use explicit multiprocessing context for creating Pipe in subproc.py (#…

…1102)

tianshou/env/worker/subproc.py

@@ -3,7 +3,7 @@
 import time
 from collections import OrderedDict
 from collections.abc import Callable
-from multiprocessing import Pipe, connection
+from multiprocessing import connection
 from multiprocessing.context import BaseContext
 from typing import Any, Literal
 
@@ -149,11 +149,11 @@ def __init__(
         share_memory: bool = False,
         context: BaseContext | Literal["fork", "spawn"] | None = None,
     ) -> None:
-        self.parent_remote, self.child_remote = Pipe()
-        self.share_memory = share_memory
-        self.buffer: dict | tuple | ShArray | None = None
         if not isinstance(context, BaseContext):
             context = multiprocessing.get_context(context)
+        self.parent_remote, self.child_remote = context.Pipe()
+        self.share_memory = share_memory
+        self.buffer: dict | tuple | ShArray | None = None
         assert hasattr(context, "Process")  # for mypy
         if self.share_memory:
             dummy = env_fn()