[lit] Allow setting parallelism groups to None

[yln]

Summary

Check that we do not crash if a parallelism group is explicitly set to
None. Permits usage of the following pattern.

[lit.common.cfg]

lit_config.parallelism_groups['my_group'] = None
if <condition>:
  lit_config.parallelism_groups['my_group'] = 3

[project/lit.cfg]

config.parallelism_group = 'my_group'

[rnk]

lgtm

llvm/trunk/utils/lit/lit/TestingConfig.py

def load_from_path(self, path, litConfig):
                 'unable to parse config file %r, traceback: %s' % (
                     path, traceback.format_exc()))
         self.finish(litConfig)
 
     def __init__(self, parent, name, suffixes, test_format,
                  environment, substitutions, unsupported,
                  test_exec_root, test_source_root, excludes,
                  available_features, pipefail, limit_to_features = [],
-                 is_early = False, parallelism_group = ""):
+                 is_early = False, parallelism_group = None):
         self.parent = parent
         self.name = str(name)
         self.suffixes = set(suffixes)
         self.test_format = test_format
         self.environment = dict(environment)
         self.substitutions = list(substitutions)
         self.unsupported = unsupported
         self.test_exec_root = test_exec_root

llvm/trunk/utils/lit/lit/run.py

def __init__(self, display, provider, maxFailures):
         self.maxFailures = maxFailures or object()
         self.failedCount = 0
     def update(self, test):
         self.display.update(test)
         self.failedCount += (test.result.code == lit.Test.FAIL)
         if self.failedCount == self.maxFailures:
             self.provider.cancel()
 
+# No-operation semaphore for supporting `None` for parallelism_groups.
+#   lit_config.parallelism_groups['my_group'] = None
+class NopSemaphore(object):
+    def acquire(self): pass
+    def release(self): pass
+
 class Run(object):
     """
     This class represents a concrete, configured testing run.
     """
 
     def __init__(self, lit_config, tests):
         self.lit_config = lit_config
         self.tests = tests
         # Set up semaphores to limit parallelism of certain classes of tests.
-        # For example, some ASan tests require lots of virtual memory and run
-        # faster with less parallelism on OS X.
-        self.parallelism_semaphores = \
-                {k: multiprocessing.BoundedSemaphore(v) for k, v in
-                 self.lit_config.parallelism_groups.items()}
+        self.parallelism_semaphores = {
+                k : NopSemaphore() if v is None else
+                    multiprocessing.BoundedSemaphore(v)
+                for k, v in lit_config.parallelism_groups.items()}
 
     def execute_tests_in_pool(self, jobs, max_time):
         # We need to issue many wait calls, so compute the final deadline and
         # subtract time.time() from that as we go along.
         deadline = None
         if max_time:
             deadline = time.time() + max_time
 

llvm/trunk/utils/lit/tests/Inputs/parallelism-groups/lit.cfg

+import lit.formats
+config.name = 'parallelism-groups'
+config.suffixes = ['.txt']
+config.test_format = lit.formats.ShTest()
+config.test_source_root = None
+config.test_exec_root = None
+
+# Should not crash
+lit_config.parallelism_groups['my_group'] = None
+
+config.parallelism_group = 'my_group'

llvm/trunk/utils/lit/tests/Inputs/parallelism-groups/test1.txt

+# RUN: true

llvm/trunk/utils/lit/tests/Inputs/parallelism-groups/test2.txt

+# RUN: true

llvm/trunk/utils/lit/tests/parallelism-groups.py

+# Check that we do not crash if a parallelism group is set to None. Permits
+# usage of the following pattern.
+#
+# [lit.common.cfg]
+#   lit_config.parallelism_groups['my_group'] = None
+#   if <condition>:
+#     lit_config.parallelism_groups['my_group'] = 3
+#
+# [project/lit.cfg]
+#   config.parallelism_group = 'my_group'
+#
+# Note: We need at least 2 tests to prevent lit from using "single process
+#       mode", which ignores parallelism groups.
+#
+
+# RUN: %{lit} -j2 %{inputs}/parallelism-groups | FileCheck %s
+
+# CHECK:     -- Testing: 2 tests, 2 threads --
+# CHECK-DAG: PASS: parallelism-groups :: test1.txt
+# CHECK-DAG: PASS: parallelism-groups :: test2.txt
+# CHECK:     Expected Passes    : 2