C# Cookbook

15.10. Waiting for All Threads in theThread Pool to Finish

Problem

For threads that are manually created via the Thread class, you can call the Join method to wait for a thread to finish. This works well when you need to wait for all threads to finish processing before an application terminates. Unfortunately, the thread pool threads do not have a Join method. You need to make sure that all threads in the thread pool have finished processing before another thread terminates or your application’s main thread terminates.

Solution

Use a combination of the ThreadPool methods—GetMaxThreads and GetAvailableThreads—to determine when the ThreadPool is finished processing the requests:

public static void Main( ) { for(int i=0;i<25;i++) { // have to wait or threadpool never gives out threads to requests Thread.Sleep(50); // queue thread request ThreadPool.QueueUserWorkItem(new WaitCallback(ThreadProc),i); } // have to wait here or the background threads in the thread // pool would not run before the main thread exits. Console.WriteLine("Main Thread waiting to complete..."); bool working = true; int workerThreads = 0; int completionPortThreads = 0; int maxWorkerThreads = 0; int maxCompletionPortThreads = 0; // get max threads in the pool ThreadPool.GetMaxThreads(out maxWorkerThreads,out maxCompletionPortThreads); while(working) { // get available threads ThreadPool.GetAvailableThreads(out workerThreads,out completionPortThreads); if(workerThreads == maxWorkerThreads) { // allow to quit working ...