apscheduler提示maximum错误

起因

在tornado中用apscheduler实现计划任务，出现错误提示 “maximum number of running instances reached (1)”

2015-12-04 19:10:22,227 - apscheduler.scheduler - WARNING - Execution of job "TaskHandle.progress_job (trigger: date[2015-12-04 19:10:22 CST], next run at: 2015-12-04 19:10:22 CST)" skipped: 

分析

缺乏资料，所以根据提示，分析apscheduler源码

• 记录异常位置
  在源码目录下，搜索关键字maxinum，找到记录异常的位置

#apscheduler/schedulers/base.pyif run_times:    try:        executor.submit_job(job, run_times)    except MaxInstancesReachedError:        self._logger.warning(            'Execution of job "%s" skipped: maximum number of running instances reached (%d)',            job, job.max_instances)    except:        self._logger.exception('Error submitting job "%s" to executor "%s"', job, job.executor)

• 异常抛出位置

继续看submit_job函数，找到异常抛出位置

#apscheduler/executors/base.pydef submit_job(self, job, run_times):    """    Submits job for execution.    :param Job job: job to execute    :param list[datetime] run_times: list of datetimes specifying when the job should have been run    :raises MaxInstancesReachedError: if the maximum number of allowed instances for this job has been reached    """    assert self._lock is not None, 'This executor has not been started yet'    with self._lock:        if self._instances[job.id] >= job.max_instances:            raise MaxInstancesReachedError(job)        self._do_submit_job(job, run_times)        self._instances[job.id] += 1

• _instances变量作用
  在submit_job(提交任务)时加1，在_run_job_success(任务运行成功)时减1。 当self._instances[job.id]大于job.max_instances抛出异常。
  max_instances默认值为1，它表示id相同的任务实例数。

解决

通过设置max_instances参数

sched.add_job(child_job, max_instances=10, trigger=DateTrigger(), id="123")

重现脚本

import timeimport tornado.ioloopfrom apscheduler.triggers.date import DateTriggerfrom apscheduler.schedulers.tornado import TornadoSchedulersched = TornadoScheduler()def child_job():    print "start"    time.sleep(60)    print "end"def main_job():    sched.add_job(child_job, trigger=DateTrigger(), id="123")sched.add_job(main_job, 'interval', seconds=5)sched.start()tornado.ioloop.IOLoop.instance().start()

• 输出

job_id: 7279209ab6c2498698f2117bb97e18a1, instances: 0, max_instances: 1job_id: 123, instances: 0, max_instances: 1startjob_id: 7279209ab6c2498698f2117bb97e18a1, instances: 0, max_instances: 1job_id: 123, instances: 1, max_instances: 1WARNING:apscheduler.scheduler:Execution of job "child_job (trigger: date[2015-12-07 15:27:11 CST], next run at: 2015-12-07 15:27:11 CST)" skipped: maximum number of running instances reached (1)job_id: 7279209ab6c2498698f2117bb97e18a1, instances: 0, max_instances: 1