From 5d408c0bb679f916f8bf600528293752d0007f76 Mon Sep 17 00:00:00 2001
From: Adrian Seyboldt <adrian.seyboldt@gmail.com>
Date: Mon, 6 Jul 2020 17:51:10 +0200
Subject: [PATCH] Use mp_ctx forkserver on MacOS

---
 pymc3/__init__.py          | 6 ------
 pymc3/parallel_sampling.py | 4 ++++
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/pymc3/__init__.py b/pymc3/__init__.py
index 21ec7f3a591..ad47bbbfe28 100644
--- a/pymc3/__init__.py
+++ b/pymc3/__init__.py
@@ -27,12 +27,6 @@
         handler = logging.StreamHandler()
         _log.addHandler(handler)
 
-# Set start method to forkserver for MacOS to enable multiprocessing
-# Closes issue https://github.com/pymc-devs/pymc3/issues/3849
-sys = platform.system()
-if sys == "Darwin":
-    new_context = mp.get_context("forkserver")
-
 
 def __set_compiler_flags():
     # Workarounds for Theano compiler problems on various platforms
diff --git a/pymc3/parallel_sampling.py b/pymc3/parallel_sampling.py
index 84f2f88f79e..fb4b464b01c 100644
--- a/pymc3/parallel_sampling.py
+++ b/pymc3/parallel_sampling.py
@@ -20,6 +20,7 @@
 import pickle
 from collections import namedtuple
 import traceback
+import platform
 from pymc3.exceptions import SamplingError
 
 import numpy as np
@@ -420,6 +421,9 @@ def __init__(
             raise ValueError("Number of seeds and start_points must be %s." % chains)
 
         if mp_ctx is None or isinstance(mp_ctx, str):
+            # Closes issue https://github.com/pymc-devs/pymc3/issues/3849
+            if platform.system() == 'Darwin':
+                mp_ctx = "forkserver"
             mp_ctx = multiprocessing.get_context(mp_ctx)
 
         step_method_pickled = None