/*
* Copyright 2002-2016 the original author or authors.
*
* 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.springframework.integration.util;
import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;
/**
* Thin wrapper around a Semaphore that allows to create a potentially unlimited upper bound
* to by used in buffers of messages (e.g. a QueueChannel or a MessageStore).
*
* @author Mark Fisher
* @author Iwein Fuld
* @author Artem Bilan
*
* @since 2.0
*/
public final class UpperBound {
public final Semaphore semaphore;
/**
* Create an UpperBound with the given capacity. If the given capacity is less than 1
* an infinite UpperBound is created.
*
* @param capacity The capacity.
*/
public UpperBound(int capacity) {
this.semaphore = (capacity > 0) ? new Semaphore(capacity, true) : null;
}
public int availablePermits() {
if (this.semaphore == null) {
return Integer.MAX_VALUE;
}
return this.semaphore.availablePermits();
}
/**
* Acquires a permit from the underlying semaphore if this UpperBound is bounded and returns
* true if it succeeds within the given timeout. If the timeout is less than 0, it will block
* indefinitely.
*
* @param timeoutInMilliseconds The time to wait until a permit is available.
* @return true if a permit is acquired.
*/
public boolean tryAcquire(long timeoutInMilliseconds) {
if (this.semaphore != null) {
try {
if (timeoutInMilliseconds < 0) {
this.semaphore.acquire();
return true;
}
return this.semaphore.tryAcquire(timeoutInMilliseconds, TimeUnit.MILLISECONDS);
}
catch (InterruptedException e) {
Thread.currentThread().interrupt();
return false;
}
}
return true;
}
/**
* Releases one lock on the underlying semaphore. This is typically not done by the same Thread
* that acquired the lock, but by the thread that picked up the message.
*/
public void release() {
if (this.semaphore != null) {
this.semaphore.release();
}
}
/**
* Releases several locks on the underlying semaphore. This is typically not done by the same Thread
* that acquired the lock, but by the thread that picked up the message.
*
* @param permits The number of permits to release.
*/
public void release(int permits) {
if (this.semaphore != null) {
this.semaphore.release(permits);
}
}
@Override
public String toString() {
return super.toString() + "[Permits = " +
(this.semaphore != null ? this.semaphore.availablePermits() : "UNLIMITED") + "]";
}
}