chore(tracing): make ddtrace.trace.Tracer a singleton (#12209)

This PR ensures an error is logged when more than one instance of the
Tracer is initialized in a process. In all scenarios the global tracer
must be used to trace an application.

## Checklist
- [x] PR author has checked that all the criteria below are met
- The PR description includes an overview of the change
- The PR description articulates the motivation for the change
- The change includes tests OR the PR description describes a testing
strategy
- The PR description notes risks associated with the change, if any
- Newly-added code is easy to change
- The change follows the [library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
- The change includes or references documentation updates if necessary
- Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist
- [x] Reviewer has checked that all the criteria below are met 
- Title is accurate
- All changes are related to the pull request's stated goal
- Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- Testing strategy adequately addresses listed risks
- Newly-added code is easy to change
- Release note makes sense to a user of the library
- If necessary, author has acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment
- Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

Author: mabdinur

ddtrace/_trace/tracer.py

@@ -217,16 +217,8 @@ def __init__(
             if Tracer._instance is None:
                 Tracer._instance = self
             else:
-                # ddtrace library does not support context propagation for multiple tracers.
-                # All instances of ddtrace ContextProviders share the same ContextVars. This means that
-                # if you create multiple instances of Tracer, spans will be shared between them creating a
-                # broken experience.
-                # TODO(mabdinur): Convert this warning to an ValueError in 3.0.0
-                deprecate(
-                    "Support for multiple Tracer instances is deprecated",
-                    ". Use ddtrace.tracer instead.",
-                    category=DDTraceDeprecationWarning,
-                    removal_version="3.0.0",
+                log.error(
+                    "Multiple Tracer instances can not be initialized. Use ``ddtrace.trace.tracer`` instead.",
                 )
 
         self._user_trace_processors: List[TraceProcessor] = []

releasenotes/notes/drop-multitracer-support-ec109486f71c9c62.yaml

@@ -0,0 +1,4 @@
+---
+upgrade:
+  - |
+    tracing: Drops support for multiple Tracer instances in the same process. Use ``ddtrace.trace.tracer`` to access the global tracer instance.

tests/ci_visibility/test_ci_visibility.py

@@ -28,6 +28,7 @@
 from ddtrace.internal.ci_visibility.git_client import METADATA_UPLOAD_STATUS
 from ddtrace.internal.ci_visibility.git_client import CIVisibilityGitClient
 from ddtrace.internal.ci_visibility.git_client import CIVisibilityGitClientSerializerV1
+from ddtrace.internal.ci_visibility.recorder import CIVisibilityTracer
 from ddtrace.internal.ci_visibility.recorder import _extract_repository_name_from_url
 import ddtrace.internal.test_visibility._internal_item_ids
 from ddtrace.internal.utils.http import Response
@@ -685,7 +686,7 @@ def test_civisibilitywriter_evp_proxy_url(self):
         ), mock.patch(
             "ddtrace.internal.agent.get_trace_url", return_value="http://evpproxy.bar:1234"
         ), mock.patch("ddtrace.settings._config.Config", _get_default_civisibility_ddconfig()), mock.patch(
-            "ddtrace.tracer", ddtrace.trace.Tracer()
+            "ddtrace.tracer", CIVisibilityTracer()
         ), mock.patch(
             "ddtrace.internal.ci_visibility.recorder.CIVisibility._agent_evp_proxy_is_available", return_value=True
         ), _dummy_noop_git_client(), mock.patch(
@@ -705,7 +706,7 @@ def test_civisibilitywriter_only_traces(self):
             )
         ), mock.patch(
             "ddtrace.internal.agent.get_trace_url", return_value="http://onlytraces:1234"
-        ), mock.patch("ddtrace.tracer", ddtrace.trace.Tracer()), mock.patch(
+        ), mock.patch("ddtrace.tracer", CIVisibilityTracer()), mock.patch(
             "ddtrace.internal.ci_visibility.recorder.CIVisibility._agent_evp_proxy_is_available", return_value=False
         ), mock.patch(
             "ddtrace.internal.ci_visibility.writer.config", ddtrace.settings.Config()
@@ -1119,7 +1120,7 @@ def test_civisibility_enable_respects_passed_in_tracer():
     ), _dummy_noop_git_client(), mock.patch(
         "ddtrace.internal.ci_visibility.recorder.ddconfig", _get_default_civisibility_ddconfig()
     ), mock.patch("ddtrace.internal.ci_visibility.writer.config", ddtrace.settings.Config()):
-        tracer = ddtrace.trace.Tracer()
+        tracer = CIVisibilityTracer()
         tracer._configure(partial_flush_enabled=False, partial_flush_min_spans=100)
         CIVisibility.enable(tracer=tracer)
         assert CIVisibility._instance.tracer._partial_flush_enabled is False

