Question

I need some advice on multithreading.

Example: I want to spawn 200 Threads, each one should grab one different image from an website (the site is kinda slow). But there should be max. 40 Threads at once.

Any idea?

I look forward to some answers.

Answer 1

You can easily use ThreadPool for this. The pool does a good job of managing threads but if you really really must limit the maximum number you can use:

ThreadPool.SetMaxThreads(40, 40);

// submit 200 tasks to the pool
for(int i = 0; i < 200; i++)
{
   ThreadPool.QueueUserWorkItem(
       () =>
       {
           // code for each task
       });
}

Unfortunately, there is no built-in way to wait for the tasks to finish so you’ll just have to improvise something. If you have access to .NET 4.0 you can check out Parallel.For:

ParallelOptions po = new ParallelOptions();
po.MaxDegreeOfParallelism = 40;
Parallel.For(0, 200, po,
   i =>
   {
      // code for each task
   });