java.util.concurrent.atomic.*包的体会
java.util.concurrent.atomic.*包的体会
package thread.concurrent.atomic;import java.util.HashMap;import java.util.Map;import java.util.Random;import java.util.concurrent.atomic.AtomicLong;import java.util.concurrent.atomic.AtomicReference;import sun.misc.Unsafe;public class AtomicTest {AtomicLong atomicLong = new AtomicLong(11);AtomicReference<Map> atomicRef = null;// private static long value = 10;// private static final Unsafe unsafe = Unsafe.getUnsafe();public static void main(String[] args) throws SecurityException,NoSuchFieldException {final AtomicTest atomicLongTest = new AtomicTest();atomicLongTest.set();for (int i = 0; i < 10; i++) {new Thread() {public void run() {atomicLongTest.updateRef();};}.start();}// Field valueField = AtomicLongTest.class.getDeclaredField("value");// long ll = unsafe.objectFieldOffset(valueField);// System.out.println(ll);}private void set() {Map map = new HashMap();map.put("name", "name1");//通过AtomicReference封装的对象就是原子对象了。atomicRef = new AtomicReference<Map>(map);}private Object updateRef() {boolean f;Map expect;do {expect = atomicRef.get();Map update = new HashMap();update.putAll(expect);int n = (new Random()).nextInt(1000);update.put("name", n);try {Thread.sleep(100);} catch (InterruptedException e) {e.printStackTrace();}f = atomicRef.compareAndSet(expect, update);System.out.println(Thread.currentThread().getName() + ",得到的原来的map:"+ expect + ",新的map:" + update + ",f:" + f);} while (!f);return expect;}private long count() {boolean f;long r;try {Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}do {r = atomicLong.get();try {Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}/** * AtomicLong这个类是提供原子操作的帮助类，其实没多少实质性的内容，这个类主要靠compareAndSet这个方， * 而这个方法其实是调用sun.misc.Unsafe这个非安全类完成的。之所以说是非安全类是因为这个类会根据平台的不同调用 * 当前平台的本地API做事,这个包也是SUN唯一没有公开的包。 首先回去得到一个Unsafe unsafe = * Unsafe.getUnsafe();的对象 * 然后调用unsafe.compareAndSwapLong(this,valueOffset, expect, * update);方法完成任务的。 * * 把value申明成volatile的，其他的方法可以随便写了。 * */f = atomicLong.compareAndSet(r, r + 1);// 比较并且更新值，如果更新失败返回false，否则返回trueSystem.out.println(Thread.currentThread().getName() + ",r:" + r+ ",f:" + f);} while (!f);return r;}}