前言
因为项目原因选择了gearman作为任务委派的中间件,但原生的python拓展包只支持单进程,期间为了将gearman改造成自适应多进程的方式在实现方式上走进了些误区,故在此记录这些误区的坑以及目前的最优解决方案。
实现思路
实现方式
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主进程接收任务,子进程处理任务。以一个主进程作为任务委派的接收进程,接收到任务后将任务分派给子进程进行处理,处理完成后由该子进程直接返回任务结果给gearman。
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多进程接收并处理任务。批量fork多个子进程注册任务,子进程间互不影响,各自完成接收、处理任务的过程。
先说说第一种实现方式的优缺点
优点:
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由于worker较多的时间是消耗在等待接收请求上,因此主进程只单一的进行轮训任务接收可以提高单条gearman请求通道的利用率。
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由子进程直接返回任务结果可分离主进程与子进程的作业,主进程无需关心任务的结果而只专注于接收任务。
缺点:
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主进程接收到任务请求后将请求转发给子进程处理任务,由于子进程处理任务完成后需要将任务结果返回给gearman,因此子进程需要将该任务请求对应的gearman socket传递给子进程,而该过程实现起来过于复杂。(通常具有socket的实例无法通过pickle传递给子进程,虽然Unix的sendmsg可以用来传递socket,但将传递的socket构造成一个GearmanWorker又是另外一件痛苦的事情)
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子进程通过传递的socket构造出GearmanWorker后,由于原socket的句柄仍被父进程持有,所以在等待结果的任务请求方无法收到子进程所返回的处理结果。
再来说说第二种实现方式的优缺点
优点:
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等价于fork多个原进程,逻辑、作业方式均无改变。
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可在fork子进程之前完成公有资源的加载而无需每个GearmanWorker匀加载一次。
缺点:
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子进程异常退出后主进程无法正确感知,虽然主进程会维持相同的子进程数,但是异常退出所重启的子进程没有正确注册到gearman接收任务。
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主进程异常退出后子进程无法感知,将导致出现僵尸进程。
选择第二种方案,针对缺点的解决办法
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利用PID文件记录每个子进程的pid,确保主进程退出后仍能通过PID文件退出子进程。
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利用Redis的发布订阅模式实现GearmanWorker的正常退出。
client 端代码: test_multi_gearman_worker.py
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#!/usr/bin/env python
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from gearman import GearmanClient
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gearman_client = GearmanClient(['10.10.13.5:4730'])
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new_jobs = [
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dict(task='test_multi_gearman_worker', data='job-0.mp4'),
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dict(task='test_multi_gearman_worker', data='job-1.mp4'),
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dict(task='test_multi_gearman_worker', data='job-2.mp4'),
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dict(task='test_multi_gearman_worker', data='job-3.mp4'),
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dict(task='test_multi_gearman_worker', data='job-4.mp4'),
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dict(task='test_multi_gearman_worker', data='job-5.mp4'),
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dict(task='test_multi_gearman_worker', data='job-6.mp4'),
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dict(task='test_multi_gearman_worker', data='job-7.mp4'),
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dict(task='test_multi_gearman_worker', data='job-8.mp4'),
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dict(task='test_multi_gearman_worker', data='job-9.mp4'),
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dict(task='test_multi_gearman_worker', data='job-10.mp4'),
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]
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completed_requests = gearman_client.submit_multiple_jobs(new_jobs)
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for current_request in completed_requests:
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print (current_request.result)
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print ("Game over!")
worker端代码: multi-gearman-worker.py
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#!/usr/bin/env python
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import os
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import string
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import signal
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import threading
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import subprocess
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import multiprocessing
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import redis
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from gearman.worker import GearmanWorker, POLL_TIMEOUT_IN_SECONDS
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WORKER_PROCESS_PID = '/tmp/multi_gearman_worker.pid'
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class MultiGearmanWorker(GearmanWorker):
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""" multi-process gearman worker """
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def __init__(self, host_list=None, redis_host=None, redis_port=None, pid=WORKER_PROCESS_PID):
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super(MultiGearmanWorker, self).__init__(host_list=host_list)
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self.redis_host = redis_host
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self.redis_port = redis_port
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self.pid = pid
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def work(self, poll_timeout=POLL_TIMEOUT_IN_SECONDS, process=multiprocessing.cpu_count()):
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"""
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start working, blocking process first
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:param poll_timeout: int , the connection time of gearman
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:param process: int , the number of process for working , the default is the number of cpu-core
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:return:
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"""
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print('Clear last process.')
