.Net Threading – BeginInvoke uses the thread pool

For a while now I’ve been curious as to whether the CLR uses the ThreadPool to execute a delegate when BeginInvoke is called:

private void InvokeFunc(Func<int> func)
{
    func.BeginInvoke(null, null); // does this execute on a threadpool thread?
}

Whilst common sense dictates that this must surely be true, I couldn’t be certain since I haven’t managed to find any confirmation in the documentations.

Thanks to Jon Skeet and Jeff Sternal who provided the answer to my question and a link to the MSDN article which confirms it:

If the BeginInvoke method is called, the common language runtime (CLR) queues the request and returns immediately to the caller. The target method is called asynchronously on a thread from the thread pool.

This of course, means that if your delegate is likely to take a while to execute you should not call BeginInvoke on the delegate to avoid blocking the ThreadPool threads, instead you could create a new thread or use a SmartThreadPool instance. I’ve discussed these aspect in more detail here and here if you’re interested.

References:

MSDN – Asynchronous Programming using Delegates

StackOverflow Question – Does Func.BeginInvoke use the ThreadPool

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Yan Cui

I’m an AWS Serverless Hero and the author of Production-Ready Serverless. I have run production workload at scale in AWS for nearly 10 years and I have been an architect or principal engineer with a variety of industries ranging from banking, e-commerce, sports streaming to mobile gaming. I currently work as an independent consultant focused on AWS and serverless.

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