Update the should_sample logic for tracer (#166)

Author: liyanhui1228

opencensus/trace/trace_options.py

@@ -59,3 +59,14 @@ def get_enabled(self):
         enabled = bool(int(self.trace_options_byte) & _ENABLED_BITMASK)
 
         return enabled
+
+    def set_enabled(self, enabled):
+        """Update the last bit of the trace options byte str.
+
+        :type enabled: bool
+        :param enabled: Whether enable tracing in this span context or not.
+        """
+        enabled_bit = '1' if enabled else '0'
+        self.trace_options_byte = str(
+            self.trace_options_byte)[:-1] + enabled_bit
+        self.enabled = self.get_enabled

opencensus/trace/tracer.py

@@ -67,20 +67,21 @@ def __init__(
 
     def should_sample(self):
         """Determine whether to sample this request or not.
-        If the context forces not tracing, just set enabled to False.
-        Else follow the sampler.
+        If the context enables tracing, return True.
+        Else follow the decision of the sampler.
 
         :rtype: bool
         :returns: Whether to trace the request or not.
         """
         return self.span_context.trace_options.enabled \
-            and self.sampler.should_sample(self.span_context.trace_id)
+            or self.sampler.should_sample(self.span_context.trace_id)
 
     def get_tracer(self):
         """Return a tracer according to the sampling decision."""
         sampled = self.should_sample()
 
         if sampled:
+            self.span_context.trace_options.set_enabled(True)
             return context_tracer.ContextTracer(
                 exporter=self.exporter,
                 span_context=self.span_context)

tests/unit/trace/test_tracer.py

@@ -48,6 +48,7 @@ def test_constructor_explicit(self):
         exporter = mock.Mock()
         propagator = mock.Mock()
         span_context = mock.Mock()
+        span_context.trace_options.enabled = False
 
         tracer = tracer_module.Tracer(
             span_context=span_context,
@@ -65,8 +66,10 @@ def test_should_sample_force_not_trace(self):
 
         span_context = mock.Mock()
         span_context.trace_options.enabled = False
+        sampler = mock.Mock()
+        sampler.should_sample.return_value = False
         tracer = tracer_module.Tracer(
-            span_context=span_context)
+            span_context=span_context, sampler=sampler)
         sampled = tracer.should_sample()
 
         self.assertFalse(sampled)
@@ -82,7 +85,10 @@ def test_should_sample_sampled(self):
     def test_should_sample_not_sampled(self):
         sampler = mock.Mock()
         sampler.should_sample.return_value = False
-        tracer = tracer_module.Tracer(sampler=sampler)
+        span_context = mock.Mock()
+        span_context.trace_options.enabled = False
+        tracer = tracer_module.Tracer(
+            span_context=span_context, sampler=sampler)
         sampled = tracer.should_sample()
 
         self.assertFalse(sampled)
@@ -108,13 +114,17 @@ def get_tracer_context_tracer(self):
         result = tracer.get_tracer()
 
         assert isinstance(result, context_tracer.ContextTracer)
+        self.assertTrue(tracer.span_context.trace_options.enabled)
 
     def test_finish_not_sampled(self):
         from opencensus.trace.tracers import noop_tracer
 
         sampler = mock.Mock()
         sampler.should_sample.return_value = False
-        tracer = tracer_module.Tracer(sampler=sampler)
+        span_context = mock.Mock()
+        span_context.trace_options.enabled = False
+        tracer = tracer_module.Tracer(
+            span_context=span_context, sampler=sampler)
         assert isinstance(tracer.tracer, noop_tracer.NoopTracer)
         mock_tracer = mock.Mock()
         tracer.tracer = mock_tracer
@@ -138,12 +148,16 @@ def test_span_not_sampled(self):
 
         sampler = mock.Mock()
         sampler.should_sample.return_value = False
-        tracer = tracer_module.Tracer(sampler=sampler)
+        span_context = mock.Mock()
+        span_context.trace_options.enabled = False
+        tracer = tracer_module.Tracer(
+            span_context=span_context, sampler=sampler)
 
         span = tracer.span()
 
         # Test nested span not sampled
         child_span = span.span()
+        tracer.finish()
 
         assert isinstance(span, base.NullContextManager)
         assert isinstance(child_span, base.NullContextManager)
@@ -164,7 +178,10 @@ def test_start_span_not_sampled(self):
 
         sampler = mock.Mock()
         sampler.should_sample.return_value = False
-        tracer = tracer_module.Tracer(sampler=sampler)
+        span_context = mock.Mock()
+        span_context.trace_options.enabled = False
+        tracer = tracer_module.Tracer(
+            span_context=span_context, sampler=sampler)
 
         span = tracer.start_span()
 
@@ -184,6 +201,7 @@ def test_end_span_not_sampled(self):
         sampler = mock.Mock()
         sampler.should_sample.return_value = False
         span_context = mock.Mock()
+        span_context.trace_options.enabled = False
         tracer = tracer_module.Tracer(
             sampler=sampler,
             span_context=span_context)
@@ -220,7 +238,10 @@ def test_current_span_not_sampled(self):
 
         sampler = mock.Mock()
         sampler.should_sample.return_value = False
-        tracer = tracer_module.Tracer(sampler=sampler)
+        span_context = mock.Mock()
+        span_context.trace_options.enabled = False
+        tracer = tracer_module.Tracer(
+            sampler=sampler, span_context=span_context)
 
         span = tracer.current_span()
 
@@ -244,7 +265,10 @@ def test_add_attribute_to_current_span_not_sampled(self):
 
         sampler = mock.Mock()
         sampler.should_sample.return_value = False
-        tracer = tracer_module.Tracer(sampler=sampler)
+        span_context = mock.Mock()
+        span_context.trace_options.enabled = False
+        tracer = tracer_module.Tracer(
+            span_context=span_context, sampler=sampler)
         tracer.add_attribute_to_current_span('key', 'value')
 
         span = tracer.current_span()