Held tasks need multiple triggers to run?

[ColemanTom]

I am finding that if I have a held workflow (not paused), if I trigger a task it appears to do nothing. But, if I trigger it twice, it will then run the task. See the attached gif.

The scheduler log shows this

2024-10-08T00:42:22Z INFO - Command "force_trigger_tasks" received. ID=8b832ccb-2fba-46c7-a389-602fb984d60c
    force_trigger_tasks(flow=['all'], flow_wait=False, tasks=['20241006T1800Z/glu_ops_process_background_iasi'])
2024-10-08T00:42:22Z INFO - Command "force_trigger_tasks" actioned. ID=8b832ccb-2fba-46c7-a389-602fb984d60c
2024-10-08T00:42:22Z INFO - [20241006T1800Z/glu_ops_process_background_iasi:waiting(held)] => waiting(held)(queued)
2024-10-08T00:42:29Z INFO - Command "force_trigger_tasks" received. ID=883ccef9-4b47-4cac-9258-26056328462b
    force_trigger_tasks(flow=['all'], flow_wait=False, tasks=['20241006T1800Z/glu_ops_process_background_iasi'])
2024-10-08T00:42:29Z INFO - Command "force_trigger_tasks" actioned. ID=883ccef9-4b47-4cac-9258-26056328462b

If I read that correctly, the trigger pushes it to the queued state, and then a second trigger pushes to submit the job. I had expected that triggering would shift it twice.

I'm unsure if this is a Cylc-flow question or a UI question, so I've put it here as that is how I'm looking at it.

[hjoliver]

This is intended.

• triggering an un-queued task queues it to run
  • (we don't automatically assume that you want to violate the queue limit)
• triggering it again (i.e., triggering a queued task) causes it to submit
  • (regardless of the queue limit)

The held attribute should not make any difference here, because we can run held tasks (they should stay held to prevent any automatic retries unless released).

Are you happy with this explanation, @ColemanTom ?

[ColemanTom]

Ah, ok. So because this task is in a queue, it takes two triggers. I just tested on a task that does not belong to a queue and it does only take one. I think that there is no visible change in the WUI when I do the first trigger is part of the confusion. In Cylc7, when triggering a task which was in a full queue, it changed to (I think) a yellow colour so show the state had changed. Here, there was no update to the display.

[hjoliver]

In Cylc 8 "queued" isn't a task state, it's a particular attribute of the waiting state.

Task attributes are shown as badges on the task icon. I think we only display one badge at a time, and we prioritize held over queued, so that's why you didn't see a change in the GUI.

@cylc/core - maybe this suggests we need to stack multiple badges on task icons?

[ColemanTom]

It would be helpful to see some indication that an action has been registered and done something. I wasn't sure if it was severe lag or what was happening.

[hjoliver]

(We can close this after adding or tweaking a cylc-ui issue to cover the last comment)

[oliver-sanders]

[edit]: Dammit, this is wrong, see later comment

Aah right.

Under normal circumstances, triggering a held task DOES cause it to be run immediately, however, in this case the queue that the task was added to was full so it sat there waiting.

(We can close this after adding or tweaking a cylc-ui issue to cover the last comment)

If the queued state always beats the held state (which I think it does), then we can resolve this by changing the "task modifier" icon order from:

• is_held
• is_queued
• is_runahead

to:

• is_queued
• is_held
• is_runahead

Note, this applies both to the GUI and Tui.

Additionally, when you select a task in either, you should get a task state summary (e.g. waiting (held)). We should ensure that queued beats held here too.

And (although I agree that held isn't really a special case here) we should still give it a passing mention in the docs:

$ cylc trigger --help | grep held

TODO:

• Tui:
  • Ensure queued beets held in the task modifier icon.
  • Ensure queued beets held in the task state summary (select task and press enter).
• GUI:
  • Ensure queued beets held in the task modifier icon.
  • Ensure queued beets held in the task state summary (select task to open context menu).
• Add passing mention to held in cylc trigger CLI help?
• Add passing mention to held in cylc trigger GraphQL schema?

[oliver-sanders]

As an aside, see this snippet from the Cylc UI design document where we were exploring context information for task state modifiers:

And the [now?] erroneous statement underneath about held taking priority over queue (I guess that made sense at the time?).

Where the "view" button would have taken you to this cylc/cylc-ui#462

[oliver-sanders]

@hjoliver

Sorry, on reflection, I have realised that this was not the intended behaviour and is actually inconsistent. The current behaviour is an unintended result of a bugfix (mia-culpa) for a completely different issue.