tests/ci_visibility/util.py

@@ -12,6 +12,7 @@
 from ddtrace.internal.ci_visibility.git_client import METADATA_UPLOAD_STATUS
 from ddtrace.internal.ci_visibility.git_client import CIVisibilityGitClient
 from ddtrace.internal.ci_visibility.recorder import CIVisibility
+from ddtrace.internal.ci_visibility.recorder import CIVisibilityTracer
 from ddtrace.internal.test_visibility._internal_item_ids import InternalTestId
 from tests.utils import DummyCIVisibilityWriter
 from tests.utils import override_env
@@ -209,5 +210,5 @@ def _ci_override_env(
     new_vars: t.Optional[t.Dict[str, str]] = None, mock_ci_env=False, replace_os_env=True, full_clear=False
 ):
     env_vars = _get_default_ci_env_vars(new_vars, mock_ci_env, full_clear)
-    with override_env(env_vars, replace_os_env=replace_os_env), mock.patch("ddtrace.tracer", ddtrace.trace.Tracer()):
+    with override_env(env_vars, replace_os_env=replace_os_env), mock.patch("ddtrace.tracer", CIVisibilityTracer()):
         yield

tests/contrib/aiomysql/test_aiomysql.py

@@ -9,7 +9,6 @@
 from ddtrace.contrib.internal.aiomysql.patch import unpatch
 from ddtrace.internal.schema import DEFAULT_SPAN_SERVICE_NAME
 from ddtrace.trace import Pin
-from ddtrace.trace import Tracer
 from tests.contrib import shared_tests_async as shared_tests
 from tests.contrib.asyncio.utils import AsyncioTestCase
 from tests.contrib.asyncio.utils import mark_asyncio
@@ -31,19 +30,16 @@ def patch_aiomysql():
 @pytest.fixture
 async def patched_conn(tracer):
     conn = await aiomysql.connect(**AIOMYSQL_CONFIG)
-    Pin.get_from(conn).clone(tracer=tracer).onto(conn)
     yield conn
     conn.close()
 
 
 @pytest.fixture()
-async def snapshot_conn():
-    tracer = Tracer()
+async def snapshot_conn(tracer):
     conn = await aiomysql.connect(**AIOMYSQL_CONFIG)
-    Pin.get_from(conn).clone(tracer=tracer).onto(conn)
     yield conn
     conn.close()
-    tracer.shutdown()
+    tracer.flush()
 
 
 @pytest.mark.asyncio

tests/contrib/flask_cache/test_utils.py

@@ -6,7 +6,7 @@
 from ddtrace.contrib.internal.flask_cache.utils import _extract_client
 from ddtrace.contrib.internal.flask_cache.utils import _extract_conn_tags
 from ddtrace.contrib.internal.flask_cache.utils import _resource_from_cache_prefix
-from ddtrace.trace import Tracer
+from ddtrace.trace import tracer
 
 from ..config import MEMCACHED_CONFIG
 from ..config import REDIS_CONFIG
@@ -17,7 +17,6 @@ class FlaskCacheUtilsTest(unittest.TestCase):
 
     def test_extract_redis_connection_metadata(self):
         # create the TracedCache instance for a Flask app
-        tracer = Tracer()
         Cache = get_traced_cache(tracer, service=self.SERVICE)
         app = Flask(__name__)
         config = {
@@ -37,7 +36,6 @@ def test_extract_redis_connection_metadata(self):
 
     def test_extract_memcached_connection_metadata(self):
         # create the TracedCache instance for a Flask app
-        tracer = Tracer()
         Cache = get_traced_cache(tracer, service=self.SERVICE)
         app = Flask(__name__)
         config = {
@@ -56,7 +54,6 @@ def test_extract_memcached_connection_metadata(self):
 
     def test_extract_memcached_multiple_connection_metadata(self):
         # create the TracedCache instance for a Flask app
-        tracer = Tracer()
         Cache = get_traced_cache(tracer, service=self.SERVICE)
         app = Flask(__name__)
         config = {
@@ -78,7 +75,6 @@ def test_extract_memcached_multiple_connection_metadata(self):
 
