Only calculate slave->build mapping once in json output.

third_party/buildbot_8_4p1/README.chromium

Index: third_party/buildbot_8_4p1/README.chromium
diff --git a/third_party/buildbot_8_4p1/README.chromium b/third_party/buildbot_8_4p1/README.chromium
index 2e79182bbd5ab615c5f42cb99a42892bb386b690..02dc085785c1ffe9b2d5aae7d8b07eca87374f5b 100644
--- a/third_party/buildbot_8_4p1/README.chromium
+++ b/third_party/buildbot_8_4p1/README.chromium
@@ -2947,3 +2947,69 @@ index ed12ea0..32e1bd3 100644
 
      def __init__(self, **kwargs):
          self.factory = (self.__class__, dict(kwargs))
+
+
+diff --git a/third_party/buildbot_8_4p1/buildbot/status/web/status_json.py b/third_party/buildbot_8_4p1/buildbot/status/web/status_json.py
+index b656563..e48542d 100644
+--- a/third_party/buildbot_8_4p1/buildbot/status/web/status_json.py
++++ b/third_party/buildbot_8_4p1/buildbot/status/web/status_json.py
+@@ -16,6 +16,7 @@
+
+ """Simple JSON exporter."""
+
++import collections
+ import datetime
+ import os
+ import re
+@@ -635,21 +636,38 @@ class SlaveJsonResource(JsonResource):
+                     self.builders.append(builderName)
+         return self.builders
+
++    def getSlaveBuildMap(self, buildcache, buildercache):
++        for builderName in self.getBuilders():
++            if builderName not in buildercache:
++                buildercache.add(builderName)
++                builder_status = self.status.getBuilder(builderName)
++                for i in range(1, builder_status.buildCacheSize - 1):
++                    build_status = builder_status.getBuild(-i)
++                    if not build_status or not build_status.isFinished():
++                        # If not finished, it will appear in runningBuilds.
++                        break
++                    slave = buildcache[build_status.getSlavename()]
++                    slave.setdefault(builderName, []).append(
++                            build_status.getNumber())
++        return buildcache[self.name]
++
+     def asDict(self, request):
++        if not hasattr(request, 'custom_data'):
++            request.custom_data = {}
++        if 'buildcache' not in request.custom_data:
++            # buildcache is used to cache build information across multiple
++            # invocations of SlaveJsonResource. It should be set to an empty
++            # collections.defaultdict(dict).
++            request.custom_data['buildcache'] = collections.defaultdict(dict)
++
++            # Tracks which builders have been stored in the buildcache.
++            request.custom_data['buildercache'] = set()
++
+         results = self.slave_status.asDict()
+-        # Enhance it by adding more informations.
+-        results['builders'] = {}
+-        for builderName in self.getBuilders():
+-            builds = []
+-            builder_status = self.status.getBuilder(builderName)
+-            for i in range(1, builder_status.buildCacheSize - 1):
+-                build_status = builder_status.getBuild(-i)
+-                if not build_status or not build_status.isFinished():
+-                    # If not finished, it will appear in runningBuilds.
+-                    break
+-                if build_status.getSlavename() == self.name:
+-                    builds.append(build_status.getNumber())
+-            results['builders'][builderName] = builds
++        # Enhance it by adding more information.
++        results['builders'] = self.getSlaveBuildMap(
++                request.custom_data['buildcache'],
++                request.custom_data['buildercache'])
+         return results
+
+