CountDownLatch is often used to monitor certain initialization operations, and notify the current thread to continue working after the initialization operation is completed.
In the following code, thread 1 will block at countDown.await() and need to wait for threads 2 and 3
import java.util.concurrent.CountDownLatch;
public class P01CountDownLatch
{
public static void main(String[] args)
{
//2 means to wait for countDown() twice
final CountDownLatch countDown = new CountDownLatch(2);
Thread t1 = new Thread(new Runnable()
{
@Override
public void run()
{
try
{
System.out.println("Enter thread t1, waiting for other threads to finish processing");
countDown.await();//Need to wait
System.out.println("t1 thread continues to execute");
}
catch (InterruptedException e)
{
// TODO Auto-generated catch block
e.printStackTrace ();
}
}
});
Thread t2 = new Thread(new Runnable()
{
@Override
public void run()
{
try
{
System.out.println("Enter thread t2");
Thread.sleep(2000);
countDown.countDown();
System.out.println("The t2 thread is executed, notify the t1 thread to continue executing");
}
catch (InterruptedException e)
{
// TODO Auto-generated catch block
e.printStackTrace ();
}
}
});
Thread t3 = new Thread(new Runnable()
{
@Override
public void run()
{
try
{
System.out.println("Enter thread t3");
Thread.sleep(3000);
countDown.countDown();//If this line is commented out, the t1 thread will never execute again
System.out.println("The t3 thread is executed, notify the t1 thread to continue executing");
}
catch (InterruptedException e)
{
// TODO Auto-generated catch block
e.printStackTrace ();
}
}
});
t1.start();
t2.start();
t3.start();
}
}
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