Class _VirtualTimeLoop

tests/virtual_time.py:290–316

A `SelectorEventLoop` whose clock only advances when the loop would otherwise sleep. The selector jumps the virtual clock straight to the next scheduled callback (see :class:`_AutojumpSelector`), so timing-coupled tests run in ~0 wall time and deterministically. Same-instant timers are

class _VirtualTimeLoop(asyncio.SelectorEventLoop):
    """A `SelectorEventLoop` whose clock only advances when the loop would otherwise sleep.

    The selector jumps the virtual clock straight to the next scheduled callback (see
    :class:`_AutojumpSelector`), so timing-coupled tests run in ~0 wall time and deterministically.
    Same-instant timers are nudged into scheduling (FIFO) order so they fire in the causal order
    real wall time would produce.
    """

    def __init__(self) -> None:
        self._virtual_clock = _VirtualClock()
        super().__init__(selector=_AutojumpSelector(self._virtual_clock))
        # Resolve finely enough that the sub-nanosecond tie-break is representable and only the
        # exact-same-instant timer fires per jump.
        self._clock_resolution = _FINE_RESOLUTION
        self._tie_seq = 0

    def time(self) -> float:
        return self._virtual_clock.time()

    def monotonic_read(self) -> float:
        """Strictly-increasing wall-clock read off this loop's clock (see _VirtualClock.read)."""
        return self._virtual_clock.read()

    def call_at(self, when: float, callback: Any, *args: Any, **kwargs: Any) -> Any:
        self._tie_seq += 1
        return super().call_at(when + self._tie_seq * _TIE_BREAK, callback, *args, **kwargs)


class _VirtualTimePolicy(asyncio.DefaultEventLoopPolicy):