zuul/releasenotes/notes/semaphores-53ff91bf6f1ad0f5.yaml
James E. Blair 153f8a90cc Support multiple semaphores
This allows jobs to request multiple semaphores.  Zuul will wait until
all are available before acquiring them* and will not start a job unless
all have been acquired.

This is useful for jobs which require access to mulitple limited resources
(especially if other jobs require access to a subset or superset of those
same resources).

* Implementation note: for efficiency, we actually do acquire them
  one-by-one but then release any which have been acquired if they are
  not all available.  This all happens very quickly within a single
  attempt to start a job.  We don't hold semaphores while we wait for
  others as that could cause deadlocks.

To be consistent with other job attributes which accept lists, this
deprecates job.semaphore and replaces it with job.semaphores.

Change-Id: I295a891a2d02b904820d8f60afe8ef862693b75d
2021-05-25 17:52:23 -07:00

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YAML

---
features:
- |
Jobs may now request multiple semaphores and they will not start until
all semaphores are acquired.
Use the new :attr:`job.semaphores` (plural) attribute to specify them.
Note that the new attribute is additive when considering
inheritance and job variants. That is to say that a job
definition with a `semaphores` attribute will extend the list of
semaphores supplied by its parent rather than overriding it (which
is the behavior for the deprecated attribute).
deprecations:
- |
The job attribute :attr:`job.semaphore` (note the singular rather
than plural form) job attribute is now deprecated. Use the plural
form :attr:`job.semaphores` instead. As with most list items in
Zuul configuration, it also accepts a single item without the
wrapping list, so to convert existing jobs, simply change the
spelling of the attribute, no change to the value is required.
The singular form will be removed in Zuul 5.0.