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Support reactor timing metric on more reactors. (#16532)
Previously only Twisted's EPollReactor was compatible with the reactor timing metric, notably not working when asyncio was used. After this change, the following configurations support the reactor timing metric: * poll, epoll, or select reactors * asyncio reactor with a poll, epoll, select, /dev/poll, or kqueue event loop.
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3 changed files with 105 additions and 28 deletions
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changelog.d/16532.misc
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changelog.d/16532.misc
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@ -0,0 +1 @@
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Support reactor tick timings on more types of event loops.
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mypy.ini
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mypy.ini
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@ -37,8 +37,8 @@ files =
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build_rust.py
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[mypy-synapse.metrics._reactor_metrics]
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# This module imports select.epoll. That exists on Linux, but doesn't on macOS.
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# See https://github.com/matrix-org/synapse/pull/11771.
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# This module pokes at the internals of OS-specific classes, to appease mypy
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# on different systems we add additional ignores.
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warn_unused_ignores = False
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[mypy-synapse.util.caches.treecache]
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@ -12,17 +12,45 @@
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import select
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import logging
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import time
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from typing import Any, Iterable, List, Tuple
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from selectors import SelectSelector, _PollLikeSelector # type: ignore[attr-defined]
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from typing import Any, Callable, Iterable
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from prometheus_client import Histogram, Metric
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from prometheus_client.core import REGISTRY, GaugeMetricFamily
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from twisted.internet import reactor
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from twisted.internet import reactor, selectreactor
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from twisted.internet.asyncioreactor import AsyncioSelectorReactor
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from synapse.metrics._types import Collector
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try:
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from selectors import KqueueSelector
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except ImportError:
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class KqueueSelector: # type: ignore[no-redef]
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pass
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try:
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from twisted.internet.epollreactor import EPollReactor
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except ImportError:
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class EPollReactor: # type: ignore[no-redef]
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pass
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try:
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from twisted.internet.pollreactor import PollReactor
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except ImportError:
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class PollReactor: # type: ignore[no-redef]
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pass
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logger = logging.getLogger(__name__)
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#
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# Twisted reactor metrics
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#
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@ -34,52 +62,100 @@ tick_time = Histogram(
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)
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class EpollWrapper:
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"""a wrapper for an epoll object which records the time between polls"""
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class CallWrapper:
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"""A wrapper for a callable which records the time between calls"""
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def __init__(self, poller: "select.epoll"): # type: ignore[name-defined]
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def __init__(self, wrapped: Callable[..., Any]):
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self.last_polled = time.time()
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self._poller = poller
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self._wrapped = wrapped
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def poll(self, *args, **kwargs) -> List[Tuple[int, int]]: # type: ignore[no-untyped-def]
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# record the time since poll() was last called. This gives a good proxy for
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def __call__(self, *args, **kwargs) -> Any: # type: ignore[no-untyped-def]
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# record the time since this was last called. This gives a good proxy for
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# how long it takes to run everything in the reactor - ie, how long anything
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# waiting for the next tick will have to wait.
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tick_time.observe(time.time() - self.last_polled)
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ret = self._poller.poll(*args, **kwargs)
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ret = self._wrapped(*args, **kwargs)
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self.last_polled = time.time()
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return ret
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class ObjWrapper:
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"""A wrapper for an object which wraps a specified method in CallWrapper.
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Other methods/attributes are passed to the original object.
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This is necessary when the wrapped object does not allow the attribute to be
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overwritten.
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"""
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def __init__(self, wrapped: Any, method_name: str):
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self._wrapped = wrapped
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self._method_name = method_name
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self._wrapped_method = CallWrapper(getattr(wrapped, method_name))
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def __getattr__(self, item: str) -> Any:
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return getattr(self._poller, item)
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if item == self._method_name:
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return self._wrapped_method
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return getattr(self._wrapped, item)
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class ReactorLastSeenMetric(Collector):
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def __init__(self, epoll_wrapper: EpollWrapper):
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self._epoll_wrapper = epoll_wrapper
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def __init__(self, call_wrapper: CallWrapper):
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self._call_wrapper = call_wrapper
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def collect(self) -> Iterable[Metric]:
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cm = GaugeMetricFamily(
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"python_twisted_reactor_last_seen",
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"Seconds since the Twisted reactor was last seen",
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)
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cm.add_metric([], time.time() - self._epoll_wrapper.last_polled)
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cm.add_metric([], time.time() - self._call_wrapper.last_polled)
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yield cm
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# Twisted has already select a reasonable reactor for us, so assumptions can be
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# made about the shape.
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wrapper = None
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try:
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# if the reactor has a `_poller` attribute, which is an `epoll` object
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# (ie, it's an EPollReactor), we wrap the `epoll` with a thing that will
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# measure the time between ticks
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from select import epoll # type: ignore[attr-defined]
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if isinstance(reactor, (PollReactor, EPollReactor)):
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reactor._poller = ObjWrapper(reactor._poller, "poll") # type: ignore[attr-defined]
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wrapper = reactor._poller._wrapped_method # type: ignore[attr-defined]
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poller = reactor._poller # type: ignore[attr-defined]
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except (AttributeError, ImportError):
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pass
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else:
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if isinstance(poller, epoll):
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poller = EpollWrapper(poller)
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reactor._poller = poller # type: ignore[attr-defined]
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REGISTRY.register(ReactorLastSeenMetric(poller))
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elif isinstance(reactor, selectreactor.SelectReactor):
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# Twisted uses a module-level _select function.
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wrapper = selectreactor._select = CallWrapper(selectreactor._select)
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elif isinstance(reactor, AsyncioSelectorReactor):
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# For asyncio look at the underlying asyncio event loop.
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asyncio_loop = reactor._asyncioEventloop # A sub-class of BaseEventLoop,
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# A sub-class of BaseSelector.
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selector = asyncio_loop._selector # type: ignore[attr-defined]
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if isinstance(selector, SelectSelector):
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wrapper = selector._select = CallWrapper(selector._select) # type: ignore[attr-defined]
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# poll, epoll, and /dev/poll.
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elif isinstance(selector, _PollLikeSelector):
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selector._selector = ObjWrapper(selector._selector, "poll") # type: ignore[attr-defined]
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wrapper = selector._selector._wrapped_method # type: ignore[attr-defined]
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elif isinstance(selector, KqueueSelector):
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selector._selector = ObjWrapper(selector._selector, "control") # type: ignore[attr-defined]
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wrapper = selector._selector._wrapped_method # type: ignore[attr-defined]
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else:
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# E.g. this does not support the (Windows-only) ProactorEventLoop.
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logger.warning(
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"Skipping configuring ReactorLastSeenMetric: unexpected asyncio loop selector: %r via %r",
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selector,
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asyncio_loop,
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)
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except Exception as e:
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logger.warning("Configuring ReactorLastSeenMetric failed: %r", e)
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if wrapper:
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REGISTRY.register(ReactorLastSeenMetric(wrapper))
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