Will the list of tasks being cleared after await Tasks.WhenAll(tasks)?

Question

Hi,

Will the list of tasks being cleared after await Tasks.WhenAll(tasks)?

int i=0;
List<Task> tasks = new List<Task>();

do
{
     tasks.Add(Do_Test1(i));
     tasks
     tasks
     tasks
     tasks

     await Task.WhenAll(tasks);

     // Do I need to call tasks.Clear(); here?
}

Answer 1

Hello @Dondon510 ,

Thanks for reaching out

To clarify your question:

• The List<Task> is not automatically cleared after await Task.WhenAll(tasks).
• Task.WhenAll(tasks) simply waits for all the tasks in the list to complete. It does not modify the list itself. The list will still contain references to the completed tasks after the await.
• If you're inside a loop and reusing the same List<Task> instance, you should call tasks.Clear() after Task.WhenAll() to avoid accumulating completed tasks. This helps prevent unnecessary memory usage and ensures you're only waiting on fresh tasks in each iteration.

Here’s the corrected version:

int i = 0;
List<Task> tasks = new List<Task>();
 
do
{
    tasks.Add(Do_Test1(i));
    // Add other tasks as needed
    // tasks.Add(Do_Test2(i));
    // tasks.Add(Do_Test3(i));
 
    await Task.WhenAll(tasks);
 
    tasks.Clear(); // Clear the list for the next iteration
 
    i++; // Optional: increment i if needed
}
while (someCondition); // Add your loop condition

Final thoughts:

Task.WhenAll() does not clear the list.

You should clear the list manually if you're reusing it.

Hope my answer would help.

Answer 2

the list tasks will clear when the list is garbage collected. you don't show usage, but if you have no other references, the list will be released when it goes out of scope.

but if this code was in main, it would not leave scope and never get cleared (program exit does not do a garbage collect).