceDestroyedException} will be thrown.
* <p/>If the countdown owner becomes disconnected while waiting then
* {@link MemberLeftException} will be thrown.
* <p>If the current thread:
* <ul>
* <li>has its interrupted status set on entry to this method; or
* <li>is {@linkplain Thread#interrupt interrupted} while waiting,
* </ul>
* then {@link InterruptedException} is thrown and the current thread's
* interrupted status is cleared.
* <p>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 and {@code false}
* if the waiting time elapsed before the count reached zero
* @throws InstanceDestroyedException if the instance is destroyed while waiting
* @throws MemberLeftException if the countdown owner becomes disconnected while waiting
* @throws InterruptedException if the current thread is interrupted
* @throws IllegalStateException if hazelcast instance is shutdown while waiting
*/
public boolean await(long timeout, TimeUnit unit) throws InstanceDestroyedException, MemberLeftException, InterruptedException;
/**
* Decrements the count of the latch, releasing all waiting threads if
* the count reaches zero.
* <p/>
* If the current count is greater than zero then it is decremented.
* If the new count is zero:
* <ul>
* <li>All waiting threads are re-enabled for thread scheduling purposes; and
* <li>Countdown owner is set to {@code null}.
* </ul>
* <p/>
* If the current count equals zero then nothing happens.
*/
public void countDown();
/**
* Returns whether the current count is greater than zero.
*
* @return {@code true} if count is greater than zero
*/
public boolean hasCount();
/**
* Sets the count to the given value if the current count is zero. The calling
* cluster member becomes the owner of the countdown and is responsible for
* staying connected to the cluster until the count reaches zero.
* <p/>If the owner becomes disconnected before the count reaches zero:
* <ul>
* <li>Count will be set to zero;
* <li>Countdown owner will be set to {@code null}; and
* <li>All awaiting threads will be thrown a {@link MemberLeftException}.
* </ul>
* <p/>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 or {@code false} if the current
* count is not zero
* @throws IllegalArgumentException if {@code count} is negative
*/
public boolean setCount(int count);
LocalCountDownLatchStats getLocalCountDownLatchStats();
}