await & signal & signalAll
Condition
java.util.concurrent类库中提供Condition类来实现线程之间的协调。
调用Condition.await() 方法使线程等待，其他线程调用Condition.signal() 或 Condition.signalAll() 方法唤醒等待的线程。
- 上锁类
public class TestObject {
private Lock lock = new ReentrantLock();
private Condition condition = lock.newCondition();
public void first() {
System.out.println("first is lock");
lock.lock();
try {
System.out.println("first is running");
condition.signalAll();
} finally {
System.out.println("first is unlock");
lock.unlock();
}
}
public void second() {
System.out.println("second is lock");
lock.lock();
try {
condition.await();
System.out.println("second is running");
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
System.out.println("second is unlock");
lock.unlock();
}
}
public void third() {
System.out.println("third is lock");
lock.lock();
try {
condition.await();
System.out.println("third is running");
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
System.out.println("third is unlock");
lock.unlock();
}
}
}
- 测试类
public class TestRun {
private final static ExecutorService executorService = Executors.newCachedThreadPool();
public static void main(String[] arg) {
TestObject to = new TestObject();
executorService.execute(() -> to.third());
executorService.execute(() -> to.second());
executorService.execute(() -> to.first());
}
}
- 输出结果
third is lock second is lock first is lock first is running first is unlock third is running third is unlock second is running second is unlock
备注：上述实例中，若first方法中改为condition.signal()则second不会被唤醒，需要在third方法的finally中增加condition.signal()才能唤醒second。
wait() & await()
- wait()是Object类中的方法，await()是Condition类里面的方法
- await的阻塞需要Lock中的Condition对象来触发
- await会导致当前线程被阻塞，会释放锁，这点和wait是一样的
- await使用signal唤醒；wait使用notify
- await只能用于ReentrantLock锁中，wait一般用于Synchronized中
正文到此结束
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