Groovy里使用CountDownLatch

Latch的字面意思：弹簧锁

CountDownLatch是java.util.concurrent包里的一个同步工具类。

CountDownLatch的构造函数，接收一个类型为整型的参数，代表CountDownLatch所在的线程，在执行await方法后能够返回，所需要在其他线程内调用其countDown方法的次数。

timer.schedule新启动了一个线程，在新线程里调用countDown，而主线程执行await进入阻塞状态，待新线程调用一次countDown之后，主线程立即从await方法的阻塞状态中返回。

package jerry;

import java.util.concurrent.CountDownLatch
import java.util.concurrent.TimeUnit

CountDownLatch called = new CountDownLatch(1)
println "main thread id: " + Thread.currentThread().getId();

Timer timer = new Timer()
timer.schedule(new TimerTask() {
    void run() {
        println "call countDown in another thread: " + Thread.currentThread().getId();
        called.countDown()
    }
}, 220)

println "before calling called.await in main thread: " + Thread.currentThread().getId();
called.await(10, TimeUnit.SECONDS)
println "after calling called.await in main thread: " + Thread.currentThread().getId();