Integrate tracer with context (#86)

README.md

@@ -6,6 +6,26 @@
 
 The Python [OpenTelemetry](https://opentelemetry.io/) client.
 
+## Installation
+
+## Usage
+```python
+from opentelemetry import trace
+from opentelemetry.context import Context
+from opentelemetry.sdk.trace import Tracer
+
+trace.set_preferred_tracer_implementation(lambda T: Tracer())
+tracer = trace.tracer()
+with tracer.start_span('foo'):
+    print(Context)
+    with tracer.start_span('bar'):
+        print(Context)
+        with tracer.start_span('baz'):
+            print(Context)
+        print(Context)
+    print(Context)
+```
+
 ## Contributing
 
 See [CONTRIBUTING.md](CONTRIBUTING.md)

opentelemetry-api/src/opentelemetry/context/base_context.py

@@ -64,11 +64,9 @@ def register_slot(
         :returns: The registered slot.
         """
         with cls._lock:
-            if name in cls._slots:
-                raise ValueError('slot {} already registered'.format(name))
-            slot = cls.Slot(name, default)
-            cls._slots[name] = slot
-            return slot
+            if name not in cls._slots:
+                cls._slots[name] = cls.Slot(name, default)
+            return cls._slots[name]
 
     def apply(self, snapshot: typing.Dict[str, 'object']) -> None:
         """Set the current context from a given snapshot dictionary"""
@@ -97,6 +95,12 @@ def __setattr__(self, name: str, value: 'object') -> None:
         slot = self._slots[name]
         slot.set(value)
 
+    def __getitem__(self, name: str) -> 'object':
+        return self.__getattr__(name)
+
+    def __setitem__(self, name: str, value: 'object') -> None:
+        self.__setattr__(name, value)
+
     def with_current_context(
             self,
             func: typing.Callable[..., 'object'],

opentelemetry-sdk/src/opentelemetry/sdk/trace/__init__.py

@@ -17,13 +17,13 @@
 from collections import deque
 from collections import namedtuple
 from contextlib import contextmanager
-import contextvars
 import random
 import threading
 import typing
 
 from opentelemetry import trace as trace_api
 from opentelemetry import types
+from opentelemetry.context import Context
 from opentelemetry.sdk import util
 
 try:
@@ -35,9 +35,6 @@
     from collections import MutableMapping
     from collections import Sequence
 
-
-_CURRENT_SPAN_CV = contextvars.ContextVar('current_span', default=None)
-
 MAX_NUM_ATTRIBUTES = 32
 MAX_NUM_EVENTS = 128
 MAX_NUM_LINKS = 32
@@ -287,21 +284,20 @@ class Tracer(trace_api.Tracer):
     """See `opentelemetry.trace.Tracer`.
 
     Args:
-        cv: The context variable that holds the current span.
+        name: The name of the tracer.
     """
 
     def __init__(self,
-                 cv: 'contextvars.ContextVar' = _CURRENT_SPAN_CV
+                 name: str = ''
                  ) -> None:
-        self._cv = cv
-        try:
-            self._cv.get()
-        except LookupError:
-            self._cv.set(None)
+        slot_name = 'current_span'
+        if name:
+            slot_name = '{}.current_span'.format(name)
+        self._current_span_slot = Context.register_slot(slot_name)
 
     def get_current_span(self):
         """See `opentelemetry.trace.Tracer.get_current_span`."""
-        return self._cv.get()
+        return self._current_span_slot.get()
 
     @contextmanager
     def start_span(self,
@@ -341,11 +337,12 @@ def create_span(self,
     def use_span(self, span: 'Span') -> typing.Iterator['Span']:
         """See `opentelemetry.trace.Tracer.use_span`."""
         span.start()
-        token = self._cv.set(span)
+        span_snapshot = self._current_span_slot.get()
+        self._current_span_slot.set(span)
         try:
             yield span
         finally:
-            self._cv.reset(token)
+            self._current_span_slot.set(span_snapshot)
             span.end()
 
 

opentelemetry-sdk/tests/trace/test_trace.py

@@ -13,7 +13,6 @@
 # limitations under the License.
 
 from unittest import mock
-import contextvars
 import unittest
 
 from opentelemetry import trace as trace_api
@@ -30,8 +29,7 @@ def test_extends_api(self):
 class TestSpanCreation(unittest.TestCase):
 
     def test_start_span_implicit(self):
-        context = contextvars.ContextVar('test_start_span_implicit')
-        tracer = trace.Tracer(context)
+        tracer = trace.Tracer('test_start_span_implicit')
 
         self.assertIsNone(tracer.get_current_span())
 
@@ -69,8 +67,7 @@ def test_start_span_implicit(self):
         self.assertIsNotNone(root.end_time)
 
     def test_start_span_explicit(self):
-        context = contextvars.ContextVar('test_start_span_explicit')
-        tracer = trace.Tracer(context)
+        tracer = trace.Tracer('test_start_span_explicit')
 
         other_parent = trace_api.SpanContext(
             trace_id=0x000000000000000000000000deadbeef,