3 """Several helpers to keep track of internal state via periodic
4 polling. StateTracker expects to be invoked periodically to maintain
5 state whereas the others automatically update themselves and,
6 optionally, expose an event for client code to wait on state changes."""
12 from abc import ABC, abstractmethod
13 from typing import Dict, Optional
17 from thread_utils import background_thread
19 logger = logging.getLogger(__name__)
22 class StateTracker(ABC):
23 """A base class that maintains and updates a global state via an
24 update routine. Instances of this class should be periodically
25 invoked via the heartbeat() method. This method, in turn, invokes
26 update() with update_ids according to a schedule / periodicity
27 provided to the c'tor.
31 def __init__(self, update_ids_to_update_secs: Dict[str, float]) -> None:
32 """The update_ids_to_update_secs dict parameter describes one or more
33 update types (unique update_ids) and the periodicity(ies), in
34 seconds, at which it/they should be invoked.
36 Note that, when more than one update is overdue, they will be
37 invoked in order by their update_ids so care in choosing these
38 identifiers may be in order.
41 self.update_ids_to_update_secs = update_ids_to_update_secs
42 self.last_reminder_ts: Dict[str, Optional[datetime.datetime]] = {}
43 self.now: Optional[datetime.datetime] = None
44 for x in update_ids_to_update_secs.keys():
45 self.last_reminder_ts[x] = None
51 now: datetime.datetime,
52 last_invocation: Optional[datetime.datetime],
54 """Put whatever you want here. The update_id will be the string
55 passed to the c'tor as a key in the Dict. It will only be
56 tapped on the shoulder, at most, every update_secs seconds.
57 The now param is the approximate current timestamp and the
58 last_invocation param is the last time you were invoked (or
59 None on the first invocation)
64 def heartbeat(self, *, force_all_updates_to_run: bool = False) -> None:
65 """Invoke this method to cause the StateTracker instance to identify
66 and invoke any overdue updates based on the schedule passed to
67 the c'tor. In the base StateTracker class, this method must
68 be invoked manually with a thread from external code.
70 If more than one type of update (update_id) are overdue,
71 they will be invoked in order based on their update_ids.
73 Setting force_all_updates_to_run will invoke all updates
74 (ordered by update_id) immediately ignoring whether or not
78 self.now = datetime.datetime.now(tz=pytz.timezone("US/Pacific"))
79 for update_id in sorted(self.last_reminder_ts.keys()):
80 if force_all_updates_to_run:
81 logger.debug('Forcing all updates to run')
82 self.update(update_id, self.now, self.last_reminder_ts[update_id])
83 self.last_reminder_ts[update_id] = self.now
86 refresh_secs = self.update_ids_to_update_secs[update_id]
87 last_run = self.last_reminder_ts[update_id]
88 if last_run is None: # Never run before
89 logger.debug('id %s has never been run; running it now', update_id)
90 self.update(update_id, self.now, self.last_reminder_ts[update_id])
91 self.last_reminder_ts[update_id] = self.now
93 delta = self.now - last_run
94 if delta.total_seconds() >= refresh_secs: # Is overdue?
95 logger.debug('id %s is overdue; running it now', update_id)
99 self.last_reminder_ts[update_id],
101 self.last_reminder_ts[update_id] = self.now
104 class AutomaticStateTracker(StateTracker):
105 """Just like HeartbeatCurrentState but you don't need to pump the
106 heartbeat; it runs on a background thread. Call .shutdown() to
107 terminate the updates.
112 def pace_maker(self, should_terminate: threading.Event) -> None:
113 """Entry point for a background thread to own calling heartbeat()
114 at regular intervals so that the main thread doesn't need to do
119 if should_terminate.is_set():
120 logger.debug('pace_maker noticed event; shutting down')
123 logger.debug('pace_maker is sleeping for %.1fs', self.sleep_delay)
124 time.sleep(self.sleep_delay)
128 update_ids_to_update_secs: Dict[str, float],
130 override_sleep_delay: Optional[float] = None,
134 super().__init__(update_ids_to_update_secs)
135 if override_sleep_delay is not None:
136 logger.debug('Overriding sleep delay to %.1f', override_sleep_delay)
137 self.sleep_delay = override_sleep_delay
139 periods_list = list(update_ids_to_update_secs.values())
140 self.sleep_delay = math_utils.gcd_float_sequence(periods_list)
141 logger.info('Computed sleep_delay=%.1f', self.sleep_delay)
142 (thread, stop_event) = self.pace_maker()
143 self.should_terminate = stop_event
144 self.updater_thread = thread
147 """Terminates the background thread and waits for it to tear down.
148 This may block for as long as self.sleep_delay.
151 logger.debug('Setting shutdown event and waiting for background thread.')
152 self.should_terminate.set()
153 self.updater_thread.join()
154 logger.debug('Background thread terminated.')
157 class WaitableAutomaticStateTracker(AutomaticStateTracker):
158 """This is an AutomaticStateTracker that exposes a wait method which
159 will block the calling thread until the state changes with an
160 optional timeout. The caller should check the return value of
161 wait; it will be true if something changed and false if the wait
162 simply timed out. If the return value is true, the instance
163 should be reset() before wait is called again.
167 detector = waitable_presence.WaitableAutomaticStateSubclass()
169 changed = detector.wait(timeout=60 * 5)
172 # Figure out what changed and react
174 # Just a timeout; no need to reset. Maybe do something
175 # else before looping up into wait again.
181 update_ids_to_update_secs: Dict[str, float],
183 override_sleep_delay: Optional[float] = None,
185 self._something_changed = threading.Event()
186 super().__init__(update_ids_to_update_secs, override_sleep_delay=override_sleep_delay)
188 def something_changed(self):
189 self._something_changed.set()
191 def did_something_change(self) -> bool:
192 return self._something_changed.is_set()
195 self._something_changed.clear()
197 def wait(self, *, timeout=None):
198 return self._something_changed.wait(timeout=timeout)