Merge to tip.
diff --git a/Lib/concurrent/futures/_base.py b/Lib/concurrent/futures/_base.py
index 79b91d4..6cfded3 100644
--- a/Lib/concurrent/futures/_base.py
+++ b/Lib/concurrent/futures/_base.py
@@ -536,15 +536,19 @@
fs = [self.submit(fn, *args) for args in zip(*iterables)]
- try:
- for future in fs:
- if timeout is None:
- yield future.result()
- else:
- yield future.result(end_time - time.time())
- finally:
- for future in fs:
- future.cancel()
+ # Yield must be hidden in closure so that the futures are submitted
+ # before the first iterator value is required.
+ def result_iterator():
+ try:
+ for future in fs:
+ if timeout is None:
+ yield future.result()
+ else:
+ yield future.result(end_time - time.time())
+ finally:
+ for future in fs:
+ future.cancel()
+ return result_iterator()
def shutdown(self, wait=True):
"""Clean-up the resources associated with the Executor.
diff --git a/Lib/test/test_concurrent_futures.py b/Lib/test/test_concurrent_futures.py
index 2662af7..ec84a66 100644
--- a/Lib/test/test_concurrent_futures.py
+++ b/Lib/test/test_concurrent_futures.py
@@ -369,7 +369,15 @@
class ThreadPoolExecutorTest(ThreadPoolMixin, ExecutorTest):
- pass
+ def test_map_submits_without_iteration(self):
+ """Tests verifying issue 11777."""
+ finished = []
+ def record_finished(n):
+ finished.append(n)
+
+ self.executor.map(record_finished, range(10))
+ self.executor.shutdown(wait=True)
+ self.assertCountEqual(finished, range(10))
class ProcessPoolExecutorTest(ProcessPoolMixin, ExecutorTest):