Prototype proxy tracer/provider to enable lazy setup of tracing pipeline

.github/workflows/test.yml

@@ -10,7 +10,7 @@ env:
   # Otherwise, set variable to the commit of your branch on
   # opentelemetry-python-contrib which is compatible with these Core repo
   # changes.
-  CONTRIB_REPO_SHA: fbd7e07d0b3f9be37ddfdbc8b12b35f0a8d71ede
+  CONTRIB_REPO_SHA: 1064da4bf2afaa0fb84fa10f573b211efeba72bc
 
 jobs:
   build:

CHANGELOG.md

@@ -21,6 +21,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#1722](https://github.com/open-telemetry/opentelemetry-python/pull/1722))
 - Fix B3 propagator to never return None.
   ([#1750](https://github.com/open-telemetry/opentelemetry-python/pull/1750))
+- Added ProxyTracerProvider and ProxyTracer implementations to allow fetching provider
+  and tracer instances before a global provider is set up.
+  ([#1726](https://github.com/open-telemetry/opentelemetry-python/pull/1726))
 
 
 ## [1.0.0](https://github.com/open-telemetry/opentelemetry-python/releases/tag/v1.0.0) - 2021-03-26

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

@@ -74,6 +74,7 @@
 """
 
 
+import os
 from abc import ABC, abstractmethod
 from contextlib import contextmanager
 from enum import Enum
@@ -220,6 +221,21 @@ def get_tracer(
         return _DefaultTracer()
 
 
+class ProxyTracerProvider(TracerProvider):
+    def get_tracer(
+        self,
+        instrumenting_module_name: str,
+        instrumenting_library_version: str = "",
+    ) -> "Tracer":
+        if _TRACER_PROVIDER:
+            return _TRACER_PROVIDER.get_tracer(
+                instrumenting_module_name, instrumenting_library_version
+            )
+        return ProxyTracer(
+            instrumenting_module_name, instrumenting_library_version
+        )
+
+
 class Tracer(ABC):
     """Handles span creation and in-process context propagation.
 
@@ -349,6 +365,40 @@ def start_as_current_span(
         """
 
 
+class ProxyTracer(Tracer):
+    # pylint: disable=W0222,signature-differs
+    def __init__(
+        self,
+        instrumenting_module_name: str,
+        instrumenting_library_version: str,
+    ):
+        self._instrumenting_module_name = instrumenting_module_name
+        self._instrumenting_library_version = instrumenting_library_version
+        self._real_tracer: Optional[Tracer] = None
+        self._noop_tracer = _DefaultTracer()
+
+    @property
+    def _tracer(self) -> Tracer:
+        if self._real_tracer:
+            return self._real_tracer
+
+        if _TRACER_PROVIDER:
+            self._real_tracer = _TRACER_PROVIDER.get_tracer(
+                self._instrumenting_module_name,
+                self._instrumenting_library_version,
+            )
+            return self._real_tracer
+        return self._noop_tracer
+
+    def start_span(self, *args, **kwargs) -> Span:  # type: ignore
+        return self._tracer.start_span(*args, **kwargs)  # type: ignore
+
+    def start_as_current_span(  # type: ignore
+        self, *args, **kwargs
+    ) -> Span:
+        return self._tracer.start_as_current_span(*args, **kwargs)  # type: ignore
+
+
 class _DefaultTracer(Tracer):
     """The default Tracer, used when no Tracer implementation is available.
 
@@ -387,6 +437,7 @@ def start_as_current_span(
 
 
 _TRACER_PROVIDER = None
+_PROXY_TRACER_PROVIDER = None
 
 
 def get_tracer(
@@ -425,9 +476,18 @@ def set_tracer_provider(tracer_provider: TracerProvider) -> None:
 
 def get_tracer_provider() -> TracerProvider:
     """Gets the current global :class:`~.TracerProvider` object."""
-    global _TRACER_PROVIDER  # pylint: disable=global-statement
+    # pylint: disable=global-statement
+    global _TRACER_PROVIDER
+    global _PROXY_TRACER_PROVIDER
 
     if _TRACER_PROVIDER is None:
+        # if a global tracer provider has not been set either via code or env
+        # vars, return a proxy tracer provider
+        if OTEL_PYTHON_TRACER_PROVIDER not in os.environ:
+            if not _PROXY_TRACER_PROVIDER:
+                _PROXY_TRACER_PROVIDER = ProxyTracerProvider()
+            return _PROXY_TRACER_PROVIDER
+
         _TRACER_PROVIDER = cast(  # type: ignore
             "TracerProvider",
             _load_provider(OTEL_PYTHON_TRACER_PROVIDER, "tracer_provider"),

opentelemetry-api/tests/trace/test_proxy.py

@@ -0,0 +1,72 @@
+# Copyright The OpenTelemetry Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# pylint: disable=W0212,W0222,W0221
+
+import unittest
+
+from opentelemetry import trace
+from opentelemetry.trace.span import INVALID_SPAN_CONTEXT, NonRecordingSpan
+
+
+class TestProvider(trace._DefaultTracerProvider):
+    def get_tracer(
+        self, instrumentation_module_name, instrumentaiton_library_version=None
+    ):
+        return TestTracer()
+
+
+class TestTracer(trace._DefaultTracer):
+    def start_span(self, *args, **kwargs):
+        return TestSpan(INVALID_SPAN_CONTEXT)
+
+
+class TestSpan(NonRecordingSpan):
+    pass
+
+
+class TestProxy(unittest.TestCase):
+    def test_proxy_tracer(self):
+        original_provider = trace._TRACER_PROVIDER
+
+        provider = trace.get_tracer_provider()
+        # proxy provider
+        self.assertIsInstance(provider, trace.ProxyTracerProvider)
+
+        # provider returns proxy tracer
+        tracer = provider.get_tracer("proxy-test")
+        self.assertIsInstance(tracer, trace.ProxyTracer)
+
+        with tracer.start_span("span1") as span:
+            self.assertIsInstance(span, trace.NonRecordingSpan)
+
+        with tracer.start_as_current_span("span2") as span:
+            self.assertIsInstance(span, trace.NonRecordingSpan)
+
+        # set a real provider
+        trace.set_tracer_provider(TestProvider())
+
+        # tracer provider now returns real instance
+        self.assertIsInstance(trace.get_tracer_provider(), TestProvider)
+
+        # references to the old provider still work but return real tracer now
+        real_tracer = provider.get_tracer("proxy-test")
+        self.assertIsInstance(real_tracer, TestTracer)
+
+        # reference to old proxy tracer now delegates to a real tracer and
+        # creates real spans
+        with tracer.start_span("") as span:
+            self.assertIsInstance(span, TestSpan)
+
+        trace._TRACER_PROVIDER = original_provider