fix: change start_time source in CronTrigger.next_fire()

[mifuyutsuki]

Pull Request Type

• Feature addition
• Bugfix
• Documentation update
• Code refactor
• Tests improvement
• CI/CD pipeline enhancement
• Other: [Replace with a description]

Description

Changes the source of start_time in CronTrigger.next_fire() to fix a bug causing possible multiple firing.

This fix ensures that the next firing time of the task trigger would always advance after the task is fired. Before the fix, it is possible for the next fire to not advance, due to using datetime.now() for the reference start time and the possibility that the task fires just moments before the supposed start time. See attached issue for illustration.

Changes

• Change start time of croniter in CronTrigger.next_fire() from datetime.now() to self.last_call_time.

Related Issues

#1717

Test Scenarios

The following creates a cron-triggered task every minute to print the current time to standard output.

from interactions import Client, Intents, Task, listen, CronTrigger
from datetime import datetime
bot = Client(intents=Intents.DEFAULT)

@listen()
async def on_startup():
  test_task.start()

@Task.create(CronTrigger("* * * * *"))
async def test_task():
  print(datetime.now().isoformat())

bot.start("token")

Example output before fix:

2024-07-17T01:24:00.017566
2024-07-17T01:25:00.001133
2024-07-17T01:27:00.009860
2024-07-17T01:27:59.998935
2024-07-17T01:27:59.999933
2024-07-17T01:28:00.000932
2024-07-17T01:29:00.019318
2024-07-17T01:30:00.005986
2024-07-17T01:30:59.999633
2024-07-17T01:31:00.000635
2024-07-17T01:32:00.005908

Example output after fix:

2024-07-17T01:34:00.000212
2024-07-17T01:35:00.010656
2024-07-17T01:36:00.006000
2024-07-17T01:36:59.993675
2024-07-17T01:38:00.008853
2024-07-17T01:39:00.020538
2024-07-17T01:40:00.002984
2024-07-17T01:41:00.017267
2024-07-17T01:42:00.019774
2024-07-17T01:42:59.995745
2024-07-17T01:43:59.997304

Python Compatibility

• I've ensured my code works on Python 3.10.x
• I've ensured my code works on Python 3.11.x

Checklist

• I've run the pre-commit code linter over all edited files
• I've tested my changes on supported Python versions
• I've added tests for my code, if applicable
• I've updated / added documentation, where applicable