Respect max-substitution-jobs again (backport #11402) #11408
Merged
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Motivation
This broke in #11005. Any number of
PathSubstitutionGoals
would be woken up by a single build slot becoming available. If there are a lot of substitution goals active, this could lead to us running out of file descriptors (especially on macOS where the default limit is 256).Note: we have a bit of a thundering herd problem here, since it's pretty inefficient to wake up potentially hundreds of goals, most of which will immediately go to sleep again. Ideally
waitForBuildSlot()
would wake up only one co-routine of the right type.Context
Priorities and Process
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This is an automatic backport of pull request #11402 done by [Mergify](https://mergify.com).