When All Threads Are Complete

Question

This is my first real attempt at using multithreading, I want to know how I can tell when all of my tasks groups are done running:

for (int i = 0; i < taskGroups.Count(); i++) {
    ThreadStart t = delegate { RunThread(taskGroups[i]); };
    new Thread(t).Start();
}
if(allThreadsComplete){ //???

}

Any help would be much appreciated

Addendum:

ThreadStart[] threads = new ThreadStart[taskGroups.Count()];
for (int i = 0; i < taskGroups.Count(); i++) {
    threads[i] = new ThreadStart[]
    threads[i] = delegate { RunThread(taskGroups[i]); };
    new Thread(t).Start();
}
bool threadsComplete = false;
while(!threadsComplete){
    for(int i=0;i<taskGroups.Count();i++){
        if(threads[i].State == complete)
        threadsComplete = true;
    }
}

Answer 1

You need to store all your threads, and then call Thread.Join().

Something like this:

List<Thread> threads = new List<Thread>();
for (int i = 0; i < taskGroups.Count(); i++) {
   int temp = i; //This fixes the issue with i being shared
   Thread thread = new Thread(() => RunThread(taskGroups[temp]));
   threads.Add(thread);
   thread.Start();
}

foreach (var thread in threads) {
    thread.Join();
}