pip/tests/lib/compat.py

# mypy: no-warn-unused-ignores

import contextlib
import signal
from typing import Callable, ContextManager, Iterable, Iterator

# Applies on Windows.
if not hasattr(signal, "pthread_sigmask"):
    # We're not relying on this behavior anywhere currently, it's just best
    # practice.
    blocked_signals: Callable[[], ContextManager[None]] = contextlib.nullcontext
else:

    @contextlib.contextmanager
    def blocked_signals() -> Iterator[None]:
        """Block all signals for e.g. starting a worker thread."""
        # valid_signals() was added in Python 3.8 (and not using it results
        # in a warning on pthread_sigmask() call)
        mask: Iterable[int]
        try:
            mask = signal.valid_signals()
        except AttributeError:
            mask = set(range(1, signal.NSIG))

        old_mask = signal.pthread_sigmask(  # type: ignore[attr-defined]
            signal.SIG_SETMASK,  # type: ignore[attr-defined]
            mask,
        )
        try:
            yield
        finally:
            signal.pthread_sigmask(  # type: ignore[attr-defined]
                signal.SIG_SETMASK,  # type: ignore[attr-defined]
                old_mask,
            )