[3.12] gh-94777: Fix deadlock in ProcessPoolExecutor (GH-94784) (#106609)

gh-94777: Fix deadlock in ProcessPoolExecutor (GH-94784)

Fixes a hang in multiprocessing process pool executor when a child process crashes and code could otherwise block on writing to the pipe.  See GH-94777 for more details.
(cherry picked from commit 6782fc050281205734700a1c3e13b123961ed15b)

Co-authored-by: Louis Paulot <55740424+lpaulot@users.noreply.github.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/Lib/test/test_concurrent_futures.py b/Lib/test/test_concurrent_futures.py
index a20cb84..39dbe23 100644
--- a/Lib/test/test_concurrent_futures.py
+++ b/Lib/test/test_concurrent_futures.py
@@ -1172,6 +1172,11 @@ def _crash(delay=None):
     faulthandler._sigsegv()
 
 
+def _crash_with_data(data):
+    """Induces a segfault with dummy data in input."""
+    _crash()
+
+
 def _exit():
     """Induces a sys exit with exitcode 1."""
     sys.exit(1)
@@ -1371,6 +1376,19 @@ class ExecutorDeadlockTest:
         # dangling threads
         executor_manager.join()
 
+    def test_crash_big_data(self):
+        # Test that there is a clean exception instad of a deadlock when a
+        # child process crashes while some data is being written into the
+        # queue.
+        # https://github.com/python/cpython/issues/94777
+        self.executor.shutdown(wait=True)
+        data = "a" * support.PIPE_MAX_SIZE
+        with self.executor_type(max_workers=2,
+                                mp_context=self.get_context()) as executor:
+            self.executor = executor  # Allow clean up in fail_on_deadlock
+            with self.assertRaises(BrokenProcessPool):
+                list(executor.map(_crash_with_data, [data] * 10))
+
 
 create_executor_tests(ExecutorDeadlockTest,
                       executor_mixins=(ProcessPoolForkMixin,