Make root span trace IDs unique

CHANGELOG.md

@@ -6,6 +6,8 @@
   Use `UnknownMetricFamily` for `SumData` instead of `UntypedMetricFamily`.
   Check if label keys and values match before exporting.
 - Remove min and max from Distribution.
+- Fix a bug that caused root spans from the same tracer to share a trace ID
+  ([#505](https://github.com/census-instrumentation/opencensus-python/pull/505)
 
 ## 0.2.0
 Released 2019-01-18

opencensus/trace/tracers/context_tracer.py

@@ -16,10 +16,11 @@
 import threading
 
 from opencensus.trace import execution_context
-from opencensus.trace.span_context import SpanContext
 from opencensus.trace import span as trace_span
 from opencensus.trace import span_data as span_data_module
 from opencensus.trace.exporters import print_exporter
+from opencensus.trace.span_context import SpanContext
+from opencensus.trace.span_context import generate_trace_id
 from opencensus.trace.tracers import base
 
 
@@ -116,6 +117,8 @@ def end_span(self, *args, **kwargs):
             execution_context.set_current_span(cur_span.parent_span)
         else:
             execution_context.set_current_span(None)
+            self.span_context.trace_id = generate_trace_id()
+            self.trace_id = self.span_context.trace_id
 
         with self._spans_list_condition:
             if cur_span in self._spans_list:

tests/unit/trace/tracers/test_context_tracer.py

@@ -136,14 +136,21 @@ def test_end_span_active(self, mock_current_span):
         mock_span.attributes = {}
         mock_span.__iter__ = mock.Mock(return_value=iter([mock_span]))
         parent_span_id = '6e0c63257de34c92'
+        mock_span.parent_span = mock.Mock(spec=span.Span)
         mock_span.parent_span.span_id = parent_span_id
         mock_current_span.return_value = mock_span
+        old_trace_id = tracer.trace_id
+        self.assertEqual(tracer.trace_id, tracer.span_context.trace_id)
         tracer.end_span()
 
         self.assertTrue(mock_span.finish.called)
         self.assertEqual(tracer.span_context.span_id, parent_span_id)
         self.assertFalse(tracer.exporter.export.called)
 
+        # Check that we don't change the trace ID if the parent span exists
+        self.assertEqual(tracer.trace_id, old_trace_id)
+        self.assertEqual(tracer.trace_id, tracer.span_context.trace_id)
+
     @mock.patch.object(context_tracer.ContextTracer, 'current_span')
     def test_end_span_without_parent(self, mock_current_span):
         from opencensus.trace.execution_context import get_current_span
@@ -159,11 +166,17 @@ def test_end_span_without_parent(self, mock_current_span):
         mock_span.attributes = {}
         mock_span.__iter__ = mock.Mock(return_value=iter([mock_span]))
         mock_current_span.return_value = mock_span
+        old_trace_id = tracer.trace_id
+        self.assertEqual(tracer.trace_id, tracer.span_context.trace_id)
         tracer.end_span()
 
         cur_span = get_current_span()
         self.assertIsNone(cur_span)
 
+        # Check that ending the root span generates a new trace ID
+        self.assertNotEqual(tracer.trace_id, old_trace_id)
+        self.assertEqual(tracer.trace_id, tracer.span_context.trace_id)
+
     def test_end_span_batch_export(self):
         exporter = mock.Mock()
         tracer = context_tracer.ContextTracer(exporter=exporter)