Scheduler infinite loop after failed/canceled job

[andygrove]

Describe the bug
See PR description at #340

To Reproduce
See PR description at #340

Expected behavior
A clear and concise description of what you expected to happen.

Additional context
Add any other context about the problem here.

[mingmwang]

Ah, this is a known issue, actually I added the failed job check in the pop_next_task() loop.
Without such check, the scheduler loop will try to schedule the pending tasks from failed job which would be worse !!

@yahoNanJing
Please take a look and have a fix.

[yahoNanJing]

Thanks @andygrove and @tfeda for reporting this issue. I'll try to fix it.

[smallzhongfeng]

Any update? This will directly cause the ui to be unavailable.