[英]Why doesn't ScheduledExecutorService spawn threads as needed?
In my application I use ScheduledExecutorService, but only one thread is spawned to handle the scheduled tasks. 在我的应用程序中,我使用ScheduledExecutorService,但仅产生一个线程来处理计划的任务。 Is this because ScheduledExecutorService does not spawn threads to handle the pending tasks?
这是因为ScheduledExecutorService不会生成线程来处理待处理的任务吗?
Here is a code snippet that will output only "run() 1" instead of the expected "run() 1" followed by "run() 2" ... "run() 10." 这是一个代码片段,将仅输出“ run()1”,而不是预期的“ run()1”,后跟“ run()2” ...“ run()10”。
public class App {
public static void main(String[] args) {
int N = 10;
Runnable runner = new Runnable() {
public void run() {
foo();
}
};
for (int i = 0; i < N; i++) {
executor.schedule(runner, i, TimeUnit.MILLISECONDS);
}
}
private static void foo() {
System.out.println("run() " + (++n));
synchronized (executor) {
try {
executor.wait();
} catch (InterruptedException ex) {
Logger.getLogger(App.class.getName()).log(Level.SEVERE, null, ex);
}
}
System.out.println("finished()");
}
private static Logger logger = Logger.getLogger(App.class.getName());
private static int n = 0;
private static ScheduledExecutorService executor = Executors.newScheduledThreadPool(1);
}
There is only one thread because you create the thread pool with Executors.newScheduledThreadPool(1)
, which means that the thread pool contains only 1 thread. 只有一个线程,因为您使用
Executors.newScheduledThreadPool(1)
创建了线程池,这意味着线程池仅包含1个线程。 If you want 10 threads, pass 10 as argument. 如果需要10个线程,则将10作为参数传递。 Note that the documentation of ScheduledThreadPoolExecutor , which is what this method returns, explicitly says that the thread pool has a fixed size.
请注意,此方法返回的ScheduledThreadPoolExecutor文档明确指出线程池的大小是固定的。
From the javadoc for ScheduledThreadPoolExecutor
: 从
ScheduledThreadPoolExecutor
的javadoc中:
While this class inherits from ThreadPoolExecutor, a few of the inherited tuning methods are not useful for it.
尽管此类从ThreadPoolExecutor继承,但是一些继承的调整方法对此没有用。 In particular, because it acts as a fixed-sized pool using corePoolSize threads and an unbounded queue, adjustments to maximumPoolSize have no useful effect.
特别是,由于它使用corePoolSize线程和无限制队列充当固定大小的池,因此对maximumPoolSize的调整没有任何作用。 Additionally, it is almost never a good idea to set corePoolSize to zero or use allowCoreThreadTimeOut because this may leave the pool without threads to handle tasks once they become eligible to run.
另外,将corePoolSize设置为零或使用allowCoreThreadTimeOut几乎不是一个好主意,因为一旦有资格运行任务,这可能会使池中没有线程来处理任务。
In other words, maximumPoolSize == corePoolSize
. 换句话说,
maximumPoolSize == corePoolSize
。 You set corePoolSize
to 1
, so that's all it will spawn. 您将
corePoolSize
设置为1
,这样就可以生成了。
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