Task that depends on multiple wall_clock xtriggers will submit when first is satisfied

[MetRonnie]

Reproducible Example

Weird example but demonstrates the bug

[scheduler]
    allow implicit tasks = True
[scheduling]
    initial cycle point = 2018-01-01
    [[xtriggers]]
        clock_1 = wall_clock()  # satisfied when now > 2018-01-01
        clock_2 = wall_clock(offset=P10Y)  # satisfied when now > 2028-01-01
    [[graph]]
        R1 = @clock_1 & @clock_2 => foo

INFO - [20180101T0000Z/foo waiting(runahead) job:00 flows:1] => waiting
INFO - xtrigger satisfied: clock_1 = wall_clock(trigger_time=1514764800)
INFO - xtrigger satisfied: clock_2 = wall_clock(trigger_time=1514764800) <-- note same trigger time logged
...
INFO - [20180101T0000Z/foo preparing job:01 flows:1] => submitted

Expected Behaviour

foo only submits when all the wall_clock xtriggers it depends on are satisfied.

Additional Context

I think the log is wrong - I don't think clock_2 is satisfied yet; it's just ignored by foo. If you change it to

R1 = """
   @clock_1 & clock_2 => foo
   @clock_2 => bar
"""

then foo still submits immediately but bar does not submit yet

[wxtim]

This is caused by itask.get_clock_trigger_time caching the clock trigger time, causing it to return the first value it was ever fed every time.

Can we safely not cache this?

[oliver-sanders]

Closed by #5791