我使用CountDownLatch等待来自另一个组件的某个事件(在不同的线程中运行)。以下方法适合我的软件的语义,但我不确定它是否像我期望的那样工作:
mCountDownLatch.await(3000, TimeUnit.MILLISECONDS)
otherComponent.aStaticVolatileVariable = true;
mCountDownLatch.await(3500, TimeUnit.MILLISECONDS);
... <proceed with other stuff>
场景应该如下:我等待3秒钟,如果锁存器没有倒计数到0,我用该变量通知另一个组件,然后我等待最多3.5秒。如果再次出现超时,那么我不在乎并将继续进行其他操作。
注意:我知道它看起来不像那样,但上述场景在我的软件中完全合理且有效。
我确实阅读了await(int,TimeUnit)和CountDownLatch的文档,但我不是Java / Android专家,所以我需要确认。对我来说,所有场景看起来都是有效的:
我是否正确使用等待(...)?即使先前await(...)在同一个对象上超时,也可以以上述方式使用第二个等待(...)吗?
答案 0 :(得分:4)
如果我正确理解您的问题,此测试证明您的所有假设/要求都是真实/满足的。 (使用JUnit和Hamcrest运行。)请注意runCodeUnderTest()
方法中的代码,尽管它中间插入了时间记录,超时时间减少了10倍。
import org.junit.Before;
import org.junit.Test;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import static org.hamcrest.Matchers.closeTo;
import static org.hamcrest.Matchers.lessThan;
import static org.junit.Assert.assertThat;
public class CountdownLatchTest {
static volatile boolean signal;
CountDownLatch latch = new CountDownLatch(1);
long elapsedTime;
long[] wakeupTimes = new long[2];
@Before
public void setUp() throws Exception {
signal = false;
}
@Test
public void successfulCountDownDuringFirstAwait() throws Exception {
countDownAfter(150);
runCodeUnderTest();
assertThat((double) elapsedTime, closeTo(150, 10));
assertThat(wakeupTimeSeparation(), lessThan(10));
}
@Test
public void successfulCountDownDuringSecondAwait() throws Exception {
countDownAfter(450);
runCodeUnderTest();
assertThat((double) elapsedTime, closeTo(450, 10));
assertThat((double) wakeupTimeSeparation(), closeTo(150, 10));
}
@Test
public void neverCountDown() throws Exception {
runCodeUnderTest();
assertThat((double) elapsedTime, closeTo(650, 10));
assertThat((double) wakeupTimeSeparation(), closeTo(350, 10));
}
@Test
public void countDownAfterSecondTimeout() throws Exception {
countDownAfter(1000);
runCodeUnderTest();
assertThat((double) elapsedTime, closeTo(650, 10));
assertThat((double) wakeupTimeSeparation(), closeTo(350, 10));
}
@Test
public void successfulCountDownFromSignalField() throws Exception {
countDownAfterSignal();
runCodeUnderTest();
assertThat((double) elapsedTime, closeTo(300, 10));
}
private int wakeupTimeSeparation() {
return (int) (wakeupTimes[1] - wakeupTimes[0]);
}
private void runCodeUnderTest() throws InterruptedException {
long start = System.currentTimeMillis();
latch.await(300, TimeUnit.MILLISECONDS);
wakeupTimes[0] = System.currentTimeMillis();
signal = true;
latch.await(350, TimeUnit.MILLISECONDS);
wakeupTimes[1] = System.currentTimeMillis();
elapsedTime = wakeupTimes[1] - start;
}
private void countDownAfter(final long millis) throws InterruptedException {
new Thread(new Runnable() {
@Override
public void run() {
sleep(millis);
latch.countDown();
}
}).start();
}
private void countDownAfterSignal() {
new Thread(new Runnable() {
@Override
public void run() {
boolean trying = true;
while (trying) {
if (signal) {
latch.countDown();
trying = false;
}
sleep(5);
}
}
}).start();
}
private void sleep(long millis) {
try {
Thread.sleep(millis);
} catch (InterruptedException e) {
throw new IllegalStateException("Unexpected interrupt", e);
}
}
}