synchronized修饰static方法与非static方法的区别

╰半橙微兮° 2022-07-21 02:47 196阅读 0赞

### 当synchronized修饰一个static方法时，多线程下，获取的是类锁（即Class本身，注意：不是实例） ###

### 当synchronized修饰一个非static方法时，多线程下，获取的是对象锁（即类的实例对象） ###

看下面2个代码实例1和实例2的对比：

### 实例1 ###

package com.paincupid.springmvc.application.concurrent;
    
    /** * 静态方法 * @author wb-lidongyue * */
    public class SynchronizedStatic1Test { 
    
        public static synchronized void staticX() throws InterruptedException {
            for (int i = 0; i < 10; i++) {
                Thread.sleep(1000);
                System.out.println("staticX.......................");
            }
        }
    
        public synchronized void x() throws InterruptedException {
            for (int i = 0; i < 10; i++) {
                Thread.sleep(1000);
                System.out.println("x.......................");
            }
        }
    
        public static void main(String[] args) {
            final SynchronizedStatic1Test test1 = new SynchronizedStatic1Test();
            Thread thread = new Thread(new Runnable() {
                public void run() {
                    try {
                        test1.x();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }, "a");
    
            Thread thread1 = new Thread(new Runnable() {
                public void run() {
                    try {
                        SynchronizedStatic1Test.staticX();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }, "b");
    
            thread1.start();
            thread.start();
        }
    
    }

结果：

> staticX…………………..  
> x…………………..  
> x…………………..  
> staticX…………………..  
> x…………………..  
> staticX…………………..  
> x…………………..  
> staticX…………………..  
> x…………………..  
> staticX…………………..  
> staticX…………………..  
> x…………………..  
> x…………………..  
> staticX…………………..

### 实例2 ###

package com.paincupid.springmvc.application.concurrent;
    
    public class SynchronizedStatic2Test { 
        public final static Byte[] locks = new Byte[0];
    
        public static void staticX() throws InterruptedException {
            synchronized (locks) {
                for (int i = 0; i < 10; i++) {
                    Thread.sleep(1000);
                    System.out.println("staticX.......................");
                }
            }
        }
    
        public void x() throws InterruptedException {
            synchronized (locks) {
                for (int i = 0; i < 10; i++) {
                    Thread.sleep(1000);
                    System.out.println("x.......................");
                }
            }
        }
    
        public static void main(String[] args) {
            final SynchronizedStatic2Test test1 = new SynchronizedStatic2Test();
            Thread thread = new Thread(new Runnable() {
                public void run() {
                    try {
                        test1.x();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }, "a");
    
            Thread thread1 = new Thread(new Runnable() {
                public void run() {
                    try {
                        SynchronizedStatic2Test.staticX();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }, "b");
    
            thread1.start();
            thread.start();
        }
    }

结果：

> staticX…………………..  
> staticX…………………..  
> staticX…………………..  
> staticX…………………..  
> staticX…………………..  
> staticX…………………..  
> staticX…………………..  
> staticX…………………..  
> staticX…………………..  
> staticX…………………..  
> x…………………..  
> x…………………..  
> x…………………..  
> x…………………..  
> x…………………..  
> x…………………..  
> x…………………..  
> x…………………..  
> x…………………..  
> x…………………..

### 实例3 ###

package com.paincupid.springmvc.application.concurrent;
    
    import java.util.concurrent.atomic.AtomicInteger;
    
    public class SynchronizedStatic3Test extends Thread{ 
            public static int i = 0;  //加不加volatile都一样
            //----------- 解决方案一 ------------------------------------------------------------------
            //public static AtomicInteger i = new AtomicInteger(0); 
    
            //----------- 解决方案二 ------------------------------------------------------------------
            //public static synchronized void inc(){ 此时打印值为1000
            public synchronized void inc(){  //此时值可能永远都不会是1000
                i++;
            }  
            @Override  
            public void run() {  
                for (int x = 0; x < 10; x++) {  
                    inc();  
                    try {  
                        Thread.sleep(33);  
                    } catch (InterruptedException e) {  
                        e.printStackTrace();  
                    }  
                }  
            }  
    
            public static void main(String[] args) throws InterruptedException {  
                SynchronizedStatic3Test sst = new SynchronizedStatic3Test();
                Thread[] t = new Thread[100];
                for (int i = 0; i < t.length; i++) {  
                    t[i] = new Thread(new SynchronizedStatic3Test());  
                }  
                for (int i = 0; i < t.length; i++) {  
                    t[i].start();  
                }  
                for (int i = 0; i < t.length; i++) {  
                    t[i].join();  
                }
                int temp = sst.i;
                System.out.println(temp);
    
               //----------- 解决方案三 ------------------------------------------------------------------
    
                sst = new SynchronizedStatic3Test();
                t = new Thread[100];
                for (int i = 0; i < t.length; i++) {  
                    t[i] = new Thread(sst);
                }  
                for (int i = 0; i < t.length; i++) {  
                    t[i].start();  
                }  
                for (int i = 0; i < t.length; i++) {  
                    t[i].join();  
                }  
                System.out.println(sst.i - temp);
            }  
    
        }

参考：[http://blog.csdn.net/virgoboy2004/article/details/7585182][http_blog.csdn.net_virgoboy2004_article_details_7585182]

[http://blog.csdn.net/hey\_a\_hao/article/details/10155503][http_blog.csdn.net_hey_a_hao_article_details_10155503]

[http_blog.csdn.net_virgoboy2004_article_details_7585182]: http://blog.csdn.net/virgoboy2004/article/details/7585182
[http_blog.csdn.net_hey_a_hao_article_details_10155503]: http://blog.csdn.net/hey_a_hao/article/details/10155503