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/*
*
* Copyright (c) 2006 The Apache Software Foundation
*
* 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.apache.qpid.client.util;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;
/**
* A blocking queue that emits events above a user specified threshold allowing
* the caller to take action (e.g. flow control) to try to prevent the queue
* growing (much) further. The underlying queue itself is not bounded therefore
* the caller is not obliged to react to the events.
* <p/>
* This implementation is <b>only</b> safe where we have a single thread adding
* items and a single (different) thread removing items.
*/
public class FlowControllingBlockingQueue
{
/**
* This queue is bounded and is used to store messages before being dispatched to the consumer
*/
private final BlockingQueue _queue = new LinkedBlockingQueue();
private final int _flowControlHighThreshold;
private final int _flowControlLowThreshold;
private final ThresholdListener _listener;
/**
* We require a separate count so we can track whether we have reached the
* threshold
*/
private int _count;
public interface ThresholdListener
{
void aboveThreshold(int currentValue);
void underThreshold(int currentValue);
}
public FlowControllingBlockingQueue(int threshold, ThresholdListener listener)
{
this(threshold, threshold, listener);
}
public FlowControllingBlockingQueue(int highThreshold, int lowThreshold, ThresholdListener listener)
{
_flowControlHighThreshold = highThreshold;
_flowControlLowThreshold = lowThreshold;
_listener = listener;
}
public Object take() throws InterruptedException
{
Object o = _queue.take();
if (_listener != null)
{
synchronized(_listener)
{
if (_count-- == _flowControlLowThreshold)
{
_listener.underThreshold(_count);
}
}
}
return o;
}
public void add(Object o)
{
_queue.add(o);
if (_listener != null)
{
synchronized(_listener)
{
if (++_count == _flowControlHighThreshold)
{
_listener.aboveThreshold(_count);
}
}
}
}
}
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