Issue #12157: pool.map() does not handle empty iterable correctly
Initial patch by mouad
diff --git a/Lib/multiprocessing/pool.py b/Lib/multiprocessing/pool.py
index 0c29e64..ccee961 100644
--- a/Lib/multiprocessing/pool.py
+++ b/Lib/multiprocessing/pool.py
@@ -584,6 +584,7 @@
if chunksize <= 0:
self._number_left = 0
self._ready = True
+ del cache[self._job]
else:
self._number_left = length//chunksize + bool(length % chunksize)
diff --git a/Lib/test/test_multiprocessing.py b/Lib/test/test_multiprocessing.py
index 5f1bba3..0d98a14 100644
--- a/Lib/test/test_multiprocessing.py
+++ b/Lib/test/test_multiprocessing.py
@@ -1178,6 +1178,18 @@
join()
self.assertLess(join.elapsed, 0.5)
+ def test_empty_iterable(self):
+ # See Issue 12157
+ p = self.Pool(1)
+
+ self.assertEqual(p.map(sqr, []), [])
+ self.assertEqual(list(p.imap(sqr, [])), [])
+ self.assertEqual(list(p.imap_unordered(sqr, [])), [])
+ self.assertEqual(p.map_async(sqr, []).get(), [])
+
+ p.close()
+ p.join()
+
def raising():
raise KeyError("key")
@@ -2176,7 +2188,7 @@
'Queue', 'Lock', 'RLock', 'Semaphore', 'BoundedSemaphore',
'Condition', 'Event', 'Value', 'Array', 'RawValue',
'RawArray', 'current_process', 'active_children', 'Pipe',
- 'connection', 'JoinableQueue'
+ 'connection', 'JoinableQueue', 'Pool'
)))
testcases_processes = create_test_cases(ProcessesMixin, type='processes')
@@ -2190,7 +2202,7 @@
locals().update(get_attributes(manager, (
'Queue', 'Lock', 'RLock', 'Semaphore', 'BoundedSemaphore',
'Condition', 'Event', 'Value', 'Array', 'list', 'dict',
- 'Namespace', 'JoinableQueue'
+ 'Namespace', 'JoinableQueue', 'Pool'
)))
testcases_manager = create_test_cases(ManagerMixin, type='manager')
@@ -2204,7 +2216,7 @@
'Queue', 'Lock', 'RLock', 'Semaphore', 'BoundedSemaphore',
'Condition', 'Event', 'Value', 'Array', 'current_process',
'active_children', 'Pipe', 'connection', 'dict', 'list',
- 'Namespace', 'JoinableQueue'
+ 'Namespace', 'JoinableQueue', 'Pool'
)))
testcases_threads = create_test_cases(ThreadsMixin, type='threads')
diff --git a/Misc/NEWS b/Misc/NEWS
index 2890ebe..071e962 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -70,6 +70,9 @@
Library
-------
+- Issue #12157: Make pool.map() empty iterables correctly. Initial
+ patch by mouad.
+
- Issue #14992: os.makedirs(path, exist_ok=True) would raise an OSError
when the path existed and had the S_ISGID mode bit set when it was
not explicitly asked for. This is no longer an exception as mkdir