[Buildbot] #2633: Reduce Buildset Race Condition (was: [nine] Reduce Buildset Race Condition)

[Buildbot trac]

#2633: Reduce Buildset Race Condition
------------------------+--------------------
Reporter:  dustin       |       Owner:
    Type:  enhancement  |      Status:  new
Priority:  minor        |   Milestone:  0.9.+
 Version:  master       |  Resolution:
Keywords:  simple       |
------------------------+--------------------
Changes (by dustin):

 * priority:  major => minor
 * version:   => master
 * milestone:  0.9.0 => 0.9.+


Old description:

> Make `completeBuildSet` return true if the database claims to have
> updated the row, and use that to narrow the race condition in
> `maybeBuildsetComplete`

New description:

 There's a race condition in `completeBuildset`: if two build requests
 finish at exactly the same time, on different masters, then both masters
 may run `completeBuildset` at the same time, see that the buildset is
 actually complete, and send a message indicating completion -- so,
 everyone will get two "completed" messages.

 Make `completeBuildset` return true if the database claims to have updated
 the row, and use that to narrow the race condition in
 `maybeBuildsetComplete`

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Ticket URL: <http://trac.buildbot.net/ticket/2633#comment:1>
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