org.restcomm.media.concurrent.ConcurrentCyclicFIFO Maven / Gradle / Ivy
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* Copyright 2011, Red Hat, Inc. and individual contributors
* by the @authors tag. See the copyright.txt in the distribution for a
* full listing of individual contributors.
*
* This is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* This software is distributed in the hope that it will be useful,
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA, or see the FSF site: http://www.fsf.org.
*/
package org.restcomm.media.concurrent;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.ReentrantLock;
import java.util.concurrent.locks.Condition;
/**
* Modified copy of linked blocking queue currently goes to garbage - node
* elements which are based on 2 pointers : item and next and should signal
* boolean value under offer function
*
* @author oifa yulian
*/
public class ConcurrentCyclicFIFO {
static class Node {
volatile E item;
Node next;
Node(E x) {
item = x;
}
}
/** Current number of elements */
private final AtomicInteger count = new AtomicInteger(0);
/** Head of linked list */
private transient Node head;
/** Tail of linked list */
private transient Node last;
/** Lock held by take, poll, etc */
private final ReentrantLock takeLock = new ReentrantLock();
/** Wait queue for waiting takes */
private final Condition notEmpty = takeLock.newCondition();
/** Lock held by put, offer, etc */
private final ReentrantLock putLock = new ReentrantLock();
/**
* Signals a waiting take. Called only from put/offer (which do not
* otherwise ordinarily lock takeLock.)
*/
private void signalNotEmpty() {
final ReentrantLock takeLock = this.takeLock;
takeLock.lock();
try {
notEmpty.signal();
} finally {
takeLock.unlock();
}
}
/**
* Creates a node and links it at end of queue.
*
* @param x
* the item
*/
private void insert(Node x) {
last = last.next = x;
}
/**
* Removes a node from head of queue,
*
* @return the node
*/
private Node extract() {
Node current = head;
head = head.next;
current.item = head.item;
head.item = null;
return current;
}
public ConcurrentCyclicFIFO() {
last = head = new Node(null);
}
public int size() {
return count.get();
}
public boolean offer(E e) {
if (e == null) {
throw new NullPointerException();
}
final AtomicInteger count = this.count;
boolean shouldSignal = false;
final ReentrantLock putLock = this.putLock;
putLock.lock();
try {
insert(new Node(e));
shouldSignal = (count.getAndIncrement() == 0);
} finally {
putLock.unlock();
}
if (shouldSignal) {
signalNotEmpty();
}
return !shouldSignal;
}
public E take() throws InterruptedException {
Node x;
final AtomicInteger count = this.count;
final ReentrantLock takeLock = this.takeLock;
takeLock.lockInterruptibly();
try {
try {
while (count.get() == 0)
notEmpty.await();
} catch (InterruptedException ie) {
// propagate to a non-interrupted thread
notEmpty.signal();
throw ie;
}
x = extract();
if (count.getAndDecrement() > 1) {
notEmpty.signal();
}
} finally {
takeLock.unlock();
}
E result = x.item;
// temporary clearence
x.item = null;
x.next = null;
return result;
}
public E poll() {
final AtomicInteger count = this.count;
if (count.get() == 0) {
return null;
}
Node x = null;
final ReentrantLock takeLock = this.takeLock;
takeLock.lock();
try {
if (count.get() > 0) {
x = extract();
if (count.getAndDecrement() > 1) {
notEmpty.signal();
}
}
} finally {
takeLock.unlock();
}
if (x != null) {
E result = x.item;
// temporary clearence
x.item = null;
x.next = null;
return result;
}
return null;
}
public void clear() {
putLock.lock();
takeLock.lock();
try {
head.next = null;
assert head.item == null;
last = head;
count.set(0);
} finally {
takeLock.unlock();
putLock.unlock();
}
}
}