multithreading while blocking main thread

Question

How do I start 2 or more threads all at once and block the main thread until the others threads are complete?

Answer 1

From the main thread, call Thread.Join on each of the other threads.

(EDIT: Now you've specified C#, there's no need for the platform agnostic comment.)

For example:

Thread t1 = new Thread(FirstMethod).Start();
Thread t2 = new Thread(SecondMethod).Start();

t1.Join();
t2.Join();

It doesn't matter what order you call Join in, if you only want to wait until they've all finished. (If you want to continue when any of them have finished, you need to get into the realm of wait handles.)