java synchronized/wait/notify/互斥/同步

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1.互斥问题

synchronized关键字，天生互斥，只用这个关键字就能实现互斥。两个线程有一个共同的锁lock，那么其中一个拿到lock，另一个就要等待。模型如下：

thread A:

synchronized(lock){

//do

}

thread B:

synchronized(lock){

//do

}

这两个线程的两个synchronized块中的代码是互斥的。

代码如下：两个类SynchronizeTest / SynchronizeTest1

package spidercsdn;public class SynchronizeTest implements Runnable{public Object lock = new Object();public static SynchronizeTest instance = null;public Object getLock(){return lock;}public static synchronized SynchronizeTest getInstance() {if(instance==null)instance = new SynchronizeTest();return instance;}public void setName() throws InterruptedException{synchronized(lock){System.out.println("lock inner");Thread.sleep(10000);System.out.println("after sleep,you can print");}Thread.sleep(10000);System.out.println("lock outter");}public static void main(String[] args) throws InterruptedException {new Thread(SynchronizeTest.getInstance()).start();new Thread(new SynchronizeTest1()).start();}@Overridepublic void run() {try {SynchronizeTest.getInstance().setName();} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}

package spidercsdn;public class SynchronizeTest1 implements Runnable{public void setName(){synchronized (SynchronizeTest.getInstance().getLock()) {System.out.println("inner st1");}System.out.println("outter st1");}public static void main(String[] args) {}@Overridepublic void run() {SynchronizeTest1 st1 = new SynchronizeTest1();st1.setName();}}

2.wait notify实现的同步问题

wait notify都要出现在synchronized语句块中，一旦wait,wait后面的语句无论在synchronized里面还是外面，一律全都不执行了，让出cpu。

一旦notify，notify后面的语句照常执行，并且通知wait的线程继续执行，但是，只有notify语句后面的在synchronized块中当语句执行完，wait的线程才继续，而notify语句后面的在synchronized块外的代码无所谓，没有特殊性，谁也不用等他执行完。

代码如下：两个类SynchronizeTest / SynchronizeTest1

package spidercsdn;public class SynchronizeTest implements Runnable{public Object lock = new Object();public static SynchronizeTest instance = null;public Object getLock(){return lock;}public static synchronized SynchronizeTest getInstance() {if(instance==null)instance = new SynchronizeTest();return instance;}public void setName() throws InterruptedException{synchronized(lock){System.out.println("11111111");Thread.sleep(10000);System.out.println("22222222");lock.wait();System.out.println("55555555");}System.out.println("66666666");}public static void main(String[] args) throws InterruptedException {new Thread(SynchronizeTest.getInstance()).start();new Thread(new SynchronizeTest1()).start();}@Overridepublic void run() {try {SynchronizeTest.getInstance().setName();} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}

package spidercsdn;public class SynchronizeTest1 implements Runnable{public void setName() throws InterruptedException{synchronized (SynchronizeTest.getInstance().getLock()) {System.out.println("33333333");SynchronizeTest.getInstance().getLock().notify();Thread.sleep(10000);System.out.println("44444444");}Thread.sleep(10000);System.out.println("7777777");}@Overridepublic void run() {SynchronizeTest1 st1 = new SynchronizeTest1();try {st1.setName();} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}

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