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[英]How to wait for all tasks in an ThreadPoolExecutor to finish without shutting down the Executor?
[英]How to wait for a ThreadPoolExecutor to finish
我的问题:如何在ThreadPoolExecutor
上执行一堆线程对象并等待它们全部完成后再继续?
我是 ThreadPoolExecutor 的新手。 所以这段代码是一个测试,以了解它是如何工作的。 现在我什至没有用对象填充BlockingQueue
因为我不明白如何在不使用另一个RunnableObject
调用execute()
情况下启动队列。 无论如何,现在我只是调用awaitTermination()
但我想我仍然缺少一些东西。 任何提示都会很棒! 谢谢。
public void testThreadPoolExecutor() throws InterruptedException {
int limit = 20;
BlockingQueue q = new ArrayBlockingQueue(limit);
ThreadPoolExecutor ex = new ThreadPoolExecutor(limit, limit, 20, TimeUnit.SECONDS, q);
for (int i = 0; i < limit; i++) {
ex.execute(new RunnableObject(i + 1));
}
ex.awaitTermination(2, TimeUnit.SECONDS);
System.out.println("finished");
}
RunnableObject 类:
package playground;
public class RunnableObject implements Runnable {
private final int id;
public RunnableObject(int id) {
this.id = id;
}
@Override
public void run() {
System.out.println("ID: " + id + " started");
try {
Thread.sleep(2354);
} catch (InterruptedException ignore) {
}
System.out.println("ID: " + id + " ended");
}
}
你应该循环awaitTermination
ExecutorService threads;
// ...
// Tell threads to finish off.
threads.shutdown();
// Wait for everything to finish.
while (!threads.awaitTermination(10, TimeUnit.SECONDS)) {
log.info("Awaiting completion of threads.");
}
您的问题似乎是在将所有作业提交到池后没有调用shutdown
。 如果没有shutdown()
您的awaitTermination
将始终返回 false。
ThreadPoolExecutor ex =
new ThreadPoolExecutor(limit, limit, 20, TimeUnit.SECONDS, q);
for (int i = 0; i < limit; i++) {
ex.execute(new RunnableObject(i + 1));
}
// you are missing this line!!
ex.shutdown();
ex.awaitTermination(2, TimeUnit.SECONDS);
您还可以执行以下操作以等待所有作业完成:
List<Future<Object>> futures = new ArrayList<Future<Object>>();
for (int i = 0; i < limit; i++) {
futures.add(ex.submit(new RunnableObject(i + 1), (Object)null));
}
for (Future<Object> future : futures) {
// this joins with the submitted job
future.get();
}
...
// still need to shutdown at the end
ex.shutdown();
此外,因为您睡眠了2354
毫秒,但只等待所有作业终止2
SECONDS
, awaitTermination
将始终返回false
。 我会使用Long.MAX_VALUE
来等待作业完成。
最后,听起来您担心创建一个新的ThreadPoolExecutor
而您想要重用第一个。 别这样与您为检测作业是否完成而编写的任何代码相比,GC 开销将非常小。
引用 javadocs 中的ThreadPoolExecutor.shutdown()
:
启动有序关闭,其中执行先前提交的任务,但不会接受新任务。 如果已经关闭,调用没有额外的效果。
在ThreadPoolExecutor.awaitTermination(...)
方法中,它正在等待执行器的状态转到TERMINATED
。 但首先,国家必须去SHUTDOWN
如果shutdown()
被调用或STOP
如果shutdownNow()
被调用。
这与执行者本身无关。 只需使用接口的java.util.concurrent.ExecutorService.invokeAll(Collection<? extends Callable<T>>)
。 它将阻塞,直到所有Callable
完成。
Executors 应该是长寿的; 超出一组任务的生命周期。 shutdown
用于应用程序完成并清理时。
这是已接受的答案的一个变体,它在抛出 InterruptedException 时处理重试:
executor.shutdown();
boolean isWait = true;
while (isWait)
{
try
{
isWait = !executor.awaitTermination(10, TimeUnit.SECONDS);
if (isWait)
{
log.info("Awaiting completion of bulk callback threads.");
}
} catch (InterruptedException e) {
log.debug("Interruped while awaiting completion of callback threads - trying again...");
}
}
另一种方法是使用 CompletionService,如果您必须尝试任何任务结果,这将非常有用:
//run 3 task at time
final int numParallelThreads = 3;
//I used newFixedThreadPool for convenience but if you need you can use ThreadPoolExecutor
ExecutorService executor = Executors.newFixedThreadPool(numParallelThreads);
CompletionService<String> completionService = new ExecutorCompletionService<String>(executor);
int numTaskToStart = 15;
for(int i=0; i<numTaskToStart ; i++){
//task class that implements Callable<String> (or something you need)
MyTask mt = new MyTask();
completionService.submit(mt);
}
executor.shutdown(); //it cannot be queued more task
try {
for (int t = 0; t < numTaskToStart ; t++) {
Future<String> f = completionService.take();
String result = f.get();
// ... something to do ...
}
} catch (InterruptedException e) {
//termination of all started tasks (it returns all not started tasks in queue)
executor.shutdownNow();
} catch (ExecutionException e) {
// ... something to catch ...
}
试试这个,
ThreadPoolExecutor ex =
new ThreadPoolExecutor(limit, limit, 20, TimeUnit.SECONDS, q);
for (int i = 0; i < limit; i++) {
ex.execute(new RunnableObject(i + 1));
}
要添加的行
ex.shutdown();
ex.awaitTermination(timeout, unit)
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