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POIs this (Lock-Free) Queue Implementation Thread-Safe?
 

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    <p>I am trying to create a lock-free queue implementation in Java, mainly for personal learning. The queue should be a general one, allowing any number of readers and/or writers concurrently.</p> <p>Would you please review it, and suggest any improvements/issues you find?</p> <p>Thank you.</p> <pre><code>import java.util.concurrent.atomic.AtomicReference; public class LockFreeQueue&lt;T&gt; { private static class Node&lt;E&gt; { E value; volatile Node&lt;E&gt; next; Node(E value) { this.value = value; } } private AtomicReference&lt;Node&lt;T&gt;&gt; head, tail; public LockFreeQueue() { // have both head and tail point to a dummy node Node&lt;T&gt; dummyNode = new Node&lt;T&gt;(null); head = new AtomicReference&lt;Node&lt;T&gt;&gt;(dummyNode); tail = new AtomicReference&lt;Node&lt;T&gt;&gt;(dummyNode); } /** * Puts an object at the end of the queue. */ public void putObject(T value) { Node&lt;T&gt; newNode = new Node&lt;T&gt;(value); Node&lt;T&gt; prevTailNode = tail.getAndSet(newNode); prevTailNode.next = newNode; } /** * Gets an object from the beginning of the queue. The object is removed * from the queue. If there are no objects in the queue, returns null. */ public T getObject() { Node&lt;T&gt; headNode, valueNode; // move head node to the next node using atomic semantics // as long as next node is not null do { headNode = head.get(); valueNode = headNode.next; // try until the whole loop executes pseudo-atomically // (i.e. unaffected by modifications done by other threads) } while (valueNode != null &amp;&amp; !head.compareAndSet(headNode, valueNode)); T value = (valueNode != null ? valueNode.value : null); // release the value pointed to by head, keeping the head node dummy if (valueNode != null) valueNode.value = null; return value; } </code></pre>
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    1. COPorted to Code Review at http://codereview.stackexchange.com/questions/224/is-this-lock-free-queue-implementation-thread-safe
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