取消在 ScheduledExecutorService 中安排的任务可使执行程序保持活动状态

Question

这已经困扰我几个小时了。如果我安排一个任务在 5 秒内执行 然后立即取消该任务，我希望 "awaitTermination" 方法立即 return，但它会一直阻塞 7 秒 （不是五秒）..

这是重现 Java11 上的问题的 JUnit 5 测试用例。

package dummy;

import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Test;

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;

import static org.junit.jupiter.api.Assertions.assertFalse;
import static org.junit.jupiter.api.Assertions.fail;

class DummyTest {

  @Test
  @DisplayName("Cancelling task should work...")
  void cancel_task() throws InterruptedException {
    ScheduledExecutorService executorService = Executors.newSingleThreadScheduledExecutor();

    AtomicBoolean isExecuted = new AtomicBoolean(false);
    ScheduledFuture<?> scheduled = executorService.schedule(() -> isExecuted.set(true), 5, TimeUnit.SECONDS);
    scheduled.cancel(false);

    if (!executorService.awaitTermination(7, TimeUnit.SECONDS)) {
      fail("Didn't shut down within timeout"); // <-- Fails here
    }

    assertFalse(isExecuted.get(), "Task should be cancelled before executed");
  }

}

有什么想法吗？

Answer 1

您不在 executorService 上调用 shutdown 或 shutdownNow，因此您可以永远等待。它永远不会终止。先调用关闭，然后单元测试应该工作。

scheduled.cancel(false);
executorService.shutdown(); // This was missing
if (!executorService.awaitTermination(7, TimeUnit.SECONDS)) {
...

awaitTermination "Blocks until all tasks have completed execution after a shutdown request, or the timeout occurs, or the current thread is interrupted, whichever happens first"（从评论中复制，感谢 ptomli）。

取消在 ScheduledExecutorService 中安排的任务可使执行程序保持活动状态

Cancelling a task scheduled in a ScheduledExecutorService keeps executor alive

java

scheduledexecutorservice