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.
This commit is contained in:
Patrick Cloke 2023-11-06 08:31:22 -05:00 committed by GitHub
parent 1a9b22a3d1
commit cc4fe68adf
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3 changed files with 105 additions and 28 deletions

1
changelog.d/16532.misc Normal file
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@ -0,0 +1 @@
Support reactor tick timings on more types of event loops.

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@ -37,8 +37,8 @@ files =
build_rust.py
[mypy-synapse.metrics._reactor_metrics]
# This module imports select.epoll. That exists on Linux, but doesn't on macOS.
# See https://github.com/matrix-org/synapse/pull/11771.
# This module pokes at the internals of OS-specific classes, to appease mypy
# on different systems we add additional ignores.
warn_unused_ignores = False
[mypy-synapse.util.caches.treecache]

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@ -12,17 +12,45 @@
# See the License for the specific language governing permissions and
# limitations under the License.
import select
import logging
import time
from typing import Any, Iterable, List, Tuple
from selectors import SelectSelector, _PollLikeSelector # type: ignore[attr-defined]
from typing import Any, Callable, Iterable
from prometheus_client import Histogram, Metric
from prometheus_client.core import REGISTRY, GaugeMetricFamily
from twisted.internet import reactor
from twisted.internet import reactor, selectreactor
from twisted.internet.asyncioreactor import AsyncioSelectorReactor
from synapse.metrics._types import Collector
try:
from selectors import KqueueSelector
except ImportError:
class KqueueSelector: # type: ignore[no-redef]
pass
try:
from twisted.internet.epollreactor import EPollReactor
except ImportError:
class EPollReactor: # type: ignore[no-redef]
pass
try:
from twisted.internet.pollreactor import PollReactor
except ImportError:
class PollReactor: # type: ignore[no-redef]
pass
logger = logging.getLogger(__name__)
#
# Twisted reactor metrics
#
@ -34,52 +62,100 @@ tick_time = Histogram(
)
class EpollWrapper:
"""a wrapper for an epoll object which records the time between polls"""
class CallWrapper:
"""A wrapper for a callable which records the time between calls"""
def __init__(self, poller: "select.epoll"): # type: ignore[name-defined]
def __init__(self, wrapped: Callable[..., Any]):
self.last_polled = time.time()
self._poller = poller
self._wrapped = wrapped
def poll(self, *args, **kwargs) -> List[Tuple[int, int]]: # type: ignore[no-untyped-def]
# record the time since poll() was last called. This gives a good proxy for
def __call__(self, *args, **kwargs) -> Any: # type: ignore[no-untyped-def]
# record the time since this was last called. This gives a good proxy for
# how long it takes to run everything in the reactor - ie, how long anything
# waiting for the next tick will have to wait.
tick_time.observe(time.time() - self.last_polled)
ret = self._poller.poll(*args, **kwargs)
ret = self._wrapped(*args, **kwargs)
self.last_polled = time.time()
return ret
class ObjWrapper:
"""A wrapper for an object which wraps a specified method in CallWrapper.
Other methods/attributes are passed to the original object.
This is necessary when the wrapped object does not allow the attribute to be
overwritten.
"""
def __init__(self, wrapped: Any, method_name: str):
self._wrapped = wrapped
self._method_name = method_name
self._wrapped_method = CallWrapper(getattr(wrapped, method_name))
def __getattr__(self, item: str) -> Any:
return getattr(self._poller, item)
if item == self._method_name:
return self._wrapped_method
return getattr(self._wrapped, item)
class ReactorLastSeenMetric(Collector):
def __init__(self, epoll_wrapper: EpollWrapper):
self._epoll_wrapper = epoll_wrapper
def __init__(self, call_wrapper: CallWrapper):
self._call_wrapper = call_wrapper
def collect(self) -> Iterable[Metric]:
cm = GaugeMetricFamily(
"python_twisted_reactor_last_seen",
"Seconds since the Twisted reactor was last seen",
)
cm.add_metric([], time.time() - self._epoll_wrapper.last_polled)
cm.add_metric([], time.time() - self._call_wrapper.last_polled)
yield cm
# Twisted has already select a reasonable reactor for us, so assumptions can be
# made about the shape.
wrapper = None
try:
# if the reactor has a `_poller` attribute, which is an `epoll` object
# (ie, it's an EPollReactor), we wrap the `epoll` with a thing that will
# measure the time between ticks
from select import epoll # type: ignore[attr-defined]
if isinstance(reactor, (PollReactor, EPollReactor)):
reactor._poller = ObjWrapper(reactor._poller, "poll") # type: ignore[attr-defined]
wrapper = reactor._poller._wrapped_method # type: ignore[attr-defined]
poller = reactor._poller # type: ignore[attr-defined]
except (AttributeError, ImportError):
pass
else:
if isinstance(poller, epoll):
poller = EpollWrapper(poller)
reactor._poller = poller # type: ignore[attr-defined]
REGISTRY.register(ReactorLastSeenMetric(poller))
elif isinstance(reactor, selectreactor.SelectReactor):
# Twisted uses a module-level _select function.
wrapper = selectreactor._select = CallWrapper(selectreactor._select)
elif isinstance(reactor, AsyncioSelectorReactor):
# For asyncio look at the underlying asyncio event loop.
asyncio_loop = reactor._asyncioEventloop # A sub-class of BaseEventLoop,
# A sub-class of BaseSelector.
selector = asyncio_loop._selector # type: ignore[attr-defined]
if isinstance(selector, SelectSelector):
wrapper = selector._select = CallWrapper(selector._select) # type: ignore[attr-defined]
# poll, epoll, and /dev/poll.
elif isinstance(selector, _PollLikeSelector):
selector._selector = ObjWrapper(selector._selector, "poll") # type: ignore[attr-defined]
wrapper = selector._selector._wrapped_method # type: ignore[attr-defined]
elif isinstance(selector, KqueueSelector):
selector._selector = ObjWrapper(selector._selector, "control") # type: ignore[attr-defined]
wrapper = selector._selector._wrapped_method # type: ignore[attr-defined]
else:
# E.g. this does not support the (Windows-only) ProactorEventLoop.
logger.warning(
"Skipping configuring ReactorLastSeenMetric: unexpected asyncio loop selector: %r via %r",
selector,
asyncio_loop,
)
except Exception as e:
logger.warning("Configuring ReactorLastSeenMetric failed: %r", e)
if wrapper:
REGISTRY.register(ReactorLastSeenMetric(wrapper))