Avoid collisions in temporary directory names

run/src/master/master.cfg

@@ -144,13 +144,19 @@ trigger_factory = util.BuildFactory(
     chunked_steps
 )
 
-chunk_result_dir_name = util.Interpolate('/'.join([
-    '..', 'chunk-results', '%(prop:revision)s', '%(prop:browser_name)s'
-]))
-chunk_result_file_name = util.Interpolate('/'.join([
-    '..', 'chunk-results', '%(prop:revision)s', '%(prop:browser_name)s',
+# It is possible that no commits are merged to the `master` branch of the Web
+# Platform tests project between two regularly-scheduled occurrences of the
+# "Initiator" builder. In order to prevent collision of temporary data storage
+# locations in these cases, special care should be taken to ensure that
+# distinct "chunk results" directory names are used. This is accomplished below
+# by including the identifier of the "Initiator" build.
+chunk_result_dir_name = util.Interpolate(
+    '../chunk-results/%(prop:results_id)s'
+)
+chunk_result_file_name = util.Interpolate(
+    '../chunk-results/%(prop:results_id)s/' +
     '%(prop:this_chunk)s_of_%(prop:total_chunks)s.json'
-]))
+)
 chunked_factory = util.BuildFactory([
     steps.Git(repourl='git://github.com/w3c/web-platform-tests'),
     temp_dir.CreateStep(name='Create temporary directory'),
@@ -195,7 +201,8 @@ chunked_factory = util.BuildFactory([
                               'browser_version': util.Property('browser_version'),
                               'os_name': util.Property('os_name'),
                               'os_version': util.Property('os_version'),
-                              'revision_date': util.Property('revision_date')
+                              'revision_date': util.Property('revision_date'),
+                              'results_id': util.Property('results_id')
                           })
 ])
 

run/src/master/wpt_chunked_step.py

@@ -19,7 +19,10 @@ def __init__(self, platform_id, platform, total_chunks, *args, **kwargs):
 
     def getSchedulersAndProperties(self):
         spec = []
+        revision = self.build.properties.getProperty('got_revision')
         revision_date = self.build.properties.getProperty('revision_date')
+        browser_name = self.platform['browser_name']
+        results_id = '%s-%s-%s' % (browser_name, revision, self.build.buildid)
 
         for scheduler in self.schedulerNames:
             unimportant = scheduler in self.unimportantSchedulerNames
@@ -31,12 +34,13 @@ def getSchedulersAndProperties(self):
                         'this_chunk': this_chunk,
                         'total_chunks': self.total_chunks,
                         'platform_id': self.platform_id,
-                        'browser_name': self.platform['browser_name'],
+                        'browser_name': browser_name,
                         'browser_version': self.platform['browser_version'],
                         'os_name': self.platform['os_name'],
                         'os_version': self.platform['os_version'],
                         'use_sauce_labs': self.platform.get('sauce', False),
-                        'revision_date': revision_date
+                        'revision_date': revision_date,
+                        'results_id': results_id
                     },
                     'unimportant': unimportant
                 })

run/src/master/wpt_detect_complete_step.py

@@ -15,15 +15,12 @@ def __init__(self, *args, **kwargs):
         super(WptDetectCompleteStep, self).__init__(*args, **kwargs)
 
     def allResultsPresent(self, step):
-        browser_name = self.build.properties.getProperty('browser_name')
-        revision = self.build.properties.getProperty('revision')
         total_chunks = self.build.properties.getProperty('total_chunks')
         chunk_results_dir = os.path.sep.join([
             os.path.abspath(os.path.dirname(__file__)),
             '..',
             'chunk-results',
-            revision,
-            browser_name
+            self.build.properties.getProperty('results_id')
         ])
         actual = set(os.listdir(chunk_results_dir))
         expected = set(