Passing lists into a Task

c#, c#-4.0, multithreading, task-parallel-library

Solution

You've got a closure bug.

The lambda `() => WriteToDB(new List<MyType>(list))` isn't executed until the new `Task` starts. This will sometimes be after your call to `list.Clear()`.

The fix is to capture the copy of the list outside the lambda:

var chunk = new List<MyType>(list);
Task.Factory.StartNew(() => WriteToDB(chunk));

list.Clear();

Problem

I am a newbie to C# and Threading and this is a very simple question, but has me really stuck. I did search on this site but could not find an answer similar to my scenario: I have a method say Parent() and in that I create a typed list, every nth time I pass it off to a Task. I have the problem of when to clear the list and release the memory since it keeps growing. I tried clearing list at the end of the task, if I clear list with the Parent method, the list is empty in the thread. Could someone help me? I know this is a very simple problem, but would appreciate the help. ``` public void Parent() { List<MyType> list = new List<MyType>(); for (int i = 0; i< N; i++) { list.Add(new MyType {Var = "blah"}); if ( i% 10 == 0) //every tentth time we send a task out tou a thread { Task.Factory.StartNew(() => WriteToDB(new List<MyType>(list))); //here I am sending a new instance of the list //Task.Factory.StartNew(() => WriteToDB((list))); //here I am sending same instance list.Clear(); //if I clear here the list sent to the WriteToDB is empty //if I do not, the memory keeps growing up and crashes the app } private void WriteToDB(List<MyType> list) { //do some calculations with the list //insert into db list.Clear(); } } } ```

Original source