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JQF: Feedback-directed Quickcheck for Java - Instrumentation and event generation module
/*
* Copyright (c) 2017-2018 The Regents of the University of California
*
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package edu.berkeley.cs.jqf.instrument.util;
/**
* A blocking queue for single-producer and single-consumer where the producer and
* consumer never change and are distinct threads.
*
* This allows reading and writing from the queue without using system
* locks. The only synchronization is via volatile pointers for the producer
* and consumer in a fixed-size circular buffer.
*
* Reading from an empty queue and writing to a full queue results in a spinning wait,
* and therefore the producer and consumer must be distinct in order to avoid
* deadlocks.
*
* @author Rohan Padhye
*/
public final class FastBlockingQueue {
private final int size;
private final Object[] buffer;
private volatile int producer = 0;
private volatile int consumer = 0;
public FastBlockingQueue(int size) {
this.size = size;
this.buffer = new Object[size];
}
private int increment(int idx) {
return (idx + 1) % size;
}
public final boolean isEmpty() {
return producer == consumer;
}
public final boolean isFull() {
return increment(producer) == consumer;
}
public final void put(T item) {
while (isFull()) {
// Spin-block
}
buffer[producer] = item;
producer = increment(producer);
}
public final T remove(long timeout) {
long ticks = 0;
while(isEmpty()) {
if (++ticks > timeout) {
return null;
}
}
@SuppressWarnings("unchecked")
T item = (T) buffer[consumer];
consumer = increment(consumer);
return item;
}
}