[Buildbot-devel] Assert failure when using SlaveLocks

[Kinneberg, Steve]

My appologies if anyone gets this twice.  Had trouble sending it earlier.

I keep encountering the following assert fail when I use SlaveLocks to limit the number of builds a slave performs at a time.  I've attached a simple master.cfg that can reproduce the problem.  Our real config is sufficiently complex enough that we can't set maxBuilds = 1 for the slaves, so we are using SlaveLocks instead for certain builders.

The situation is when several builds are triggered to run so that they are running concurrently, then the order the builds actually run gets confused and triggers the following assert fail:

2008/10/02 16:09 -0700 [-] Unhandled error in Deferred:
2008/10/02 16:09 -0700 [-] Unhandled Error
        Traceback (most recent call last):
          File "/usr/lib/python2.5/site-packages/twisted/internet/defer.py", line 182, in addCallbacks
            self._runCallbacks()
          File "/usr/lib/python2.5/site-packages/twisted/internet/defer.py", line 317, in _runCallbacks
            self.result = callback(self.result, *args, **kw)
          File "/usr/lib/python2.5/site-packages/twisted/internet/defer.py", line 281, in _continue
            self.unpause()
          File "/usr/lib/python2.5/site-packages/twisted/internet/defer.py", line 277, in unpause
            self._runCallbacks()
        --- <exception caught here> ---
          File "/usr/lib/python2.5/site-packages/twisted/internet/defer.py", line 317, in _runCallbacks
            self.result = callback(self.result, *args, **kw)
          File "/home/stevek/lib/python/buildbot/process/base.py", line 366, in _startBuild_2
            self.build_status.buildStarted(self)
          File "/home/stevek/lib/python/buildbot/status/builder.py", line 1149, in buildStarted
            self.builder.buildStarted(self)
          File "/home/stevek/lib/python/buildbot/status/builder.py", line 1674, in buildStarted
            assert s.number == self.nextBuildNumber - 1
        exceptions.AssertionError:

With the attached master.cfg file this assert fail can be easily triggered by issuing 3 sendchanges in a row 2 seconds apart.

Would it be safe to remove that assert or change it to verify that the s.number is simply less than self.nextBuildNumber since the builds are not happening in order due to the SlaveLock?

I've seen this problem with 0.7.8 and 0.7.9, and I suspect that it has been around for a longer period of time.

Thanks,
Steve
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