def test_get_context_using_python3_posix():
""" get_context() respects configuration.
If default context is changed this test will need to change too.
"""
assert get_context() is multiprocessing.get_context(None)
with dask.config.set({"multiprocessing.context": "forkserver"}):
assert get_context() is multiprocessing.get_context("forkserver")
with dask.config.set({"multiprocessing.context": "spawn"}):
assert get_context() is multiprocessing.get_context("spawn")
def test_get_context_using_python3_posix():
""" get_context() respects configuration.
If default context is changed this test will need to change too.
"""
assert get_context() is multiprocessing.get_context(None)
with dask.config.set({"multiprocessing.context": "forkserver"}):
assert get_context() is multiprocessing.get_context("forkserver")
with dask.config.set({"multiprocessing.context": "spawn"}):
assert get_context() is multiprocessing.get_context("spawn")
def test_register_backend_entrypoint(tmp_path):
# Create special sizeof implementation for a dummy class
(tmp_path / "impl_sizeof.py").write_bytes(
b"def sizeof_plugin(sizeof):\n"
b' print("REG")\n'
b' @sizeof.register_lazy("class_impl")\n'
b" def register_impl():\n"
b" import class_impl\n"
b" @sizeof.register(class_impl.Impl)\n"
b" def sizeof_impl(obj):\n"
b" return obj.size \n"
)
# Define dummy class that possesses a size attribute
(tmp_path / "class_impl.py").write_bytes(
b"class Impl:\n def __init__(self, size):\n self.size = size"
)
dist_info = tmp_path / "impl_sizeof-0.0.0.dist-info"
dist_info.mkdir()
(dist_info / "entry_points.txt").write_bytes(
b"[dask.sizeof]\nimpl = impl_sizeof:sizeof_plugin\n"
)
with get_context().Pool(1) as pool:
assert (
pool.apply(_get_sizeof_on_path, args=(tmp_path, 3_14159265)) == 3_14159265
)
pool.join()
def start(self) -> Iterator:
"""Context manager for initializing execution."""
# import dask here to reduce prefect import times
import dask.config
from dask.callbacks import Callback
from dask.system import CPU_COUNT
class PrefectCallback(Callback):
def __init__(self): # type: ignore
self.cache = {}
def _start(self, dsk): # type: ignore
overlap = set(dsk) & set(self.cache)
for key in overlap:
dsk[key] = self.cache[key]
def _posttask(self, key, value, dsk, state, id): # type: ignore
self.cache[key] = value
with PrefectCallback(), dask.config.set(**self.dask_config):
if self.scheduler == "synchronous":
self._pool = None
else:
num_workers = dask.config.get("num_workers", None) or CPU_COUNT
if self.scheduler == "threads":
from multiprocessing.pool import ThreadPool
self._pool = ThreadPool(num_workers)
else:
from dask.multiprocessing import get_context
context = get_context()
self._pool = context.Pool(
num_workers, initializer=_multiprocessing_pool_initializer
)
try:
exiting_early = False
yield
except BaseException:
exiting_early = True
raise
finally:
if self._pool is not None:
if exiting_early:
self._interrupt_pool()
else:
self._pool.close()
self._pool.join()
self._pool = None
def test_get_context_always_default():
""" On Python 2/Windows, get_context() always returns same context."""
assert get_context() is multiprocessing
with pytest.warns(UserWarning):
with dask.config.set({"multiprocessing.context": "forkserver"}):
assert get_context() is multiprocessing
def test_get_context_always_default():
""" On Python 2/Windows, get_context() always returns same context."""
assert get_context() is multiprocessing
with pytest.warns(UserWarning):
with dask.config.set({"multiprocessing.context": "forkserver"}):
assert get_context() is multiprocessing
