For the main node / wallet the number of threads are controlled (and always have been) in the config.txt file (thread_limit=)
For the default miner the number of threads is also controlled in config.txt file (mining_threads=)
For the optihash miner the number of threads in controlled in miner.txt (mining_threads=)

I don't know how threads are controlled in the closed source acc-pool miner (I assume command line)