Question

If I do something like class myclass : public somelibrary::thread

1. Are all methods called on myclass executed in their own thread?
2. Is only run() executed in its own thread?
3. For every method to be executed in its own thread, do I have to create a new thread in each method?

Answer 1

If I do something like class myclass : public somelibrary::thread
does this mean that all methods called on myclass will be called in
their own thread?

Not necessarily. It depends on the design of somelibrary::thread. In fact, Boost.Thread is not used this way (via inheritance). In that case, you simply create a new boost::thread object passing in a callable object (functors, function pointers, etc.) into its constructor.

However, I haven’t seen any thread library where calling any method on a class derived from somelibrary::thread spawns a new thread. That is asking for data races, unless everything is somehow synchronized. But then your code would be wasting a lot of time waiting on synchronization primitives. Not to mention that threads are relatively expensive in terms of operating system resources. An application may have at most several threads running at any one time assuming it wasn’t designed by an idiot. Methods on the other hand may be called many, many times during the application running time.

Is the only thing run in it’s own thread in the “run” method of such
thread?

Not all thread libraries call a run() method when running a new thread. For example in Boost.Thread, the entry point is operator()(). But yes, the entry point runs in its own thread, separate from the calling thread. All methods called by run(), directly or indirectly, runs in the newly-spawned thread.

If only the run method is executed in it’s own thread, what if I want
every method to be called in it’s own thread instead of just that one?

This is almost certainly not what you actually want in C++, because of the fact that threads are very expensive in terms of operating system resources. You’ll be making your operating system waste time allocating and destroying threads all the time. Even in languages like Erlang, where threads are extremely cheap compared to OS threads, you don’t typically spawn a new thread for every single method. A program running many threads or constantly creating/destroying threads is a sign of a badly-designed program.

Do I have to create a new thread in each method?

Yes, if you want each method to run in its own thread, but again, you almost certainly don’t want this.