synchronized 到底锁的是谁?"/>
synchronized 到底锁的是谁?
synchronized 到底锁的是谁?
修饰方法:
1、静态方法
2、非静态方法,锁住的是方法的调用者
修饰代码块
1、synchronized修饰非静态方法 锁住的是方法的调用者
锁住实例
流程:
1、线程A先拿到synModel对象然后给这个 synModel对象加上锁–接着等3s执行输出结束
2、线程B等1s后运行,此时 synModel对象 已经被 A拿到,所以他只能等待 等3s后,线程A释放 synModel对象,然后获取对象执行输出结束
public class SynchronizedTest {public static void main(String[] args) throws InterruptedException {SynModel synModel = new SynModel();new Thread(()->{synModel.fun1();},"A").start();TimeUnit.SECONDS.sleep(1);new Thread(()->{synModel.fun2();},"B").start();}
}
class SynModel{public synchronized void fun1() {try {TimeUnit.SECONDS.sleep(3);} catch (InterruptedException e) {e.printStackTrace();}System.out.println("1...");}public synchronized void fun2(){System.out.println("2...");}
}
情况1 不会排队
注意:下面这种情况是不会排队的,因为锁的是实例。
public class SynchronizedTest {public static void main(String[] args) throws InterruptedException {SynModel synModel1 = new SynModel();SynModel synModel2 = new SynModel();new Thread(()->{synModel1.fun1();},"A").start();TimeUnit.SECONDS.sleep(1);new Thread(()->{synModel2.fun2();},"B").start();}
}
class SynModel{public synchronized void fun1() {try {TimeUnit.SECONDS.sleep(3);} catch (InterruptedException e) {e.printStackTrace();}System.out.println("1...");}public synchronized void fun2(){System.out.println("2...");}
}
2 、修饰静态方法
只是把SynModel中的方法变成了静态的,注意此时锁住的是 SynModel这个类,不是锁的实例。会排队 先输出1后输出2
public class SynchronizedTest {public static void main(String[] args) throws InterruptedException {SynModel synModel1 = new SynModel();SynModel synModel2 = new SynModel();new Thread(()->{synModel1.fun1();},"A").start();TimeUnit.SECONDS.sleep(1);new Thread(()->{synModel2.fun2();},"B").start();}
}
class SynModel{public static synchronized void fun1() {try {TimeUnit.SECONDS.sleep(3);} catch (InterruptedException e) {e.printStackTrace();}System.out.println("1...");}public static synchronized void fun2(){System.out.println("2...");}
}
3、代码块
synchronized (this){}
锁住的是SynModel这个对象。可以看到循环的五次都是同一个SynModel对象。所以五个线程 某个时刻只能有一个线程拿到这个SynModel对象 这个资源。
每个线程会依次输出start end
public class SynchronizedTest {public static void main(String[] args) {final SynModel synModel = new SynModel();for (int i = 0; i < 5; i++) {synModel.fun3();}}
}
class SynModel{public void fun3(){synchronized (this){System.out.println("start");try {TimeUnit.SECONDS.sleep(1);} catch (InterruptedException e) {e.printStackTrace();}System.out.println("end");}}}
如果把对象放在循环里面,此时就是五个线程拿五个资源了。并没有去争夺资源
public class SynchronizedTest {public static void main(String[] args) {for (int i = 0; i < 5; i++) {final SynModel synModel = new SynModel();new Thread(()->{synModel.fun3();}).start();}}
}
class SynModel{public void fun3(){synchronized (this){System.out.println("ThreadName:"+Thread.currentThread().getName()+"start");try {TimeUnit.SECONDS.sleep(1);} catch (InterruptedException e) {e.printStackTrace();}System.out.println("ThreadName:"+Thread.currentThread().getName()+"end");}}}
锁住SynModel.class 此时五个线程就会竞争,因为锁住的是 SynModel这个类,而不是实例对象了。
public class SynchronizedTest {public static void main(String[] args) {for (int i = 0; i < 5; i++) {final SynModel synModel = new SynModel();new Thread(()->{synModel.fun3();}).start();}}
}
class SynModel{public void fun3(){synchronized (SynModel.class){// this SynModel.classSystem.out.println("ThreadName:"+Thread.currentThread().getName()+"start");try {TimeUnit.SECONDS.sleep(1);} catch (InterruptedException e) {e.printStackTrace();}System.out.println("ThreadName:"+Thread.currentThread().getName()+"end");}}}
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