Question

I am running into a bit of difficulty using the threadpool class and an array of ManualResetEvents. Below is a simple example of what I am doing. The problem is that in the DoWork method I am getting null references to the resetEvent[param as int] object.

Can’t seem to figure what I’m doing wrong.

(edit: got the code block working)

private static volatile ManualResetEvent[] resetEvents = new ManualResetEvent[NumThreads];
public void UpdateServerData()
{
   for (int i = 0; i < NumThreads ; i++)
        {
            resetEvents[i] = new ManualResetEvent(false);
            ThreadPool.QueueUserWorkItem(new WaitCallback(DoWork), (object) i);

        }
  WaitHandle.WaitAll(resetEvents);
}
private void DoWork(object param)
{
//do some random work
resetEvents[(int)param].Set();
}

EDIT: I have tried inserting a System.Threading.Thread.MemoryBarrier(); after each .Set() however i still get a null reference exception.

Answer 1

Pretty much I found the issue was in

for (int i = 0; i < NumThreads ; i++)    
{        
resetEvents[i] = new ManualResetEvent(false);        
ThreadPool.QueueUserWorkItem(new WaitCallback(DoWork), resetEvents[i]);    
}

Instead of declaring a new ManualResetEvent I simply called Reset(). The issue seemed to have been that that although I would use MemoryBarrier or locks, the physical memory wouldn’t be updated yet so it would point to null.