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import abc
import time
import asyncio
import logging
import warnings
from typing import Optional, Set, Callable, Awaitable
from ..utils import DeadlineWrapper
from ..metadata import Deadline
log = logging.getLogger(__name__)
DEFAULT_CHECK_TTL = 30
DEFAULT_CHECK_TIMEOUT = 10
_Status = Optional[bool]
class CheckBase(abc.ABC):
@abc.abstractmethod
def __status__(self) -> _Status:
pass
@abc.abstractmethod
async def __check__(self) -> _Status:
pass
@abc.abstractmethod
async def __subscribe__(self) -> asyncio.Event:
pass
@abc.abstractmethod
async def __unsubscribe__(self, event: asyncio.Event) -> None:
pass
class ServiceCheck(CheckBase):
"""Performs periodic checks
Example:
.. code-block:: python3
async def db_test():
# raised exceptions are the same as returning False,
# except that exceptions will be logged
await db.execute('SELECT 1;')
return True
db_check = ServiceCheck(db_test)
"""
_value = None
_poll_task = None
_last_check = None
def __init__(
self,
func: Callable[[], Awaitable[_Status]],
*,
loop: Optional[asyncio.AbstractEventLoop] = None,
check_ttl: float = DEFAULT_CHECK_TTL,
check_timeout: float = DEFAULT_CHECK_TIMEOUT,
) -> None:
"""
:param func: callable object which returns awaitable object, where
result is one of: ``True`` (healthy), ``False`` (unhealthy), or
``None`` (unknown)
:param loop: (deprecated) asyncio-compatible event loop
:param check_ttl: how long we can cache result of the previous check
:param check_timeout: timeout for this check
"""
self._func = func
self._check_ttl = check_ttl
self._check_timeout = check_timeout
self._events: Set[asyncio.Event] = set()
if loop:
warnings.warn("The loop argument is deprecated and scheduled "
"for removal in grpclib 0.5",
DeprecationWarning, stacklevel=2)
self._check_lock = asyncio.Event()
self._check_lock.set()
self._check_wrapper = DeadlineWrapper()
def __status__(self) -> _Status:
return self._value
async def __check__(self) -> _Status:
if (
self._last_check is not None
and time.monotonic() - self._last_check < self._check_ttl
):
return self._value
if not self._check_lock.is_set():
# wait until concurrent check succeed
await self._check_lock.wait()
return self._value
prev_value = self._value
self._check_lock.clear()
try:
deadline = Deadline.from_timeout(self._check_timeout)
with self._check_wrapper.start(deadline):
value = await self._func()
if value is not None and not isinstance(value, bool):
raise TypeError('Invalid status type: {!r}'.format(value))
self._value = value
except asyncio.CancelledError:
raise
except Exception:
log.exception('Health check failed')
self._value = False
finally:
self._check_lock.set()
self._last_check = time.monotonic()
if self._value != prev_value:
log_level = log.info if self._value else log.warning
log_level('Health check %r status changed to %r',
self._func, self._value)
# notify all watchers that this check was changed
for event in self._events:
event.set()
return self._value
async def _poll(self) -> None:
while True:
status = await self.__check__()
if status:
await asyncio.sleep(self._check_ttl)
else:
await asyncio.sleep(self._check_ttl) # TODO: change interval?
async def __subscribe__(self) -> asyncio.Event:
if self._poll_task is None:
loop = asyncio.get_event_loop()
self._poll_task = loop.create_task(self._poll())
event = asyncio.Event()
self._events.add(event)
return event
async def __unsubscribe__(self, event: asyncio.Event) -> None:
self._events.discard(event)
if not self._events:
assert self._poll_task is not None
task = self._poll_task
self._poll_task = None
task.cancel()
try:
await task
except asyncio.CancelledError:
pass
class ServiceStatus(CheckBase):
"""Contains status of a proactive check
Example:
.. code-block:: python3
redis_status = ServiceStatus()
# detected that Redis is available
redis_status.set(True)
# detected that Redis is unavailable
redis_status.set(False)
"""
def __init__(
self,
*,
loop: Optional[asyncio.AbstractEventLoop] = None,
) -> None:
"""
:param loop: (deprecated) asyncio-compatible event loop
"""
if loop:
warnings.warn("The loop argument is deprecated and scheduled "
"for removal in grpclib 0.5",
DeprecationWarning, stacklevel=2)
self._value: _Status = None
self._events: Set[asyncio.Event] = set()
def set(self, value: _Status) -> None:
"""Sets current status of a check
:param value: ``True`` (healthy), ``False`` (unhealthy), or ``None``
(unknown)
"""
prev_value = self._value
self._value = value
if self._value != prev_value:
# notify all watchers that this check was changed
for event in self._events:
event.set()
def __status__(self) -> _Status:
return self._value
async def __check__(self) -> _Status:
return self._value
async def __subscribe__(self) -> asyncio.Event:
event = asyncio.Event()
self._events.add(event)
return event
async def __unsubscribe__(self, event: asyncio.Event) -> None:
self._events.discard(event)
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