CountDownCompleter.java
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/*
* Copyright 2016-present Open Networking Laboratory
*
* 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 org.onlab.util;
import java.util.concurrent.atomic.AtomicLong;
import java.util.function.Consumer;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
/**
* A synchronization utility that defers invocation of a {@link Consumer consumer}
* callback until a set number of actions tracked by a {@code long} counter complete.
* <p>
* Each completion is recorded by invoking the {@link CountDownCompleter#countDown countDown}
* method. When the total number of completions is equal to the preset counter value,
* this instance is marked as completed and the callback invoked by supplying the object
* held by this instance.
*
* @param <T> object type
*/
public final class CountDownCompleter<T> {
private final T object;
private final Consumer<T> onCompleteCallback;
private final AtomicLong counter;
/**
* Constructor.
* @param object object
* @param count total number of times countDown must be invoked for this completer to complete
* @param onCompleteCallback callback to invoke when completer is completed
*/
public CountDownCompleter(T object, long count, Consumer<T> onCompleteCallback) {
checkState(count >= 0, "count must be non-negative");
this.counter = new AtomicLong(count);
this.object = checkNotNull(object);
this.onCompleteCallback = checkNotNull(onCompleteCallback);
if (count == 0) {
onCompleteCallback.accept(object);
}
}
/**
* Returns the object.
* @return object
*/
public T object() {
return object;
}
/**
* Records a single completion.
* <p>
* If this instance has already completed, this method has no effect
*/
public void countDown() {
if (counter.decrementAndGet() == 0) {
onCompleteCallback.accept(object);
}
}
/**
* Returns if this instance has completed.
* @return {@code true} if completed
*/
public boolean isComplete() {
return counter.get() <= 0;
}
}