ignored internal deprecation warning in multiprocessing

pyproject.toml

@@ -84,6 +84,8 @@ filterwarnings = """
     error
     ignore:numpy.ufunc size changed
     ignore:The explicit passing of coroutine objects to asyncio.wait()
+    ignore::DeprecationWarning:multiprocessing.reduction
+
 """
 # Doctest python code in docs, python code in src docstrings, test functions in tests
 testpaths = "docs src tests"

tests/fixtures/mocked_panda.py

@@ -7,7 +7,7 @@
 from io import BufferedReader
 from itertools import chain, repeat
 from logging import handlers
-from multiprocessing import Queue, get_context
+from multiprocessing import Queue, get_context, set_start_method
 from multiprocessing.connection import Connection
 from pathlib import Path
 from typing import Any, Optional, TypeVar
@@ -250,7 +250,12 @@ def get_multiprocessing_context():
         start_method = "spawn"
     else:
         start_method = "forkserver"
-    return get_context(start_method)
+
+    set_start_method(start_method, force=True)
+    return get_context()
+
+
+MULTIPROCESSING_CONTEXT = get_multiprocessing_context()
 
 
 def enable_codecov_multiprocess():
@@ -318,8 +323,7 @@ def caplog_workaround():
 
     @contextmanager
     def ctx() -> Generator[None, None, None]:
-        ctx = get_multiprocessing_context()
-        logger_queue = ctx.Queue()
+        logger_queue = MULTIPROCESSING_CONTEXT.Queue()
         logger = logging.getLogger()
         logger.addHandler(handlers.QueueHandler(logger_queue))
         yield

tests/test_hdf_ioc.py

@@ -27,13 +27,13 @@
 from softioc import asyncio_dispatcher, builder, softioc
 
 from fixtures.mocked_panda import (
+    MULTIPROCESSING_CONTEXT,
     TIMEOUT,
     MockedAsyncioClient,
     Rows,
     append_random_uppercase,
     custom_logger,
     enable_codecov_multiprocess,
-    get_multiprocessing_context,
     select_and_recv,
 )
 from pandablocks_ioc._hdf_ioc import (
@@ -278,9 +278,8 @@ def hdf5_subprocess_ioc_no_logging_check(
 
     test_prefix, hdf5_test_prefix = new_random_hdf5_prefix
 
-    ctx = get_multiprocessing_context()
-    parent_conn, child_conn = ctx.Pipe()
-    p = ctx.Process(
+    parent_conn, child_conn = MULTIPROCESSING_CONTEXT.Pipe()
+    p = MULTIPROCESSING_CONTEXT.Process(
         target=subprocess_func, args=(test_prefix, standard_responses, child_conn)
     )
     try:
@@ -307,9 +306,8 @@ def hdf5_subprocess_ioc(
 
     with caplog.at_level(logging.WARNING):
         with caplog_workaround():
-            ctx = get_multiprocessing_context()
-            parent_conn, child_conn = ctx.Pipe()
-            p = ctx.Process(
+            parent_conn, child_conn = MULTIPROCESSING_CONTEXT.Pipe()
+            p = MULTIPROCESSING_CONTEXT.Process(
                 target=subprocess_func,
                 args=(test_prefix, standard_responses, child_conn),
             )