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Let me start by saying that this is a nicely written class with good documentation. I also think that Nobody's answer provides some good advice, so mostly I'll build on that.

Let me start by saying that this is a nicely written class with good documentation. I also think that Nobody's answer provides some good advice, so mostly I'll build on that.

You document WorkQueue::WorkQueue, saying that numWorkers < 0 causes autodetection, but you autodetect whenever numWorkers < 1. That is, your documentation and implementation differ on behavior when numWorkers == 0.

(This is only a partial solution; you'll have to add a condition variable or similar to make sure that future calls to joinAll don't return before this one joins all its threads).

You document WorkQueue::WorkQueue, saying that numWorkers < 0 causes autodetection, but you autodetect whenever numWorkers < 1. That is, your documentation and implementation differ on behavior when numWorkers == 0.

I only have one correctness comment: you have problematic behavior in joinAll. If waitForCompletion and/or abort are called from multiple threads (and I can certainly imagine one thread calling waitForCompletion and another thread later calling abort), you have a race in joinAll; one thread may be mid-iteration when the other calls m_workers.clear().

I only have one correctness comment: you have problematic behavior in joinAll. If waitForCompletion and/or abort are called from multiple threads (and I can certainly imagine one thread calling waitForCompletion and another thread later calling abort), you have a race in joinAll; one thread may be mid-iteration when the other calls m_workers.clear(). Try the following:

void joinAll(){
 std::vector<std::thread> workers;
 {
 std::lock_guard<std::mutex> lg(m_mutex);
 workers = std::move(m_workers);
 }
 for (auto& thread : workers) {
 thread.join();
 }
}