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POParallel ForEach confusion .Net C#
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  1. POParallel ForEach confusion .Net C#
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    copied!<p>I have some code running in my application that calls the method below for multiple students.</p> <p>The problem is that I use the Student parallel index variable to call another method and using the local variable of that method I insert a message record and save all messages for that Student once. </p> <p>What happens is sometimes the message inserted into the database has the wrong ownerId sometimes. </p> <p>For example a message owned by StudentRecord Id 10 is inserted into the DB with owner Id value set as 17 instead of 10. 17 is a studentId in the same class but so it seems to be getting confused with the parallel loop. </p> <p>For my understanding of the parallel loop everything inside the loop will have its own instance of a local variable so index Student will create its own block of local variables so I don't see how the StudentId is being inserted incorrectly into the Database. </p> <p>Some bad sharing must be going on. This is not the actual data or variables used. I just tried to simplify as much as possible. </p> <pre><code>var students = GetAllStudentsForThisClass(); Parallel.ForEach( students, new ParallelOptions { MaxDegreeOfParallelism = 5 }, student =&gt; { var dbThread = new StudentLifeRepository(); var studentRecord = dbThread.GetStudentById(student.Id); var records = new List&lt;Student_Messages&gt;(); do { StudentMessage.Statuses = //web api call, returns null when no Statuses are available from api foreach (var studentMessage in StudentMessage.Statuses) { var message = new Student_Messages(); //this is where I think the problem lies message.ownerId = studentRecord.StudentId; message.CreatedDate = studentMessage.MessageDate; message.ID = studentMessage.MessageId; message.message = studentMessage.message; records.Add(studentMessage); } //this loop happens until No more messages are available for this student } while(StudentMessage.Statuses != null); //DistinctItemComparer is making sure All messageIds //are unique since that is used for primary key foreach (var pt in records.Distinct(new DistinctItemComparer())) { dbThread.Add(pt); dbThread.Save(); } } ); //close of parallel loop </code></pre>
 

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