warn if an exception leaves the run-context

This commit adds a warning that describes the possibility
of a stall, if an exception leaves the run-context.

The reason for the possible stall is that it is not clear
whether the code in the run-context did trigger a
subprocess exit. If it did not, and if no timeouts are
set, the exit handler of the run-context might wait
indefinitely for the subprocess to exit.

If the code ensures that all exceptions are caught, e.g.
by using a try-finally clause, and the subprocess exit
is triggered in case of an exception, the stalling
can be prevented.

datalad_next/runners/run.py

@@ -4,6 +4,7 @@
 """
 from __future__ import annotations
 
+import logging
 import subprocess
 from collections.abc import Generator
 from contextlib import contextmanager
@@ -23,6 +24,9 @@
 )
 
 
+lgr = logging.getLogger('datalad.ext.next.runners.run')
+
+
 def _create_kill_wrapper(cls: type[Protocol]) -> type[Protocol]:
     """ Extend ``cls`` to supports the "kill-interface"
 
@@ -252,6 +256,16 @@ def run(
     else:
         try:
             yield KillingResultGenerator(result)
+        except:
+            import sys, time
+            e = sys.exc_info()[1]
+            lgr.warning(
+                f'Possible stall: exception ({e!r}) raised in '
+                f'run-context ({cmd!r}), waiting for subprocess exit. If the '
+                f'subprocess exit was not triggered yet, and if no termination-'
+                f' or kill-timeout is active, this might wait forever.'
+            )
+            raise
         finally:
             # Arm the protocol, that will enable terminate signaling or kill
             # signaling, if terminate_time or kill_time are not None.

datalad_next/runners/tests/test_run.py

@@ -378,3 +378,22 @@ def test_run_nongenerator():
         assert res['code'] == 0
         assert res['stdout'] == 'outy'
         assert res['stderr'] == 'error'
+
+
+def test_run_exception_in_context(monkeypatch):
+    # Check that an exception in the context is logged and re-raises:
+    warnings = []
+    monkeypatch.setattr(
+        'datalad_next.runners.run.lgr.warning',
+        lambda s: warnings.append(s)
+    )
+    with pytest.raises(ValueError):
+        with run([
+                sys.executable, '-u', '-c',
+                'import time\n'
+                'time.sleep(5)\n'
+            ],
+            StdOutCaptureGeneratorProtocol,
+        ):
+            raise ValueError('Something')
+    assert warnings[0].startswith('Possible stall:')