非阻塞算法
以下内容摘自 http://www.ibm.com/developerworks/java/library/j-jtp04186/index.html?S_TACT=105AGX02&S_CMP=EDU1. 使用CAS的非阻塞计数器
public class NonblockingCounter { private AtomicInteger value; public int getValue() { return value.get(); } public int increment() { int v; do { v = value.get(); } while (!value.compareAndSet(v, v + 1)); return v + 1; }}
2. 使用Treiber算法的非阻塞栈
public class ConcurrentStack<E> { AtomicReference<Node<E>> head = new AtomicReference<Node<E>>(); public void push(E item) { Node<E> newHead = new Node<E>(item); Node<E> oldHead; do { oldHead = head.get(); newHead.next = oldHead; } while (!head.compareAndSet(oldHead, newHead)); } public E pop() { Node<E> oldHead; Node<E> newHead; do { oldHead = head.get(); if (oldHead == null) return null; newHead = oldHead.next; } while (!head.compareAndSet(oldHead,newHead)); return oldHead.item; } static class Node<E> { final E item; Node<E> next; public Node(E item) { this.item = item; } }}
3. Michael-Scott的非阻塞队列算法
public class LinkedQueue <E> { private static class Node <E> { final E item; final AtomicReference<Node<E>> next; Node(E item, Node<E> next) { this.item = item; this.next = new AtomicReference<Node<E>>(next); } } private AtomicReference<Node<E>> head = new AtomicReference<Node<E>>(new Node<E>(null, null)); private AtomicReference<Node<E>> tail = head; public boolean put(E item) { Node<E> newNode = new Node<E>(item, null); while (true) { Node<E> curTail = tail.get(); Node<E> residue = curTail.next.get(); if (curTail == tail.get()) { if (residue == null) /* A */ { if (curTail.next.compareAndSet(null, newNode)) /* C */ { tail.compareAndSet(curTail, newNode) /* D */ ; return true; } } else { tail.compareAndSet(curTail, residue) /* B */; } } } }}
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