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Java基础之线程原子量

2024-08-11 18:53:52   223人阅读

    所谓的原子量即操作变量的操作是“原子的”，该操作不可再分，因此是线程安全的。为何要使用原子变量呢，原因是多个线程对单个变量操作也会引起一些问题。在Java5之前，可以通过volatile、synchronized关键字来解决并发访问的安全问题，但这样太麻烦。Java5之后，专门提供了用来进行单变量多线程并发安全访问的工具包java.util.concurrent.atomic，其中的类也很简单

package unit_fifteen;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.atomic.AtomicLong;/** * Java线程：新特征-原子量* */ public class Test {        public static void main(String[] args) {                ExecutorService pool = Executors.newFixedThreadPool(2);                 Runnable t1 = new MyRunnable("张三", 2000);                Runnable t2 = new MyRunnable("李四", 3600);                Runnable t3 = new MyRunnable("王五", 2700);                Runnable t4 = new MyRunnable("老张", 600);                Runnable t5 = new MyRunnable("老牛", 1300);                Runnable t6 = new MyRunnable("胖子", 800);                //执行各个线程                pool.execute(t1);                 pool.execute(t2);                 pool.execute(t3);                 pool.execute(t4);                 pool.execute(t5);                 pool.execute(t6);                 //关闭线程池                pool.shutdown();         } } class MyRunnable implements Runnable {        private static AtomicLong aLong =new AtomicLong(10000);        //原子量，每个线程都可以自由操作        private String name;                //操作人        private int x;                            //操作数额        MyRunnable(String name, int x) {                this.name = name;                this.x = x;        }         public void run() {                System.out.println(name + "执行了" + x +"，当前余额：" + aLong.addAndGet(x));        } }

上面是个反例，代码的结果是多变的

注意：原子量虽然可以保证单个变量在某一个操作过程的安全，但无法保证你整个代码块，或者整个程序的安全性。因此，通常还应该使用锁等同步机制来控制整个程序的安全性

package unit_fifteen;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantLock;import java.util.concurrent.atomic.AtomicLong;/** * Java线程：新特征-原子量* */ public class Test {        public static void main(String[] args) {                ExecutorService pool = Executors.newFixedThreadPool(2);                 Lock lock = new ReentrantLock(false);                Runnable t1 = new MyRunnable("张三", 2000,lock);                Runnable t2 = new MyRunnable("李四", 3600,lock);                Runnable t3 = new MyRunnable("王五", 2700,lock);                Runnable t4 = new MyRunnable("老张", 600,lock);                Runnable t5 = new MyRunnable("老牛", 1300,lock);                Runnable t6 = new MyRunnable("胖子", 800,lock);                //执行各个线程                pool.execute(t1);                 pool.execute(t2);                 pool.execute(t3);                 pool.execute(t4);                 pool.execute(t5);                 pool.execute(t6);                 //关闭线程池                pool.shutdown();         } } class MyRunnable implements Runnable {        private static AtomicLong aLong =new AtomicLong(10000);        //原子量，每个线程都可以自由操作        private String name;                //操作人        private int x;                            //操作数额        private Lock lock;        MyRunnable(String name, int x,Lock lock) {                this.name = name;                this.x = x;                this.lock = lock;        }         public void run() {                lock.lock();                 System.out.println(name + "执行了" + x +"，当前余额：" + aLong.addAndGet(x));                lock.unlock();         } }

 

Java基础之线程原子量


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