Enable merging buildbot builds dependent on queue length

third_party/buildbot_8_4p1/buildbot/process/builder.py

 # This file is part of Buildbot.  Buildbot is free software: you can
 # redistribute it and/or modify it under the terms of the GNU General Public
 # License as published by the Free Software Foundation, version 2.
 #
 # This program is distributed in the hope that it will be useful, but WITHOUT
 # ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 # FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
 # details.
 #
 # You should have received a copy of the GNU General Public License along with
@@ skipping 838 matching lines @@
                 [ self._brdictToBuildRequest(brdict)
                   for brdict in unclaimed_requests ]))
         yield wfd
         unclaimed_request_objects = wfd.getResult()
         breq_object = unclaimed_request_objects.pop(
                 unclaimed_requests.index(breq))
 
         # gather the mergeable requests
         merged_request_objects = [breq_object]
         for other_breq_object in unclaimed_request_objects:
-            wfd = defer.waitForDeferred(
-                defer.maybeDeferred(lambda :
-                    mergeRequests_fn(breq_object, other_breq_object)))
+            if getattr(mergeRequests_fn, 'with_length', False):
+                # If supported, we also pass the number of unclaimed and
+                # the number of already merged builds. The first might not
+                # reflect the exact number that could be merged (this
+                # depends on the canBeMergedWith algorithm), but it can help
+                # indicating how loaded this builder is.
+                to_defer = lambda : mergeRequests_fn(
+                    breq_object,
+                    other_breq_object,
+                    len(unclaimed_request_objects), 
+                    len(merged_request_objects),
+                )
+            else:
+                to_defer = lambda : mergeRequests_fn(
+                    breq_object,
+                    other_breq_object,
+                )
+            wfd = defer.waitForDeferred(defer.maybeDeferred(to_defer))
             yield wfd
             if wfd.getResult():
                 merged_request_objects.append(other_breq_object)
 
         # convert them back to brdicts and return
         merged_requests = [ br.brdict for br in merged_request_objects ]
         yield merged_requests
 
     def _brdictToBuildRequest(self, brdict):
         """
@@ skipping 107 matching lines @@
         d = defer.DeferredList(dl)
         d.addCallback(self._gatherPingResults)
         return d
 
     def _gatherPingResults(self, res):
         for ignored,success in res:
             if not success:
                 return False
         return True