Make sure that main thread run on it's own core alone

I have a main thread which do some not-so-heavy-heavy work and also I'm creating worker threads which do very-heavy work. All documentation and examples shows how to create a number of hardware threads equal to std::thread::hardware_concurrency(). But since main thread already existed the number of threads becomes std::thread::hardware_concurrency() + 1. For example:

• my machine supports 2 hardware threads.
• in main thread I'm creating this 2 threads and the total number of threads becomes 3.
• a core with the main thread do it's job plus (probably) the worker job.

Of course I don't want this because UI (which is done in main thread) becomes not responsive due to latency. What will happen if I create std::thread::hardware_concurrency() - 1 thread? Will it guarantee that the main thread and only main thread is running on single core? How can I check it?

P.S.: I'm using some sort of pool - I start threads on the program start and stop on exit. During the execution all worker threads run infinite while loop.