     def test_resource_from_cache_with_prefix(self):
         # create the TracedCache instance for a Flask app
-        tracer = Tracer()
         Cache = get_traced_cache(tracer, service=self.SERVICE)
         app = Flask(__name__)
         config = {
@@ -94,7 +90,6 @@ def test_resource_from_cache_with_prefix(self):
 
     def test_resource_from_cache_with_empty_prefix(self):
         # create the TracedCache instance for a Flask app
-        tracer = Tracer()
         Cache = get_traced_cache(tracer, service=self.SERVICE)
         app = Flask(__name__)
         config = {
@@ -110,7 +105,6 @@ def test_resource_from_cache_with_empty_prefix(self):
 
     def test_resource_from_cache_without_prefix(self):
         # create the TracedCache instance for a Flask app
-        tracer = Tracer()
         Cache = get_traced_cache(tracer, service=self.SERVICE)
         app = Flask(__name__)
         traced_cache = Cache(app, config={"CACHE_TYPE": "redis"})

tests/contrib/tornado/test_config.py

@@ -1,6 +1,5 @@
 from ddtrace.trace import TraceFilter
-from ddtrace.trace import Tracer
-from tests.utils import DummyWriter
+from tests.utils import DummyTracer
 
 from .utils import TornadoTestCase
 
@@ -19,8 +18,7 @@ class TestTornadoSettings(TornadoTestCase):
     """
 
     def get_app(self):
-        # Override with a real tracer
-        self.tracer = Tracer()
+        self.tracer = DummyTracer()
         super(TestTornadoSettings, self).get_app()
 
     def get_settings(self):
@@ -40,25 +38,6 @@ def get_settings(self):
             },
         }
 
-    def test_tracer_is_properly_configured(self):
-        # the tracer must be properly configured
-        assert self.tracer._tags.get("env") == "production"
-        assert self.tracer._tags.get("debug") == "false"
-        assert self.tracer.enabled is False
-        assert self.tracer.agent_trace_url == "http://dd-agent.service.consul:8126"
-
-        writer = DummyWriter()
-        self.tracer._configure(enabled=True, writer=writer)
-        with self.tracer.trace("keep"):
-            pass
-        spans = writer.pop()
-        assert len(spans) == 1
-
-        with self.tracer.trace("drop"):
-            pass
-        spans = writer.pop()
-        assert len(spans) == 0
-
 
 class TestTornadoSettingsEnabled(TornadoTestCase):
     def get_settings(self):

tests/integration/test_debug.py

@@ -3,8 +3,6 @@
 import os
 import re
 import subprocess
-from typing import List
-from typing import Optional
 
 import mock
 import pytest
@@ -13,11 +11,10 @@
 import ddtrace._trace.sampler
 from ddtrace.internal import debug
 from ddtrace.internal.writer import AgentWriter
-from ddtrace.internal.writer import TraceWriter
-from ddtrace.trace import Span
 from tests.integration.utils import AGENT_VERSION
 from tests.subprocesstest import SubprocessTestCase
 from tests.subprocesstest import run_in_subprocess
+from tests.utils import DummyTracer
 
 
 pytestmark = pytest.mark.skipif(AGENT_VERSION == "testagent", reason="The test agent doesn't support startup logs.")
@@ -189,13 +186,12 @@ def test_trace_agent_url(self):
         )
     )
     def test_tracer_loglevel_info_connection(self):
-        tracer = ddtrace.trace.Tracer()
         logging.basicConfig(level=logging.INFO)
         with mock.patch.object(logging.Logger, "log") as mock_logger:
             # shove an unserializable object into the config log output
             # regression: this used to cause an exception to be raised
             ddtrace.config.version = AgentWriter(agent_url="foobar")
-            tracer._configure()
+            ddtrace.trace.tracer.configure()
         assert mock.call(logging.INFO, re_matcher("- DATADOG TRACER CONFIGURATION - ")) in mock_logger.mock_calls
 
     @run_in_subprocess(
@@ -205,10 +201,9 @@ def test_tracer_loglevel_info_connection(self):
         )
     )
     def test_tracer_loglevel_info_no_connection(self):
-        tracer = ddtrace.trace.Tracer()
         logging.basicConfig(level=logging.INFO)
         with mock.patch.object(logging.Logger, "log") as mock_logger:
-            tracer._configure()
+            ddtrace.trace.tracer.configure()
         assert mock.call(logging.INFO, re_matcher("- DATADOG TRACER CONFIGURATION - ")) in mock_logger.mock_calls
         assert mock.call(logging.WARNING, re_matcher("- DATADOG TRACER DIAGNOSTIC - ")) in mock_logger.mock_calls
 
