Parallel.ForEach finally clause

Question

I would like to know if there is maybe a finally that i can use in a Parallel.ForEach?

try
{
}
finally
{
}

Is this possible in a Parallel.ForEach?

I need to do a finally when the loop has completed.

Parallel.ForEach(someList, x =>
{
    //...
}, // Now i need to do a finally);

My problem is that i have a try finally around my Parallel.ForEach, but i dont want the finally to happen. It must only happen when the parallel task has completed.

So this does not work for me:

try
{
   Parallel.ForEach(someList, x =>
   {
      //...
   });
}
finally
{
}

Is there maybe another way of doing this?

score 5 · Accepted Answer · edited May 23 '17 at 11:49

5

Loops and finally don't go together (except maybe in Python). You simply write the code to run after the loop, well, after the loop.

If you want to run it regardless of exceptions in the loop, do it like this:

try
{
   Parallel.ForEach(...)
}
finally
{
   // ...
}

On second thought, maybe the OP ment to use this Parallel.ForEach overload, which allows you to provide a "localFinal" action, that is invoked whenever a thread (used to execute one more iterations of the loop) has completed.

edited May 23 '17 at 11:49

Community

1
1

answered May 03 '12 at 13:58

Christian.K

47,778
10
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As a bit of explanation, the reason this works is that `Parallel.ForEach` blocks the current thread until all operations are complete, unlike, e.g., starting a thread, which returns control immediately. – Tim S. May 03 '12 at 14:03
Sorry, but it is quite unclear what you mean by "I don't want the finally to happen" or by "when the task is completed". (1) if you don't want a finally, don't write one. (2) You use the `Parallel` class to abstract from the `Task` class (assuming you're actually referring to that). – Christian.K May 03 '12 at 14:21
Your second thought is correct. =) So there is an overload for this? Do you perhaps have an example for me? – Willem May 03 '12 at 14:26
@Willem check the MSDN page I linked to. They provide an example at/near the bottom – Christian.K May 03 '12 at 14:30

score 2 · Answer 2 · answered May 03 '12 at 14:00

2

You either put a try .. finally block inside the action being performed in parallel, or outside it:

Parallel.ForEach(someList, x =>
{
    try
    {
    }
    finally
    {
    }
});

or:

try
{
    Parallel.ForEach(someList, x =>
    {
    });
}
finally
{
}

It depends on your use case, which isn't clear from the question.

answered May 03 '12 at 14:00

David M

71,481
13
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186

In that case, the latter case works - see Tim S's comment to Christian K's answer. – David M May 03 '12 at 14:25

Parallel.ForEach finally clause

2 Answers2