Only run one job concurrently in apscheduler across the same scheduler
<p>I'm trying to ensure that only one job is run at a time in the same scheduler. So for example, I may have something like this:</p>

<pre><code>def echo_arg(arg):
  print 'Going to tell you the arg! The arg is: {0}'.format(arg)
  sleep(5)

def main():
  scheduler = BlockingScheduler()
  for i in range(0, 60):
      scheduler.add_job(echo_arg, 'cron', args=[i], second=i, max_instances=1)
  scheduler.start()
</code></pre>

<p>Even though there are 60 distinct <em>jobs</em>, I'd like the scheduler to block until the previous job has completed. For example, the job at 0 seconds should render the runs at 1, 2, 3, and 4 invalid. Is there some way to do this in the scheduler itself?</p>

<p>Thanks!</p>