Enable merging buildbot builds dependent on queue length

third_party/buildbot_8_4p1/buildbot/process/builder.py

Index: third_party/buildbot_8_4p1/buildbot/process/builder.py
diff --git a/third_party/buildbot_8_4p1/buildbot/process/builder.py b/third_party/buildbot_8_4p1/buildbot/process/builder.py
index e92e2d1a34fa1e47532343f21a4beca500dd0080..b1bc75be4b42e899985d514c5a55792a728761dd 100644
--- a/third_party/buildbot_8_4p1/buildbot/process/builder.py
+++ b/third_party/buildbot_8_4p1/buildbot/process/builder.py
@@ -14,7 +14,7 @@
 # Copyright Buildbot Team Members
 
 
-import random, weakref
+import inspect, random, weakref
 from zope.interface import implements
 from twisted.python import log, failure
 from twisted.spread import pb
@@ -853,12 +853,33 @@ class Builder(pb.Referenceable, service.MultiService):
         breq_object = unclaimed_request_objects.pop(
                 unclaimed_requests.index(breq))
 
+        # Make sure the merge-requests function can take the queue length. Old

[tandrii(chromium), 2016/10/13 13:35:22]

...queue length and len(merged_requests). 

[Michael Achenbach, 2016/10/13 13:53:35]

wrote "lengths" now

+        # style functions only take two parameters.
+        mergeRequests_with_length_fn = lambda a, b, *_ : mergeRequests_fn(a, b)

[tandrii(chromium), 2016/10/13 13:35:22]

inspect on bound class functions or on functions with kwargs or *args will not
quite work in all cases as intended. I'd do the usual python way: try and see
what happens.
def wrapper(a,b,c,d):
  try:
    return mergeRequests_fn(a,b)
  except TypeError:
    return mergeRequests_fn(a,b,c,d)

[Michael Achenbach, 2016/10/13 13:53:35]

Good catch. Now implemented your suggestion to use an extra attribute and got
rid of inspect.

+        try:
+            n_args = len(inspect.getargspec(mergeRequests_fn).args)
+            if n_args > 3:
+                # New style function that accepts total and merged parameters.
+                mergeRequests_with_length_fn = mergeRequests_fn
+        except Exception as e:
+          log.err(e, 'Exception analyzing mergeRequests function.')
+
+        # This might not reflect exact number of items that could be merged
+        # (this depends on the canBeMergedWith algorithm), but it can help
+        # indicating how loaded this builder is.
+        queue_length = len(unclaimed_request_objects)
+
         # 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)))
+                    mergeRequests_with_length_fn(
+                        breq_object,
+                        other_breq_object,
+                        queue_length, 
+                        len(merged_request_objects),
+                    )))
             yield wfd
             if wfd.getResult():
                 merged_request_objects.append(other_breq_object)