1# Copyright 2021 The Pigweed Authors 2# 3# Licensed under the Apache License, Version 2.0 (the "License"); you may not 4# use this file except in compliance with the License. You may obtain a copy of 5# the License at 6# 7# https://www.apache.org/licenses/LICENSE-2.0 8# 9# Unless required by applicable law or agreed to in writing, software 10# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT 11# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the 12# License for the specific language governing permissions and limitations under 13# the License. 14"""Simple watchdog class.""" 15 16import threading 17from typing import Any, Callable 18 19 20class Watchdog: 21 """Simple class that times out unless reset. 22 23 This class could be used, for example, to track a device's connection state 24 for devices that send a periodic heartbeat packet. 25 """ 26 def __init__(self, 27 on_reset: Callable[[], Any], 28 on_expiration: Callable[[], Any], 29 while_expired: Callable[[], Any] = lambda: None, 30 timeout_s: float = 1, 31 expired_timeout_s: float = None): 32 """Creates a watchdog; start() must be called to start it. 33 34 Args: 35 on_reset: Function called when the watchdog is reset after having 36 expired. 37 on_expiration: Function called when the timeout expires. 38 while_expired: Function called repeatedly while the watchdog is 39 expired. 40 timeout_s: If reset() is not called for timeout_s, the watchdog 41 expires and calls the on_expiration callback. 42 expired_timeout_s: While expired, the watchdog calls the 43 while_expired callback every expired_timeout_s. 44 """ 45 self._on_reset = on_reset 46 self._on_expiration = on_expiration 47 self._while_expired = while_expired 48 49 self.timeout_s = timeout_s 50 51 if expired_timeout_s is None: 52 self.expired_timeout_s = self.timeout_s * 10 53 else: 54 self.expired_timeout_s = expired_timeout_s 55 56 self.expired: bool = False 57 self._watchdog = threading.Timer(0, self._timeout_expired) 58 59 def start(self) -> None: 60 """Starts the watchdog; must be called for the watchdog to work.""" 61 self._watchdog.cancel() 62 self._watchdog = threading.Timer( 63 self.expired_timeout_s if self.expired else self.timeout_s, 64 self._timeout_expired) 65 self._watchdog.daemon = True 66 self._watchdog.start() 67 68 def reset(self) -> None: 69 """Resets the timeout; calls the on_reset callback if expired.""" 70 if self.expired: 71 self.expired = False 72 self._on_reset() 73 74 self.start() 75 76 def _timeout_expired(self) -> None: 77 if self.expired: 78 self._while_expired() 79 else: 80 self.expired = True 81 self._on_expiration() 82 83 self.start() 84