make context propagation robust to unavailability of root tracer

contrib/opencensus-ext-threading/opencensus/ext/threading/trace.py

@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+
 import logging
 import threading
 from concurrent import futures
@@ -88,8 +89,14 @@ def wrap_apply_async(apply_async_func):
     that will be called and wrap it then add the opencensus context."""
 
     def call(self, func, args=(), kwds={}, **kwargs):
-        wrapped_func = wrap_task_func(func)
         _tracer = execution_context.get_opencensus_tracer()
+
+        from opencensus.trace.tracers.noop_tracer import NoopTracer
+
+        if isinstance(_tracer, NoopTracer):
+            return apply_async_func(self, func, args=args, kwds={}, **kwargs)
+
+        wrapped_func = wrap_task_func(func)
         propagator = binary_format.BinaryFormatPropagator()
 
         wrapped_kwargs = {}
@@ -113,14 +120,21 @@ def wrap_submit(submit_func):
     that will be called and wrap it then add the opencensus context."""
 
     def call(self, func, *args, **kwargs):
-        wrapped_func = wrap_task_func(func)
         _tracer = execution_context.get_opencensus_tracer()
+
+        from opencensus.trace.tracers.noop_tracer import NoopTracer
+
+        if isinstance(_tracer, NoopTracer):
+            return submit_func(self, func, *args, **kwargs)
+
+        wrapped_func = wrap_task_func(func)
         propagator = binary_format.BinaryFormatPropagator()
 
         wrapped_kwargs = {}
         wrapped_kwargs["span_context_binary"] = propagator.to_header(
             _tracer.span_context
         )
+
         wrapped_kwargs["kwds"] = kwargs
         wrapped_kwargs["sampler"] = _tracer.sampler
         wrapped_kwargs["exporter"] = _tracer.exporter

contrib/opencensus-ext-threading/tests/test_noop_tracer.py

@@ -0,0 +1,50 @@
+import unittest
+from unittest.mock import patch, MagicMock
+
+from opencensus.trace.tracers.noop_tracer import NoopTracer
+from opencensus.ext.threading.trace import wrap_submit, wrap_apply_async
+
+
+class TestNoopTracer(unittest.TestCase):
+    """
+    In case no OpenCensus context is present (i.e. we have a NoopTracer), do _not_ pass down tracer in apply_async
+    and submit; instead invoke function directly.
+    """
+
+    @patch("opencensus.ext.threading.trace.wrap_task_func")
+    @patch("opencensus.trace.execution_context.get_opencensus_tracer")
+    def test_noop_tracer_apply_async(
+        self, get_opencensus_tracer_mock: MagicMock, wrap_task_func_mock: MagicMock
+    ):
+        mock_tracer = NoopTracer()
+        get_opencensus_tracer_mock.return_value = mock_tracer
+        submission_function_mock = MagicMock()
+        original_function_mock = MagicMock()
+
+        wrap_apply_async(submission_function_mock)(None, original_function_mock)
+
+        # check whether invocation of original function _has_ happened
+        submission_function_mock.assert_called_once_with(
+            None, original_function_mock, args=(), kwds={}
+        )
+
+        # ensure that the function has _not_ been wrapped
+        wrap_task_func_mock.assert_not_called()
+
+    @patch("opencensus.ext.threading.trace.wrap_task_func")
+    @patch("opencensus.trace.execution_context.get_opencensus_tracer")
+    def test_noop_tracer_wrap_submit(
+        self, get_opencensus_tracer_mock: MagicMock, wrap_task_func_mock: MagicMock
+    ):
+        mock_tracer = NoopTracer()
+        get_opencensus_tracer_mock.return_value = mock_tracer
+        submission_function_mock = MagicMock()
+        original_function_mock = MagicMock()
+
+        wrap_submit(submission_function_mock)(None, original_function_mock)
+
+        # check whether invocation of original function _has_ happened
+        submission_function_mock.assert_called_once_with(None, original_function_mock)
+
+        # ensure that the function has _not_ been wrapped
+        wrap_task_func_mock.assert_not_called()

contrib/opencensus-ext-threading/tests/test_tracer.py

@@ -0,0 +1,72 @@
+import unittest
+from unittest.mock import patch, MagicMock
+from opencensus.ext.threading.trace import wrap_submit, wrap_apply_async
+
+
+class TestTracer(unittest.TestCase):
+    """
+    Ensures that sampler, exporter, propagator are passed through
+    in case global tracer is present.
+    """
+
+    @patch("opencensus.trace.propagation.binary_format.BinaryFormatPropagator")
+    @patch("opencensus.ext.threading.trace.wrap_task_func")
+    @patch("opencensus.trace.execution_context.get_opencensus_tracer")
+    def test_apply_async_context_passed(
+        self,
+        get_opencensus_tracer_mock: MagicMock,
+        wrap_task_func_mock: MagicMock,
+        binary_format_propagator_mock: MagicMock,
+    ):
+        mock_tracer = NoNoopTracerMock()
+        # ensure that unique object is generated
+        mock_tracer.sampler = MagicMock()
+        mock_tracer.exporter = MagicMock()
+        mock_tracer.propagator = MagicMock()
+
+        get_opencensus_tracer_mock.return_value = mock_tracer
+
+        submission_function_mock = MagicMock()
+        original_function_mock = MagicMock()
+
+        wrap_apply_async(submission_function_mock)(None, original_function_mock)
+
+        # check whether invocation of original function _has_ happened
+        call = submission_function_mock.call_args_list[0].kwargs
+
+        self.assertEqual(id(call["kwds"]["sampler"]), id(mock_tracer.sampler))
+        self.assertEqual(id(call["kwds"]["exporter"]), id(mock_tracer.exporter))
+        self.assertEqual(id(call["kwds"]["propagator"]), id(mock_tracer.propagator))
+
+    @patch("opencensus.trace.propagation.binary_format.BinaryFormatPropagator")
+    @patch("opencensus.ext.threading.trace.wrap_task_func")
+    @patch("opencensus.trace.execution_context.get_opencensus_tracer")
+    def test_wrap_submit_context_passed(
+        self,
+        get_opencensus_tracer_mock: MagicMock,
+        wrap_task_func_mock: MagicMock,
+        binary_format_propagator_mock: MagicMock,
+    ):
+        mock_tracer = NoNoopTracerMock()
+        # ensure that unique object is generated
+        mock_tracer.sampler = MagicMock()
+        mock_tracer.exporter = MagicMock()
+        mock_tracer.propagator = MagicMock()
+
+        get_opencensus_tracer_mock.return_value = mock_tracer
+
+        submission_function_mock = MagicMock()
+        original_function_mock = MagicMock()
+
+        wrap_submit(submission_function_mock)(None, original_function_mock)
+
+        # check whether invocation of original function _has_ happened
+        call = submission_function_mock.call_args_list[0].kwargs
+
+        self.assertEqual(id(call["sampler"]), id(mock_tracer.sampler))
+        self.assertEqual(id(call["exporter"]), id(mock_tracer.exporter))
+        self.assertEqual(id(call["propagator"]), id(mock_tracer.propagator))
+
+
+class NoNoopTracerMock(MagicMock):
+    pass