Demos

fork_map.wpr

@@ -4,6 +4,16 @@
 # Wing project file                                              #
 ##################################################################
 [project attributes]
+console.toolbox = [{'autosave': False,
+                    'id': 'cmd-JWEPUsuAbCaNufpa',
+                    'io_encoding': None,
+                    'key_binding': None,
+                    'line_mode': True,
+                    'loc': '/home/rutherford/code/fork_map/fork_map/demos/fork.py',
+                    'pseudo_tty': False,
+                    'raise_panel': True,
+                    'shared': False,
+                    'title': None}]
 proj.directory-list = [{'dirloc': loc('fork_map'),
                         'excludes': (),
                         'filter': '*',

fork_map/demos/deadlock.py

@@ -0,0 +1,23 @@
+"""The below code causes a deadlock on python <3.14"""
+
+import os
+import time
+from concurrent.futures import ProcessPoolExecutor
+import threading
+
+lock = threading.Lock()
+
+
+def process_items(name):
+    print(f"{name}: acquiring lock")
+    with lock:
+        print(f"{name}: has lock")
+        time.sleep(0.1)
+    print(f"{name}: released lock")
+
+
+t = threading.Thread(target=process_items, args=("Thread",))
+t.start()
+
+with ProcessPoolExecutor() as e:
+    e.submit(process_items, "Process")

fork_map/demos/demo.py

@@ -0,0 +1,25 @@
+import os
+
+# Todo fix import paths
+from fork_map.fork_map import fork_map
+
+result = fork_map(lambda x: x * 2, range(5))
+print(result)
+
+## -----------------------------------
+
+from multiprocessing.pool import Pool
+
+# This fails, as lambdas aren't pickleable.
+# with Pool() as p:
+# result = p.map(lambda x: x * 2, range(5))
+
+# print(result)
+
+
+# ----
+
+LETTERS = "abcde"
+
+for r in fork_map(lambda idx: f"{os.getpid()} got letter {LETTERS[idx]}", [0, 1, 3]):
+    print(r)

fork_map/demos/fork.py

@@ -0,0 +1,7 @@
+import os
+
+pid = os.fork()
+if pid:
+    print('I am the parent')
+else:
+    print('I am the child')

fork_map/demos/fork_vs_spawn.py

@@ -0,0 +1,19 @@
+"""The below fails unless start method is fork"""
+
+import os
+import multiprocessing
+from concurrent.futures import ProcessPoolExecutor
+
+
+def get_letter(idx: int) -> str:
+    pid = os.getpid()
+    return f"{pid=} got letter {LETTERS[idx]}"
+
+
+if __name__ == "__main__":
+    multiprocessing.set_start_method("spawn")
+    LETTERS = "abcde"
+
+    with ProcessPoolExecutor() as e:
+        for r in e.map(get_letter, [0, 1, 3]):
+            print(r)

fork_map/fork_map.py

@@ -43,12 +43,13 @@ def _process_in_fork(
     try:
         r = func(*args, **kwargs)
 
-        # pickle here, so that we can't crash with pickle errors in the finally clause
+        # pickle here, so that we can't crash with pickle errors in the finally clause.
         pickled_r = pickle.dumps(r)
         result = make_result(result=pickled_r)
     except Exception as e:
         try:
-            # In case func does something stupid like raising an unpicklable exception
+            # In case func does something untoward like raising an unpicklable
+            # exception.
             pickled_exception = pickle.dumps(e)
         except AttributeError:
             pickled_exception = pickle.dumps(