See my Cancel old hanging python3Y CI builds issue.

It would be good if old hanging builds were cancelled after a PR is closed/merged.

The only problem I see that maybe somebody has merged a PR, yet waits for the scratch build to finish. For that reason, I suppose 24 hours long grace period should work fine in most cases.

I see 2 ways to do that:

• a garbage collector cronjob that goes trough all the still running builds and checks if (is closed or is merged) and is older than 1 day -> cancel.
• a scheduler that schedules a cancel 24 hours into the future once it receives a fedmsg about PR being closed/merged.