I really have to agree with sundialsvc4. Threads are so expensive to create that you are almost aways much better off to create a set number of threads (usually no more than the physical number of cores you have, for optimal results), then using a queuing system, such as Thread::Queue, to distribute work until all the work is complete.

Also, unless you are creating a thread that is performing a never ending task (such as listening to events from an external source), its generally not a great idea to detach them, especially if you are interested in when they complete or what they return.