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# SPDX-License-Identifier: AGPL-3.0-or-later
# lint: pylint
# pylint: disable=missing-module-docstring
"""Lame scheduler which use Redis as a source of truth:
* the Redis key SearXNG_checker_next_call_ts contains the next time the embedded checker should run.
* to avoid lock, a unique Redis script reads and updates the Redis key SearXNG_checker_next_call_ts.
* this Redis script returns a list of two elements:
* the first one is a boolean. If True, the embedded checker must run now in this worker.
* the second element is the delay in second to wait before the next call to the Redis script.
This scheduler is not generic on purpose: if more feature are required, a dedicate scheduler must be used
(= a better scheduler should not use the web workers)
"""
import logging
import time
import importlib
from typing import Callable
from searx.redisdb import client as get_redis_client
from searx.redislib import lua_script_storage
logger = logging.getLogger('searx.search.checker')
def scheduler_function(start_after_from: int, start_after_to: int, every_from: int, every_to: int, callback: Callable):
"""Run the checker periodically. The function never returns.
Parameters:
* start_after_from and start_after_to: when to call "callback" for the first on the Redis instance
* every_from and every_to: after the first call, how often to call "callback"
There is no issue:
* to call this function is multiple workers
* to kill workers at any time as long there is one at least one worker
"""
scheduler_now_script = importlib.resources.read_text(__package__, "scheduler.lua")
while True:
# ask the Redis script what to do
# the script says
# * if the checker must run now.
# * how to long to way before calling the script again (it can be call earlier, but not later).
script = lua_script_storage(get_redis_client(), scheduler_now_script)
call_now, wait_time = script(args=[start_after_from, start_after_to, every_from, every_to])
# does the worker run the checker now?
if call_now:
# run the checker
try:
callback()
except Exception: # pylint: disable=broad-except
logger.exception("Error calling the embedded checker")
# only worker display the wait_time
logger.info("Next call to the checker in %s seconds", wait_time)
# wait until the next call
time.sleep(wait_time)
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