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timer.py
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timer.py
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"""A timer receiver that returns the timestamp every `interval`.
Copyright
Copyright © 2022 Frequenz Energy-as-a-Service GmbH
License
MIT
"""
import asyncio
from datetime import datetime, timedelta
from typing import Optional
from frequenz.channels.base_classes import Receiver
class Timer(Receiver[datetime]):
"""A timer receiver that returns the timestamp every `interval` seconds.
Primarily for use with `channel.Select` calls.
When you want something to happen with a fixed period:
```
timer = channel.Timer(30.0)
select = Select(bat_1 = receiver1, timer = timer)
while await select.ready():
if msg := select.bat_1:
if val := msg.inner:
process_data(val)
else:
logging.warn("battery channel closed")
elif ts := select.timer:
# something to do once every 30 seconds
pass
```
When you want something to happen when nothing else has happened in a
certain interval:
```
timer = channel.Timer(30.0)
select = Select(bat_1 = receiver1, timer = timer)
while await select.ready():
timer.reset()
if msg := select.bat_1:
if val := msg.inner:
process_data(val)
else:
logging.warn("battery channel closed")
elif ts := select.timer:
# something to do if there's no battery data for 30 seconds
pass
```
"""
def __init__(self, interval: float) -> None:
"""Create a `LocalTimer` instance.
Args:
interval: number of seconds between messages.
"""
self._stopped = False
self._interval = timedelta(seconds=interval)
self._next_msg_time = datetime.now() + self._interval
def reset(self) -> None:
"""Reset the timer to start timing from `now`."""
self._next_msg_time = datetime.now() + self._interval
def stop(self) -> None:
"""Stop the timer.
Once `stop` has been called, all subsequent calls to `receive` will
immediately return None.
"""
self._stopped = True
async def receive(self) -> Optional[datetime]:
"""Return the current time once the next tick is due.
Returns:
The time of the next tick.
"""
if self._stopped:
return None
now = datetime.now()
diff = self._next_msg_time - now
while diff.total_seconds() > 0:
await asyncio.sleep(diff.total_seconds())
now = datetime.now()
diff = self._next_msg_time - now
self._next_msg_time = now + self._interval
return now