gh-139462: Make the ProcessPoolExecutor BrokenProcessPool exception report which child process terminated

Lib/concurrent/futures/process.py

@@ -477,6 +477,15 @@ def _terminate_broken(self, cause):
         if cause is not None:
             bpe.__cause__ = _RemoteTraceback(
                 f"\n'''\n{''.join(cause)}'''")
+        else:
+            # No cause known, so try to report some helpful info about
+            # which process(es) terminated and with what exit code
+            errors = []
+            for p in self.processes.values():
+                if p.exitcode:  # Report any nonzero exit codes
+                    errors.append(f"Process {p.pid} terminated abruptly with exit code {p.exitcode}")
+            if errors:
+                bpe.__cause__ = _RemoteTraceback("\n".join(errors))
 
         # Mark pending tasks as failed.
         for work_id, work_item in self.pending_work_items.items():

Lib/test/test_concurrent_futures/test_process_pool.py

@@ -1,3 +1,4 @@
+import ctypes
 import os
 import queue
 import sys
@@ -106,6 +107,23 @@ def test_traceback(self):
         self.assertIn('raise RuntimeError(123) # some comment',
                       f1.getvalue())
 
+    @staticmethod
+    def _segfault():
+        ctypes.string_at(0)
+
+    def test_traceback_when_child_process_segfaults(self):
+        # gh-139462 enhancement - BrokenProcessPool exceptions
+        # should describe which process terminated.
+        future = self.executor.submit(self._segfault)
+        with self.assertRaises(Exception) as cm:
+            future.result()
+
+        bpe = cm.exception
+        self.assertIs(type(bpe), BrokenProcessPool)
+        cause = bpe.__cause__
+        self.assertIs(type(cause), futures.process._RemoteTraceback)
+        self.assertIn("terminated abruptly with exit code", cause.tb)
+
     @warnings_helper.ignore_fork_in_thread_deprecation_warnings()
     @hashlib_helper.requires_hashdigest('md5')
     def test_ressources_gced_in_workers(self):