call pthred_sigmask to restore CTRL-C handling

conda_libmamba_solver/mamba_utils.py

@@ -9,13 +9,15 @@
 # 2022.11.14: only keeping channel prioritization and context initialization logic now
 
 import logging
+import signal
 from functools import lru_cache
 from importlib.metadata import version
 from typing import Dict
 
 import libmambapy as api
 from conda.base.constants import ChannelPriority
 from conda.base.context import context
+from conda.common.compat import on_win
 
 log = logging.getLogger(f"conda.{__name__}")
 
@@ -84,8 +86,28 @@ def set_channel_priorities(index: Dict[str, "_ChannelRepoInfo"], has_priority: b
     return index
 
 
+_once = False
+
+
 def init_api_context() -> api.Context:
+    global _once
+
     api_ctx = api.Context()
+    # Override mamba's signal handling which would otherwise disable CTRL-C etc.
+    # in Python. The signal handling doesn't appear to be used in solver, but is
+    # definitely used to make other parts of libmamba interruptible. Those parts
+    # of libmamba might also set and reset the signal handler. An alternative
+    # and possible better solution would be to override libmamba's signal
+    # handler to also call
+    # https://docs.python.org/3/c-api/exceptions.html#c.PyErr_SetInterruptEx or
+    # to have an overridable callback for that system, that would then call
+    # PyErr_SetInterruptEx.
+    if not _once:
+        _once = True
+        if not on_win:
+            signal.pthread_sigmask(signal.SIG_UNBLOCK, signal.valid_signals())
+        else:
+            signal.signal(signal.SIGINT, signal.SIG_DFL)
 
     # Output params
     # We use this getattr() trick to guarantee backwards compatibility

news/339-pthread-sigmask

@@ -0,0 +1,19 @@
+### Enhancements
+
+* <news item>
+
+### Bug fixes
+
+* Call `pthread_sigmask()` to override Mamba's signal handling, allowing `CTRL-C` to raise `KeyboardInterrupt` in Python. (#339)
+
+### Deprecations
+
+* <news item>
+
+### Docs
+
+* <news item>
+
+### Other
+
+* <news item>

tests/test_workarounds.py

@@ -2,8 +2,12 @@
 # Copyright (C) 2023 conda
 # SPDX-License-Identifier: BSD-3-Clause
 import json
+import signal
 import sys
-from subprocess import PIPE, check_call, run
+import time
+from subprocess import PIPE, Popen, check_call, run
+
+import pytest
 
 
 def test_matchspec_star_version():
@@ -56,3 +60,35 @@ def test_build_string_filters():
             assert pkg["version"].startswith("3.8")
         if pkg["name"] == "numpy":
             assert "py38" in pkg["build_string"]
+
+
+@pytest.mark.parametrize("stage", ["Collecting package metadata", "Solving environment"])
+def test_ctrl_c(stage):
+    p = Popen(
+        [
+            sys.executable,
+            "-m",
+            "conda",
+            "create",
+            "-p",
+            "UNUSED",
+            "--dry-run",
+            "--solver=libmamba",
+            "--override-channels",
+            "--channel=conda-forge",
+            "vaex",
+        ],
+        text=True,
+        stdout=PIPE,
+        stderr=PIPE,
+    )
+    t0 = time.time()
+    while stage not in p.stdout.readline():
+        time.sleep(0.1)
+        if time.time() - t0 > 30:
+            raise RuntimeError("Timeout")
+
+    p.send_signal(signal.SIGINT if sys.platform != "win32" else signal.CTRL_C_EVENT)
+    p.wait()
+    assert p.returncode != 0
+    assert "KeyboardInterrupt" in p.stdout.read() + p.stderr.read()