Let test runner rerun failures to test for flakes.

tools/testrunner/local/execution.py

Index: tools/testrunner/local/execution.py
diff --git a/tools/testrunner/local/execution.py b/tools/testrunner/local/execution.py
index 79f856c7d7da21a4319edbd5424af557623336ec..939995cd8f112b917953d25ce4c7800b968e5150 100644
--- a/tools/testrunner/local/execution.py
+++ b/tools/testrunner/local/execution.py
@@ -81,6 +81,7 @@ class Runner(object):
     self.remaining = num_tests
     self.failed = []
     self.crashed = 0
+    self.reran_tests = 0
 
   def _RunPerfSafe(self, fun):
     try:
@@ -89,6 +90,42 @@ class Runner(object):
       print("PerfData exception: %s" % e)
       self.perf_failures = True
 
+  def _GetJob(self, test):
+    command = self.GetCommand(test)
+    timeout = self.context.timeout
+    if ("--stress-opt" in test.flags or
+        "--stress-opt" in self.context.mode_flags or
+        "--stress-opt" in self.context.extra_flags):
+      timeout *= 4
+    if test.dependency is not None:
+      dep_command = [ c.replace(test.path, test.dependency) for c in command ]
+    else:
+      dep_command = None
+    return Job(command, dep_command, test.id, timeout, self.context.verbose)
+
+  def _MaybeRerun(self, pool, test):
+    if test.run <= self.context.rerun_failures_count:
+      # Possibly rerun this test if its run count is below the maximum per
+      # test.
+      if test.run == 1:
+        # Count the overall number of reran tests on the first rerun.
+        if self.reran_tests < self.context.rerun_failures_max:
+          self.reran_tests += 1
+        else:
+          # Don't rerun this if the overall number of rerun tests has been
+          # reached.
+          return
+      if test.run >= 2 and test.duration > self.context.timeout / 20:
+        # Rerun slow tests at most once.
+        return
+
+      # Rerun this test.
+      test.duration = None
+      test.output = None
+      test.run += 1
+      pool.add([self._GetJob(test)])
+      self.remaining += 1
+
   def Run(self, jobs):
     self.indicator.Starting()
     self._RunInternal(jobs)
@@ -109,23 +146,12 @@ class Runner(object):
       assert test.id >= 0
       test_map[test.id] = test
       try:
-        command = self.GetCommand(test)
+        queue.append([self._GetJob(test)])
       except Exception, e:
         # If this failed, save the exception and re-raise it later (after
         # all other tests have had a chance to run).
         queued_exception = e
         continue
-      timeout = self.context.timeout
-      if ("--stress-opt" in test.flags or
-          "--stress-opt" in self.context.mode_flags or
-          "--stress-opt" in self.context.extra_flags):
-        timeout *= 4
-      if test.dependency is not None:
-        dep_command = [ c.replace(test.path, test.dependency) for c in command ]
-      else:
-        dep_command = None
-      job = Job(command, dep_command, test.id, timeout, self.context.verbose)
-      queue.append([job])
     try:
       it = pool.imap_unordered(RunTest, queue)
       for result in it:
@@ -143,6 +169,9 @@ class Runner(object):
           self.succeeded += 1
         self.remaining -= 1
         self.indicator.HasRun(test, has_unexpected_output)
+        if has_unexpected_output:
+          # Rerun test failures after the indicator has processed the results.
+          self._MaybeRerun(pool, test)
     finally:
       pool.terminate()
       self._RunPerfSafe(lambda: self.perf_data_manager.close())