Lock中使用Condition实现等待通知
2024-09-03 22:24:41
- Condition类有很好的灵活性，可以实现多路通知功能，一个Lock对象中可以创建多个Condition对象实例，线程对象可以注册在指定的Condition中，进而有选择的进行线程通知，在调度线程上更加灵活
- wait与notify/notifyAll进行等待通知时，被通知的线程是随机的，但是Condition与Lock结合的通知是有选择性的通知
- synchronized就相当于整个Lock对象中只有一个单一的Condition对象，所有线程对象都注册在一个Condition对象身上，线程开始notifyAll时，需要通知所有的WAITING线程，没有选择性，会出现很大的效率问题
public class MyService {
private Lock lock = new ReentrantLock();
public Condition condition = lock.newCondition();
public void await(){
try {
lock.lock();
System.out.println("await时间为"+System.currentTimeMillis());
condition.await();
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void signal(){
try {
lock.lock();
System.out.println("signal时间为"+System.currentTimeMillis());
condition.signal();
} finally {
lock.unlock();
}
}
}
public class MyThread extends Thread {
private MyService service;
public MyThread(MyService service) {
this.service = service;
}
@Override
public void run() {
service.await();
}
}
public class Run {
public static void main(String[] args) {
try {
MyService service = new MyService();
MyThread mt = new MyThread(service);
mt.start();
Thread.sleep(3000);
service.signal();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
-------------------------------------------------------打印输出-------------------------------------------------------
await时间为1537949157830
signal时间为1537949160830
Condition类中的await方法相当于Object类中的wait方法
Condition类中的signal/signalAll方法相当于Object类中的notify/notifyAll方法
案例2
public class MyService {
private Lock lock = new ReentrantLock();
public Condition condition = lock.newCondition();
public void awaitA(){
try {
lock.lock();
System.out.println("begin awaitA时间为"+System.currentTimeMillis()+ " ThreadName="+Thread.currentThread().getName());
condition.await();
System.out.println("end awaitA时间为"+System.currentTimeMillis()+ " ThreadName="+Thread.currentThread().getName());
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void awaitB(){
try {
lock.lock();
System.out.println("begin awaitB时间为"+System.currentTimeMillis()+ " ThreadName="+Thread.currentThread().getName());
condition.await();
System.out.println("end awaitB时间为"+System.currentTimeMillis()+ " ThreadName="+Thread.currentThread().getName());
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void signalAll(){
try {
lock.lock();
System.out.println("signalAll时间为"+System.currentTimeMillis()+ " ThreadName="+Thread.currentThread().getName());
condition.signalAll();
} finally {
lock.unlock();
}
}
}
线程
public class ThreadA extends Thread {
private MyService service;
public ThreadA(MyService service) {
this.service = service;
}
@Override
public void run() {
service.awaitA();
}
}
-------------------------------------------------
public class ThreadB extends Thread {
private MyService service;
public ThreadB(MyService service) {
this.service = service;
}
@Override
public void run() {
service.awaitB();
}
}
public class Run {
public static void main(String[] args) throws InterruptedException {
MyService service = new MyService();
ThreadA a = new ThreadA(service);
a.setName("A");
ThreadB b = new ThreadB(service);
b.setName("B");
a.start();
b.start();
Thread.sleep(3000);
service.signalAll();
}
}
-------------------------------------------------------打印输出-------------------------------------------------------
begin awaitA时间为1537951494924 ThreadName=A
begin awaitB时间为1537951494925 ThreadName=B
signalAll时间为1537951497924 ThreadName=main
end awaitA时间为1537951497924 ThreadName=A
end awaitB时间为1537951497925 ThreadName=B
线程A和B都被唤醒了
使用多个Condition实现通知部分线程
想要单独唤醒部分线程，就需要使用多个Condition对象，先对线程进行分组，Condition对象可以唤醒部分指定线程，有助于提高程序运行效率
public class MyService {
private Lock lock = new ReentrantLock();
public Condition conditionA = lock.newCondition();
public Condition conditionB = lock.newCondition();
public void awaitA(){
try {
lock.lock();
System.out.println("begin awaitA时间为"+System.currentTimeMillis()+" ThreadName="+Thread.currentThread().getName());
conditionA.await();
System.out.println("--end awaitA时间为"+System.currentTimeMillis()+" ThreadName="+Thread.currentThread().getName());
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void awaitB(){
try {
lock.lock();
System.out.println("begin awaitB时间为"+System.currentTimeMillis()+" ThreadName="+Thread.currentThread().getName());
conditionB.await();
System.out.println("--end awaitB时间为"+System.currentTimeMillis()+" ThreadName="+Thread.currentThread().getName());
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void signAll_A(){
try {
lock.lock();
System.out.println("signAll_A时间为"+System.currentTimeMillis()+" ThreadName="+Thread.currentThread().getName());
conditionA.signalAll();
} finally {
lock.unlock();
}
}
public void signAll_B(){
try {
lock.lock();
System.out.println("signAll_B时间为"+System.currentTimeMillis()+" ThreadName="+Thread.currentThread().getName());
conditionB.signalAll();
} finally {
lock.unlock();
}
}
}
线程
public class ThreadA extends Thread {
private MyService service;
public ThreadA(MyService service) {
this.service = service;
}
@Override
public void run() {
service.awaitA();
}
}
-----------------------------------------------
public class ThreadB extends Thread {
private MyService service;
public ThreadB(MyService service) {
this.service = service;
}
@Override
public void run() {
service.awaitB();
}
}
public class Run {
public static void main(String[] args) throws InterruptedException {
MyService service = new MyService();
ThreadA a = new ThreadA(service);
a.setName("A");
ThreadB b = new ThreadB(service);
b.setName("B");
a.start();
b.start();
Thread.sleep(3000);
service.signAll_A();
}
}
-------------------------------------------------------打印输出-------------------------------------------------------
begin awaitA时间为1537952328573 ThreadName=A
begin awaitB时间为1537952328573 ThreadName=B
signAll_A时间为1537952331572 ThreadName=main
--end awaitA时间为1537952331572 ThreadName=A
线程A被唤醒了，但是线程B仍然在等待
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