[Buildbot-commits] [Buildbot] #2249: change merging is no longer picking the newest change

[Buildbot]

#2249: change merging is no longer picking the newest change
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Reporter:  dustin  |       Owner:
    Type:  defect  |      Status:  new
Priority:  major   |   Milestone:  0.8.7
 Version:  0.8.6   |  Resolution:
Keywords:          |
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Changes (by dustin):

 * milestone:  0.8.6 => 0.8.7


Comment:

 I can't reproduce this externally.  I'm using a sendchange loop to send
 changes every 2s for a 5s build, and the changes come out in the right
 order, and with the right revision.

 Here's what I've got so far, from the db:

  * Changes 4011 and 4012 were placed in the same sourcestamp (1976) due to
 a tree stable timer.  Change 4013 was in its own sourcestamp (1977).
  * Buildset 1980 points to ss 1976, and buildset 1981 points to ss 1977
  * os-leopard !BuildRequest 42880 points to buildset 1980, and 42922
 points to buildset 1981.

 The build-starting process looks like this:
  * in `maybeStartBuild`, `unclaimed_requests = [ <br 42880>, <br 42922> ]`
 (sorted by the buildsets' `submitted_at`)
  * it calls `_chooseBuild`, which simply returns the first - `<br 42880>`
  * that gets merged with br 42922
  * `Build()` gets called with `[ <br 42880>, <br 42922> ]`
  * it sets its `.source` to `<br 42880>.mergeWith([<br 42922>])`
  * ..which calls `SourceStamp.mergeWith`
  * ..which concatenates the changes as `<br 42880>.changes + <br
 42922>.changes`, or `[ <ch 4011>, <ch 4012>, <ch 4013> ]`
  * ..and calls the `SourceStamp` constructor, which gets the revision from
 the last change, and thus should get change 4013's revision.

 Clearly, something did not happen as expected here: by the time
 `SourceStamp.mergeWith` got called, the build requests were in the wrong
 order.  So either unclaimed_requests is not sorted correctly, or
 `_chooseBuild` is misbehaving, or the merging is re-ordering things.

 All of those seem pretty bulletproof.  `unclaimed_requests` is properly
 sorted - I tested by shuffling the list before sorting.  `_chooseBuild`
 just returns `[0]`.   And while `_mergeRequests` does use `gatherResults`,
 it does so in a fashion that correctly maintains order - I tested by
 adding a random delay to each `_brdictToBuildRequest` invocation.

 So I'm at a loss to figure out what went wrong here.  Which means I can't
 fix it for 0.8.6 without more evidence.

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Ticket URL: <http://trac.buildbot.net/ticket/2249#comment:2>
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