java java中带有invokeAll()和Future的ExecutorService
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ExecutorService with invokeAll() and Future in java
提问by fen1ksss
Having the following code at hand:
手头有以下代码：
ExecutorService executor = Executors.newFixedThreadPool(10);
Collection collection = new ArrayList();
for (int n=1; n<100; n++)
collection.add(new MyThread(n));
try {
List<Future<Boolean>> futures = executor.invokeAll(collection);
for(Future<Boolean> future : futures){
future.get();
if (future.isDone()) {
System.out.println("true");
}
else
System.out.println("false");
}
} catch (Exception e) {
e.printStackTrace();
}
If the above is correct?
And if all future.isDone()are true, then all of the threads have been done?
How can I make a flag, to be sure that all of them are done?
以上是否正确？
如果一切future.isDone()都是真的，那么所有的线程都已经完成了？
我怎样才能制作一面旗帜，以确保所有这些都完成了？
采纳答案by gabrjan
To check if all are true, you can do something like this:
要检查是否全部正确，您可以执行以下操作：
boolean works=true;
for(Future<Boolean> future : futures){
future.get();
if (future.isDone()) {
System.out.println("true");
}
else{
System.out.println("false");works=false;
}
}
if(works)System.out.println("yea it works")
回答by user1372408
Meant as a comment on vainolo's reply but I don't have enough reputation points:
作为对 vainolo 回复的评论，但我没有足够的声望点：
isDoneis also redundant because invokeAllreturns a list of futures for which isDoneis true. The javadocs mention this.
isDone也是多余的，因为invokeAll返回isDone为真的期货列表。javadocs提到了这一点。
回答by Juvanis
Using a boolean variable is the simplest way to understand that all threads are done. Another way could be using a primitive, e.g. an integer. You could simply increment/decrement the counter to see if all threads are done.
使用布尔变量是理解所有线程都已完成的最简单方法。另一种方法是使用原语，例如整数。您可以简单地增加/减少计数器以查看是否所有线程都已完成。
And another way could be checking the return value of awaitTermination()invocation on your ExecutorServiceobject.
另一种方法可能是检查对象上awaitTermination()调用的返回值ExecutorService。
int counter = 0;
for(Future<Boolean> future : futures)
{
future.get();
if (future.isDone())
System.out.println("true");
else
{
counter++;
System.out.println("false");
}
}
if(counter != 0)
System.out.println("DONE!");
// Another way of checking all threads are done.
if(executor.awaitTermination(100, TimeUnit.SECONDS))
System.out.println("DONE!");
回答by Peter Lawrey
Normally you add Runnable tasks to a Thread pool. Adding Threads to a thread pool isn't going to do what you think.
通常，您将 Runnable 任务添加到线程池中。将线程添加到线程池不会按照您的想法行事。
When future.get() returns for each task, all the tasks have completed. The threads which ran the tasks will still be running.
当 future.get() 为每个任务返回时，所有任务都已完成。运行任务的线程仍将运行。
If you want to stop all the thread once the tasks have completed you can use executor.shutdown();and executor.awaitTermination
如果您想在任务完成后停止所有线程，您可以使用executor.shutdown();和executor.awaitTermination
The way I would write it is
我会写它的方式是
ExecutorService executor = Executors.newFixedThreadPool(10);
List<Future<Boolean>> futures = new ArrayList<>();
for (int n = 0; n < 100; n++)
futures .add(executor.submit(new MyTask(n));
for(Future<Boolean> future : futures) {
boolean result = future.get();
// do something with the result.
}
If the result is not needed to you make the type Future<Void>or Future<?>or just Future
如果结果不需要您制作类型Future<Void>或Future<?>或只是Future
回答by saum22
initialize a variable check with value =1 and update the value in the else .then check the value of check after the loop has executed
用值 =1 初始化一个变量检查并更新 else 中的值。然后在循环执行后检查 check 的值
if (future.isDone()) {
System.out.println("true");
}
else
{System.out.println("false");
check=0;}
回答by vainolo
If the method future.getreturns then the computation done by the future is finished, so calling isDoneis redundant. And yes, after all futures have finished all of the threads in the ThreadPoolshould be available.
如果方法future.get返回，则未来完成的计算完成，因此调用isDone是多余的。是的，在所有期货都完成之后，ThreadPool应该可以使用中的所有线程。
回答by Vishnu
Invokeall calling this method waits complete all take then CPU execution reaches to for loop to check for completion Or Do we need do .. While loop To check completion of tasks
Invokeall 调用此方法等待完成所有时间，然后 CPU 执行到达 for 循环以检查完成 或者我们需要做 .. While 循环来检查任务的完成
