英文:
ScheduledExecutorService not creating concurrent threads
问题
我正在尝试理解ScheduledExecutorService的工作原理。我编写了这个简单的测试：
ScheduledExecutorService executorService = Executors.newScheduledThreadPool(10);
executorService.scheduleAtFixedRate(() -> {
try {
System.out.println("Test " + Thread.currentThread().getId());
Thread.sleep(10000);
System.out.println("End " + Thread.currentThread().getId());
} catch (Exception ex) {
}
}, 0, 100, TimeUnit.MILLISECONDS);
我在控制台上看到以下输出：
Test 19
End 19
Test 19
End 19
Test 21
End 21
依此类推。按理说，执行器应该在第一个线程结束之前就预定并启动一个新线程，如果核心池大小是10，为什么线程会一个接一个地启动？难道不应该有10个线程一起运行吗？
英文:
I am trying to understand how ScheduledExecutorService works. I wrote this simple test:
ScheduledExecutorService executorService = Executors.newScheduledThreadPool(10);
executorService.scheduleAtFixedRate(() -> {
try {
System.out.println("Test " + Thread.currentThread().getId());
Thread.sleep(10000);
System.out.println("End " + Thread.currentThread().getId());
} catch (Exception ex) {
}
}, 0, 100, TimeUnit.MILLISECONDS);
I see following printed on console:
Test 19
End 19
Test 19
End 19
Test 21
End 21
And so on. Shouldn't the executor schedule and start a new thread even before first thread ends? Why are threads started one after the other if core pool size is 10. shouldn't 10 threads run together.
答案1
得分: 6
一个循环任务是不重叠的，因此第一次调用需要在下一次启动之前完成：
> 通过scheduleAtFixedRate或scheduleWithFixedDelay安排的任务的连续执行不会重叠。虽然不同的执行可能由不同的线程执行，但是先前执行的效果会在后续执行之前发生。
> 如果任务的任何执行时间超过其周期，则随后的执行可能会延迟开始，但不会并发执行。
链接：https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ScheduledThreadPoolExecutor.html#scheduleAtFixedRate-java.lang.Runnable-long-long-java.util.concurrent.TimeUnit-
英文:
A recurring task is non-overlapping, so the first invocation would need to finish before the next can start:
> Successive executions of a task scheduled via scheduleAtFixedRate or scheduleWithFixedDelay do not overlap. While different executions may be performed by different threads, the effects of prior executions happen-before those of subsequent ones.
> If any execution of this task takes longer than its period, then subsequent executions may start late, but will not concurrently execute.
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