task parallel library not working with inner foreach loops

Question

basically i'm trying run four functions together using task. these four functions runs their own foreach loop. when i'm executing these functions keep getting error. "Collection was modified; enumeration operation may not execute. "

so far methods I have tried:

method 1: fail

var tasks = new[] 
{ 
    Task.Factory.StartNew(() => function1(publishrequest,nextshiftRq, publishList)),
    Task.Factory.StartNew(() => function2(publishrequest,nextshiftRq, publishList)),
    Task.Factory.StartNew(() => function3(publishrequest,nextshiftRq, publishList)),
    Task.Factory.StartNew(() => function4(publishrequest,nextshiftRq, publishList))
};
Task.WaitAll(tasks);

method 2: fail

List<Task> tasks = new List<Task>();
tasks.Add(Task.Factory.StartNew(() => function1(publishrequest, nextshiftRq, publishList)));
tasks.Add(Task.Factory.StartNew(() => function2(publishrequest, nextshiftRq, publishList)));
tasks.Add(Task.Factory.StartNew(() => function3(publishrequest, nextshiftRq, publishList)));
tasks.Add(Task.Factory.StartNew(() => function4(publishrequest, nextshiftRq, publishList)));
Task.WaitAll(tasks.ToArray());

method 3: fail

Parallel.Invoke(
    () = {function1(publishrequest, nextshiftRq, publishList)},
    () = {function2(publishrequest, nextshiftRq, publishList)},
    () = {function3(publishrequest, nextshiftRq, publishList)},
    () = {function4(publishrequest, nextshiftRq, publishList)});

inside in functions

public void function1(publish p1,nextshift nx, List<publish> pub)
{
    foreach(publish in pub.ToList())
    {
       Evaluate.EvaluateShift(p1.publishShift.ShiftRpt,publish.SectionId);
       Evaluate.EvaluateShift(nx,publish.SectionId);
    }
}

//this function1 again call another function where another foreach loop is running.

//Evaluate.Evaluateshift
Evaluateshift(shiftRpt rpt, int sectionId)
{
 ShiftPI currentShiftI = DataService.GetEntity(GetDataRequest<ShiftPI>.Create(c =>
                c.ShiftID == rpt.ShiftID && c.SectionPanelID == sectionId, "ShiftPI"));

    if(currentShiftI != null)
    {
      List<SectionPanelPI> sectionPanelPIs = DataService.GetAll(GetDataRequest<SectionPanelHSEKPI>.Create(c =>
                        c.SectionPanelID == sectionId, "PI", "PIStatistics")).ToList();


                foreach(sectionPanelPI in sectionPanelPIs)
                {
                 do more stuff....
                }
    }
}


public void function2(publish p1,nextshift nx, List<publish> pub)
{
    foreach(publish in pub.ToList())
    {
    //do stuff
    }
}

public void function3(publish p1,nextshift nx, List<publish> pub)
{
    foreach(publish in pub.ToList())
    {
    //do stuff
    }
}

public void function4(publish p1,nextshift nx, List<publish> pub)
{
    foreach(publish in pub.ToList())
    {
    //do stuff
    }
}

I guess your `//do stuff` modifies the collection like the exeption says. Provide more code. — t3chb0t, Dec 08 '14 at 12:22
I have edited my code I've seen in other post about giving copy of the list by adding .ToList() — dawncode, Dec 08 '14 at 12:47
...now look inside `do more stuff`. There is one more list `sectionPanelPIs`. Do you modify this one? — t3chb0t, Dec 08 '14 at 12:51
Is there another thread modifying `publishList` other than the ones we can see in your code? — Matthew Watson, Dec 08 '14 at 13:07
these four functions are inside the top foreach loop. but I assume when I put Task.WaitAll it will not go out for next value unless and until all task get completed.. — dawncode, Dec 08 '14 at 13:48
these four functions taking about 2 to 3 min each to complete the execution, that is why I want to execute them parallel. — dawncode, Dec 08 '14 at 17:18

score 0 · Answer 1 · edited May 23 '17 at 11:57

0

The problem is that you are modifying the collection during it's enumeration: you're trying to add or remove some values, or replace values with new ones. This is not allowed. As I don't have the code of your foreach a can't suggest a proper sulotuin, but you can check this question: Collection was modified; enumeration operation may not execute

edited May 23 '17 at 11:57

Community

1
1

answered Dec 08 '14 at 12:27

Vsevolod Goloviznin

12,074
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yes i knew about adding .ToList() to list it will create new copy for processing but still i'm getting the error. – dawncode Dec 08 '14 at 12:48

task parallel library not working with inner foreach loops

1 Answers1