How do you wait for several threads to complete execution?

Using a CountdownEvent object is an effective way to wait for several threads to complete execution because it allows you to set a count that represents the number of threads that you are waiting on. When each thread completes its work, it signals the CountdownEvent object, decrementing the count. Once the count reaches zero, any thread that is waiting on that CountdownEvent can proceed.

This approach is particularly useful in scenarios where you know the exact number of threads you are working with and need to ensure that all of them have completed before moving on to the next step in your program. By using CountingEvent, you avoid manual management of thread signaling, which can become complex and error-prone.

The other options, while related to thread synchronization, are designed for different use cases. For example, a ManualResetEvent allows a thread to signal one or more waiting threads but does not manage a count of how many threads have completed. A Semaphore is typically used to control access to a shared resource by a limited number of threads and is not specialized for waiting for completion of multiple threads. Meanwhile, a Mutex is mainly for exclusive access to a resource and does not provide a mechanism for waiting for multiple threads to finish execution.