mixed parentless/non-parentless task cause premature shutdown about cylc-flow HOT 8 OPEN

My minimal example:

[scheduling]
    cycling mode = integer
    [[graph]]
        P2 = "a => b"
        2/P2 = """
           a => b
           b[-P1] => a
         """
[runtime]
    [[a,b]]

Actually, even this:

[scheduling]
    cycling mode = integer
    [[graph]]
        P2 = "a"
        2/P2 = "a[-P1] => a"
[runtime]
    [[a]]

These both shut down after point 6.

from cylc-flow.

I think the clock trigger is unnecessary, to reproduce this @dwsutherland ?

from cylc-flow.

And for me, it shuts down prematurely after the 2015 point, but I haven't seen it stall. (Mind you, premature shut down is even worse!)

from cylc-flow.

For reference. Fortunately this sort of alternating parented/parentless structure is probably unlikely in real workflows.

from cylc-flow.

I think the clock trigger is unnecessary, to reproduce this @dwsutherland ?

Yes, mentioned that

from cylc-flow.

Sorry, so you did! 🤦

from cylc-flow.

And for me, it shuts down prematurely after the 2015 point, but I haven't seen it stall. (Mind you, premature shut down is even worse!)

Yes, sorry, fixed description

from cylc-flow.

I think the trouble occurs when a non-parentless task ends up the final or next at the runahead limit.

I think you might be right there...

from cylc-flow.