Function blosc2_set_nthreads 

pub unsafe extern "C" fn blosc2_set_nthreads(nthreads: i16) -> i16

@brief Initialize a pool of threads for compression/decompression. If @p nthreads is 1, then the serial version is chosen and a possible previous existing pool is ended. If this is not called, @p nthreads is set to 1 internally.

@param nthreads The number of threads to use.

@return The previous number of threads.