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self.gearman_worker_exit()
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print('Ready to start %d process for work.' % process)
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gm_poll = multiprocessing.Pool(process)
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for x in range(0, process):
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print('start %d child process', x)
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gm_poll.apply_async(gearman_work, (self, poll_timeout, self.pid))
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gm_poll.close()
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gm_poll.join()
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# Delete the PID file if all sub-process exit normally
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if os.path.isfile(self.pid):
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os.remove(self.pid)
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print('Multi gearman worker exit.')
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def gearman_worker_exit(self):
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""" Terminate sub-process """
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if not os.path.isfile(self.pid):
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return True
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with open(self.pid, 'r+') as f:
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for pid in f.readlines():
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pid = int(pid)
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try:
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os.kill(pid, signal.SIGKILL)
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print('Kill process %d.' % pid)
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except OSError:
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print('Process %d not exists' % pid)
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continue
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os.remove(self.pid)
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print('Remove process pid file.')
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return True
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#The gearman job switch identifier used by the child process
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GEARMAN_CONTINUE_WORK = True
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def gearman_work(gm_worker, poll_timeout=POLL_TIMEOUT_IN_SECONDS, pid=WORKER_PROCESS_PID):
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""" Open gearman;s worker in multiple processes """
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try:
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""" Record the child process pid,
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so that the main process is cleared by the supervisor
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to clear the child process did not exit the last time
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"""
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with open(pid, 'a+') as f:
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f.write("%d%s" % (os.getpid(), os.linesep))
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print('Child process start for work.')
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continue_working = True
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worker_connections = []
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d = threading.Thread(name='monitor', target=gearman_monitor,
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args=(gm_worker.redis_host, gm_worker.redis_port))
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d.start()
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def continue_while_connections_alive(any_activity):
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return gm_worker.after_poll(any_activity)
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# Shuffle our connections after the poll timeout
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while continue_working and GEARMAN_CONTINUE_WORK:
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worker_connections = gm_worker.establish_worker_connections()
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continue_working = gm_worker.poll_connections_until_stopped(
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worker_connections, continue_while_connections_alive, timeout=poll_timeout)
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# If we were kicked out of the worker loop, we should shutdown all our connections
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for current_connection in worker_connections:
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current_connection.close()
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print('Gearman worker closed')
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return None
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except Exception as e:
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print(e)
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def gearman_monitor(redis_host, redis_port):
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""" Listen to dynamic update instructions """
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global GEARMAN_CONTINUE_WORK
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print('Start gearman monitor.')
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while GEARMAN_CONTINUE_WORK:
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"""To prevent abnormal operation caused by the thread is not monitoring the redis response after hanging up,
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exception handling on here, after an exception re-listen
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"""
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try:
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sub = redis.StrictRedis(redis_host, redis_port).pubsub()
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sub.subscribe('hot')
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for i in sub.listen():
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if isinstance(i.get('data'), str):
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if i.get('data') == 'exit':
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# worker???????????????????
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print('Gearman monitor receive restart signal.')
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GEARMAN_CONTINUE_WORK = False
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sub.unsubscribe('hot')
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break
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# ????????,?????????gearman worker????????
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except Exception as e:
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print(e)
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try:
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sub.unsubscribe('hot')
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except Exception:
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pass
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print('Gearman monitor closed')
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if __name__ == '__main__':
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def test_multi_gearman_worker(worker, job):
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print('who ', worker)
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print('do what ', job.data)
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print('Game over! ', job.data)
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return job.data
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gearman_worker = MultiGearmanWorker(('10.10.13.5:4730', ), '10.10.13.8', 6379)
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gearman_worker.register_task('test_multi_gearman_worker', test_multi_gearman_worker)
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gearman_worker.work(POLL_TIMEOUT_IN_SECONDS, 5)
注:
1. 需要先有安装好的redis;
2. 需要先有安装好的gearman
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