Java 如何检查 ExecutorService 上运行的所有任务是否已完成
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How to check if all tasks running on ExecutorService are completed
提问by user4129715
I'v got ConcurrentLinkedDeque which I'm using for synchronic push/pop elements, and I'v got some async tasks which are taking one element from stack and if this element has neighbors It's pushing it to stack.
我有 ConcurrentLinkedDeque 用于同步推送/弹出元素，我有一些异步任务从堆栈中获取一个元素，如果这个元素有邻居，它会将它推送到堆栈。
Example code:
示例代码：
private ConcurrentLinkedDeque<Item> stack = new ConcurrentLinkedDeque<>();
private ExecutorService exec = Executors.newFixedThreadPool(5);
while ((item = stack.pollFirst()) != null) {
if (item == null) {
} else {
Runnable worker = new Solider(this, item);
exec.execute(worker);
}
}
class Solider{
public void run(){
if(item.hasNeighbors){
for(Item item:item.neighbors){
stack.push(item)
}
}
}
}
I would like to have additional statement in while loop which answers the question - "any task in Executor is working?"
我想在 while 循环中有额外的语句来回答这个问题——“Executor 中的任何任务都在工作？”
采纳答案by Andy Guibert
There isn't a clean way to check if all Runnables are done if you use ExecutorService.execute(Runnable). Unless you build a mechanism to do so in the Runnable itself (which is sloppy in my opinion).
如果您使用ExecutorService.execute(Runnable). 除非您在 Runnable 本身中构建了一个机制来这样做（在我看来这很草率）。
Instead:
Use ExecutorService.submit(Runnable). This method will return a Future<?>which is a handle to the result of a Runnable. Using Futures provides a clean way to check results.
相反：
使用ExecutorService.submit(Runnable). 此方法将返回 a Future<?>，它是 a 的结果的句柄Runnable。使用 Futures 提供了一种干净的方法来检查结果。
All you have to do is maintain a list of Futures that you submit, and then you can iterate over the whole list of Futures and either:
A) wait for all the futures to be done in a blocking way or
B) check if all the futures are done in a non-blocking way.
您所要做的就是维护您提交的期货列表，然后您可以遍历整个期货列表，并且：
A）等待所有期货以阻塞方式完成或
B）检查是否所有期货期货以非阻塞方式完成。
Here is a code example:
这是一个代码示例：
List<Future<?>> futures = new ArrayList<Future<?>>();
ExecutorService exec = Executors.newFixedThreadPool(5);
// Instead of using exec.execute() use exec.submit()
// because it returns a monitorable future
while((item = stack.pollFirst()) != null){
Runnable worker = new Solider(this, item);
Future<?> f = exec.submit(worker);
futures.add(f);
}
// A) Await all runnables to be done (blocking)
for(Future<?> future : futures)
future.get(); // get will block until the future is done
// B) Check if all runnables are done (non-blocking)
boolean allDone = true;
for(Future<?> future : futures){
allDone &= future.isDone(); // check if future is done
}
回答by Carlos Sanchez
Update: with Java 8+ CompletableFutures you can manage this with its new callback functions. First you will need to create all of the CompletableFutures you need which will also start running, eg:
更新：使用 Java 8+ CompletableFutures，您可以使用其新的回调函数来管理它。首先，您需要创建您需要的所有 CompletableFutures，它们也将开始运行，例如：
We need to accumulate all the futures generated in an Array in order to pass them later to CompletableFuture.allOf(CompletableFutures...)
我们需要累积在 Array 中生成的所有期货，以便稍后将它们传递给 CompletableFuture.allOf(CompletableFutures...)
So let's say you have a list of people you want to calculate its days until birthday asynchronously:
因此，假设您有一个要异步计算其生日前天数的人员列表：
First we create all those needed futures and collect them together in an array:
首先，我们创建所有需要的期货并将它们收集在一个数组中：
CompletableFuture<?>[] completables = people.stream()
.map(p -> createCompletableFuture(p))
.toArray(CompletableFuture<?>[]::new);
private CompletableFuture createCompletableFuture(Person p) {
return CompletableFuture.runAsync(daysUntillBirthday(p));
}
Then you pass those completables to a new CompletableFuture:
然后将这些可完成项传递给新的 CompletableFuture：
CompletableFuture c = CompletableFuture.allOf(completables)
And you can now check if there are still futures running with:
您现在可以检查是否仍有期货在运行：
c.isDone()
