How to stop one thread until n threads have completed their work

Question

I have an application with one main thread and N worker threads. At some point I need that the main thread waits until all the N threads have completed one section of their work.

I normally would use Monitor.Wait() and Monitor.Pulse() but this will prevent the N threads from working at the same time.

Any idea on how to do that?

Thanks in advance.

Answer 1

Ok, what I'm doing now (using your ideas) and seems to work is this:

I declared a list of ManualResetEvent:

Private m_waitHandles As List(Of Threading.ManualResetEvent)

The process accepts incoming Tcp connections and starts one thread on each connection. So at the new client handler I've added this code:

Dim waitHandle As Threading.ManualResetEvent
waitHandle = New Threading.ManualResetEvent(True)
SyncLock (DirectCast(m_waitHandles, IList).SyncRoot)
    m_waitHandles.Add(waitHandle)
End SyncLock

''# Do all the work
StoppableMethod()

SyncLock (DirectCast(m_waitHandles, IList).SyncRoot)
    waitHandle = m_waitHandles.Item(Threading.WaitHandle.WaitAny(m_waitHandles.ToArray()))
End SyncLock

waitHandle.Reset()
NonStoppableMethod()
waitHandle.Set()

SyncLock (DirectCast(m_waitHandles, IList).SyncRoot)
    m_waitHandles.Remove(waitHandle)
End SyncLock

The last thing done is to modify the Stop method to be sure that the Stop operation will not done with any thread inside the NonStoppableMethod:

SyncLock (DirectCast(m_waitHandles, IList).SyncRoot)
    If m_waitHandles.Count > 0 Then
        Threading.WaitHandle.WaitAll(m_waitHandles.ToArray())
    End If
End SyncLock

I'm not sure that this is done in a right way because it's the first time I deal with things like that. Do you feel that this is ok and is a good approach?

Thanks to all, mates!