CrossValidation & co.: handle internal cross-validation

Author: kernc

Orange/evaluation/testing.py

@@ -331,6 +331,12 @@ def _is_picklable(obj):
             warnings.warn("Not all arguments (learners) are picklable. "
                           "Setting n_jobs=1", OrangeWarning)
 
+        if n_jobs > 1 and mp.current_process().daemon:
+            n_jobs = 1
+            warnings.warn("Worker subprocesses cannot spawn new worker "
+                          "subprocesses (e.g. parameter tuning with internal "
+                          "cross-validation). Setting n_jobs=1", OrangeWarning)
+
         # Workaround for NumPy locking on Macintosh.
         # https://pythonhosted.org/joblib/parallel.html#bad-interaction-of-multiprocessing-and-third-party-libraries
         mp_ctx = mp.get_context(

Orange/tests/test_evaluation_testing.py

@@ -29,6 +29,13 @@ def test_no_data(self):
                           learners=[NaiveBayesLearner()])
 
 
+class _ParameterTuningLearner(MajorityLearner):
+    def __call__(self, data):
+        learner = MajorityLearner()
+        CrossValidation(data, [learner], k=2)
+        return learner(data)
+
+
 # noinspection PyUnresolvedReferences
 class CommonSamplingTests(unittest.TestCase):
     @classmethod
@@ -210,6 +217,9 @@ class NonPicklableLearner(MajorityLearner):
         self.assertWarns(OrangeWarning,
                          CrossValidation, self.iris, [NonPicklableLearner()], k=3)
 
+    def test_internal_cv(self):
+        # This test just covers; can't catch warnings from subprocesses
+        CrossValidation(self.iris, [_ParameterTuningLearner()], k=2)
 
 class LeaveOneOutTestCase(CommonSamplingTests):
     def test_results(self):