Fix bug in Python 3.8 on Mac

bettermap/bettermap.py

@@ -7,13 +7,18 @@
 import itertools
 import multiprocessing as mp
 import multiprocessing.connection
+from multiprocessing.context import ForkProcess
 from typing import Iterable, List, Optional, Any, Dict
 
 import dill
 
 from queue import Queue
 from threading import Thread
 
+
+mpctx = mp.get_context("fork")
+
+
 def threaded_generator(g, maxsize: int = 16):
     q = Queue(maxsize=maxsize)
 
@@ -55,7 +60,7 @@ def map_per_process(
     input_sequence: Iterable,
     *,
     serialization_items: Optional[List[Any]] = None,
-    parallelism: int = mp.cpu_count()
+    parallelism: int = mpctx.cpu_count()
 ) -> Iterable:
     if serialization_items is not None and len(serialization_items) > 0:
         serialization_ids = [id(o) for o in serialization_items]
@@ -82,7 +87,7 @@ def unpickle(b: bytes) -> Any:
             return unpickler.load()
 
     pipeno_to_pipe: Dict[int, multiprocessing.connection.Connection] = {}
-    pipeno_to_process: Dict[int, mp.Process] = {}
+    pipeno_to_process: Dict[int, ForkProcess] = {}
 
     def process_one_item(send_pipe: multiprocessing.connection.Connection, item):
         try:
@@ -114,8 +119,8 @@ def yield_from_pipes(pipes: List[multiprocessing.connection.Connection]):
 
     try:
         for item in input_sequence:
-            receive_pipe, send_pipe = mp.Pipe(duplex=False)
-            process = mp.Process(target=process_one_item, args=(send_pipe, item))
+            receive_pipe, send_pipe = mpctx.Pipe(duplex=False)
+            process = mpctx.Process(target=process_one_item, args=(send_pipe, item))
             pipeno_to_pipe[receive_pipe.fileno()] = receive_pipe
             pipeno_to_process[receive_pipe.fileno()] = process
             process.start()
@@ -173,7 +178,7 @@ def ordered_map_per_thread(
     fn,
     input_sequence: Iterable,
     *,
-    parallelism: int = mp.cpu_count()
+    parallelism: int = mpctx.cpu_count()
 ) -> Iterable:
     executor = ThreadPoolExecutor(max_workers=parallelism)
     input_sequence = (executor.submit(fn, item) for item in input_sequence)