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