def test_nthreads():
from datatable.internal import get_thread_ids
nthreads0 = dt.options.nthreads
curr_threads = get_thread_ids()
assert len(curr_threads) == nthreads0
for n in [4, 1, nthreads0 + 10, nthreads0]:
dt.options.nthreads = n
new_threads = get_thread_ids()
assert len(new_threads) == n
m = min(len(curr_threads), len(new_threads))
assert curr_threads[:m] == new_threads[:m]
curr_threads = new_threads
assert dt.options.nthreads == nthreads0
def test_multiprocessing_threadpool():
# Verify that threads work properly after forking (#1758)
import multiprocessing as mp
from datatable.internal import get_thread_ids
parent_threads = get_thread_ids()
n = 4
with mp.Pool(processes=n) as pool:
child_threads = pool.starmap(get_thread_ids, [()] * n, chunksize=1)
assert len(child_threads) == n
for chthreads in child_threads:
assert len(parent_threads) == len(chthreads)
