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⛺️稳重求进，晒太阳

必须先2后1打印

用synchronized

package aaa;public class Test2 {static Boolean hasExecutor=false;public static void main(String[] args) {Object obj=new Object();new Thread(()->{synchronized (obj){while (!hasExecutor){try {obj.wait();} catch (InterruptedException e) {throw new RuntimeException(e);}}System.out.println(1);}}).start();new Thread(()->{synchronized (obj){System.out.println(2);hasExecutor=true;obj.notifyAll();}}).start();}
}

用ReentrantLock

static Boolean hasExecutor=false;public static void main(String[] args) {ReentrantLock lock=new ReentrantLock();Condition condition = lock.newCondition();new Thread(()->{lock.lock();try {while (!hasExecutor){condition.await();}System.out.println(1);} catch (InterruptedException e) {throw new RuntimeException(e);} finally {lock.unlock();}}).start();new Thread(()->{lock.lock();try {System.out.println(2);hasExecutor=true;condition.signalAll();}finally {lock.unlock();}}).start();}

park && unpark

 

static Boolean hasExecutor=false;public static void main(String[] args) {Object obj=new Object();Thread t1= new Thread(()->{while (!hasExecutor){LockSupport.park();}System.out.println(1);});t1.start();new Thread(()->{synchronized (obj){System.out.println(2);hasExecutor=true;LockSupport.unpark(t1);}}).start();}

交替输出abc

用synchronized

package aaa;public class Test2 {static Boolean hasExecutor = false;public static void main(String[] args) {WaitNotify waitNotify=new WaitNotify(1);new Thread(()->{waitNotify.print("a",1,2);}).start();new Thread(()->{waitNotify.print("b",2,3);}).start();new Thread(()->{waitNotify.print("c",3,1);}).start();}
}class WaitNotify {private Integer flag;public String str="a";public Integer waitFlag;public Integer nextFlag;public WaitNotify(Integer flag) {this.flag=flag;}void print(String str, Integer waitFlag, Integer nextFlag) {while (true) {synchronized (this) {while (waitFlag != flag) {try {this.wait();} catch (InterruptedException e) {throw new RuntimeException(e);}}System.out.print(str);flag=nextFlag;this.notifyAll();}}}}

用reentrantLock()实现

• lock.lock()对应synchronized
• condition.await对应wait()
• condition.signalAll 对应 notifyAll

void printLock(String str, Integer waitFlag, Integer nextFlag) {while (true) {reentrantLock.lock();try {while (waitFlag != flag) {try {condition.await();} catch (InterruptedException e) {throw new RuntimeException(e);}}System.out.print(str);flag=nextFlag;condition.signalAll();}finally {reentrantLock.unlock();}}
}

用park&unpark

park不需要while（）来判断是否虚假唤醒，因为它指定某个线程唤醒

void printPark(String str,Thread t){while (true) {LockSupport.park();System.out.print(str);flag = nextFlag;LockSupport.unpark(t);}}

结合 线程状态思考