To explain, here's the stated intention:

• Triggering an unqueued waiting task queues it, regardless of prerequisites.
• Triggering a queued task submits it, regardless of queue limiting.
• Triggering an active task has no effect (it already triggered).

cylc trigger --help

Under this logic, if you trigger a held task it will be queued. If there is space in the queue, it will run instantly.

However, at a later date, the queues because "is_held" aware in order to allow users to hold queued tasks (without us having to yank the tasks out of the queue in order to do so):

cylc-flow/cylc/flow/task_queues/independent.py

Lines 57 to 58 in 59ce660

	if itask.state.is_held:
	held.append(itask)

So a held task won't queue (naturally) and a queued held task won't run (naturally).

This changed the behaviour. Now when we trigger a held task, it gets added to the queue, but the queue will never release it (irrespective of whether there is space in the queue or not).

So the behaviour changed from "it will run when there is space in the queue" to "it will never run under any circumstances" which was not intended. Intentions aside, the "it will never run" bit is also totally illogical.

In my above comment, I made this suggestion:

If the queued state always beats the held state (which I think it does), then we can resolve this by changing the "task modifier" icon order from:

• is_held
• is_queued
• is_runahead

to:

• is_queued
• is_held
• is_runahead

However, that doesn't make sense. Under the current implementation:

• Held beats queued, because a held task cannot (naturally) become queued.
• Queued beats held, because a queued held task cannot (naturally) run.

So there is no order of precedence we can give the task modifier icon that will work in all cases, in other words, the logic is inconsistent.

To resolve this we need to either:

1. Differentiate between a held task that became queued (i.e. was manually triggered) and a queued task that became held (i.e. was manually held).
2. Remove tasks from the queue when they are manually held rather than leaving them in the queue and filtering out all held tasks.

Option (2) is nicer, and technically correct (if you hold a queued task, you are suppressing it from being submitted, so it doesn't make sense for the task to remain queued). I think it's relatively easy to do these days as we now have other functionality that needs to remove tasks from the queue (e.g. cylc remove).

[hjoliver]

I ran into a hold bug when testing this on Friday, which I'll now try to reproduce (from memory ... it was on my office box, and I'm WFH today). However, I thought it was a different issue, because @ColemanTom's description above says:

If I read that correctly, the trigger pushes it to the queued state, and then a second trigger pushes to submit the job. I had expected that triggering would shift it twice.

That's just the intended double-trigger behaviour when queue-limiting is active, which doesn't seem to gel with what you're saying @oliver-sanders ... maybe it depends on how Tom's tasks got held in the first place (e.g. were they already queued or not?).

[hjoliver]

(Side-issue spawned after taking hold and queue out of the mix: #6406 )

[ColemanTom]

Tom's tasks got held in the first place (e.g. were they already queued or not?).

I don't really remember the setup I had. If I pay attention and see it again I'll try to comment back here.

[hjoliver]

Talking a step back from attribute priority, to confirm triggering and queues work as intended without hold involved:

[scheduling]
    [[queues]]
        [[[default]]]
            limit = 1
    [[graph]]
        R1 = "foo:start => a => b"
[runtime]
    [[foo]]
        pre-script = "sleep 360"
    [[a, b]]
        script = "sleep 10; false"
        execution retry delays = PT5S

• foo:start spawns a as queued; b remains a future task

• job 01:

  • triggering a (queued) once runs it
  • triggering b once queues it; twice runs it

• job 02:

  • a queues again after retry time is done; triggering once runs it
  • b returns to waiting on a:succeeded after retry timer is done; triggering once queues it, twice runs it

  All good ✔️ (but see Triggered future tasks, and prerequisite status? #6406)

[hjoliver]

Now see how hold affects the active (n=0) waiting task a:

• hold a:waiting(queued) => a:waiting(held)(queued)
• trigger unqueues it to run (still held)
• job fails => a:waiting(held) (not queued)
• release => waiting(queued)
• (now trigger once to unqueue and run job 02)

This kinda seems right from a manual triggering perspective, IF we think that manually triggering a held task should make it and remain held - which seems reasonable because we can hold a running task, which just means it won't automatically retry.

But maybe not from an automatic triggering perspective, because a held task cannot submit a job automatically, so arguably it should not be queued? 🤔

[hjoliver]

Now see how hold affects the future task b:

• hold adds it to the future hold list
• trigger => waiting(queued) - (the hold list is not used?)
• trigger again runs it
• job 01 fails; after the retry timer it is waiting, not held and not queued

Alternatively:

• hold adds it to the future hold list
• cylc set -p 1/a causes it to spawn naturally => waiting(held) - or trigger a and allow it to succeed - (the hold list is used)
• triggering it now => b:waiting(held)(queued)

(Then same as for the a case above)