@@ -219,9 +214,8 @@ def test_tracer_loglevel_info_no_connection(self):
         )
     )
     def test_tracer_log_disabled_error(self):
-        tracer = ddtrace.trace.Tracer()
         with mock.patch.object(logging.Logger, "log") as mock_logger:
-            tracer._configure()
+            ddtrace.trace.tracer._configure()
         assert mock_logger.mock_calls == []
 
     @run_in_subprocess(
@@ -231,9 +225,8 @@ def test_tracer_log_disabled_error(self):
         )
     )
     def test_tracer_log_disabled(self):
-        tracer = ddtrace.trace.Tracer()
         with mock.patch.object(logging.Logger, "log") as mock_logger:
-            tracer._configure()
+            ddtrace.trace.tracer._configure()
         assert mock_logger.mock_calls == []
 
     @run_in_subprocess(
@@ -243,9 +236,8 @@ def test_tracer_log_disabled(self):
     )
     def test_tracer_info_level_log(self):
         logging.basicConfig(level=logging.INFO)
-        tracer = ddtrace.trace.Tracer()
         with mock.patch.object(logging.Logger, "log") as mock_logger:
-            tracer._configure()
+            ddtrace.trace.tracer._configure()
         assert mock_logger.mock_calls == []
 
 
@@ -287,16 +279,24 @@ def test_to_json():
     json.dumps(info)
 
 
+@pytest.mark.subprocess(env={"AWS_LAMBDA_FUNCTION_NAME": "something"})
 def test_agentless(monkeypatch):
-    monkeypatch.setenv("AWS_LAMBDA_FUNCTION_NAME", "something")
-    tracer = ddtrace.trace.Tracer()
-    info = debug.collect(tracer)
+    from ddtrace.internal import debug
+    from ddtrace.trace import tracer
 
+    info = debug.collect(tracer)
     assert info.get("agent_url") == "AGENTLESS"
 
 
+@pytest.mark.subprocess()
 def test_custom_writer():
-    tracer = ddtrace.trace.Tracer()
+    from typing import List
+    from typing import Optional
+
+    from ddtrace.internal import debug
+    from ddtrace.internal.writer import TraceWriter
+    from ddtrace.trace import Span
+    from ddtrace.trace import tracer
 
     class CustomWriter(TraceWriter):
         def recreate(self) -> TraceWriter:
@@ -317,16 +317,24 @@ def flush_queue(self) -> None:
     assert info.get("agent_url") == "CUSTOM"
 
 
+@pytest.mark.subprocess()
 def test_different_samplers():
-    tracer = ddtrace.trace.Tracer()
+    import ddtrace
+    from ddtrace.internal import debug
+    from ddtrace.trace import tracer
+
     tracer._configure(sampler=ddtrace._trace.sampler.RateSampler())
     info = debug.collect(tracer)
 
     assert info.get("sampler_type") == "RateSampler"
 
 
+@pytest.mark.subprocess()
 def test_startup_logs_sampling_rules():
-    tracer = ddtrace.trace.Tracer()
+    import ddtrace
+    from ddtrace.internal import debug
+    from ddtrace.trace import tracer
+
     sampler = ddtrace._trace.sampler.DatadogSampler(rules=[ddtrace._trace.sampler.SamplingRule(sample_rate=1.0)])
     tracer._configure(sampler=sampler)
     f = debug.collect(tracer)
@@ -415,7 +423,7 @@ def test_debug_span_log():
 
 
 def test_partial_flush_log():
-    tracer = ddtrace.trace.Tracer()
+    tracer = DummyTracer()
 
     tracer._configure(
         partial_flush_enabled=True,

tests/integration/test_encoding.py

@@ -4,15 +4,14 @@
 import mock
 import pytest
 
-from ddtrace.trace import Tracer
+from ddtrace.trace import tracer
 
 
 AGENT_VERSION = os.environ.get("AGENT_VERSION")
 
 
 class TestTraceAcceptedByAgent:
     def test_simple_trace_accepted_by_agent(self):
-        tracer = Tracer()
         with mock.patch("ddtrace.internal.writer.writer.log") as log:
             with tracer.trace("root"):
                 for _ in range(999):
@@ -32,7 +31,6 @@ def test_simple_trace_accepted_by_agent(self):
     )
     def test_trace_with_meta_accepted_by_agent(self, tags):
         """Meta tags should be text types."""
-        tracer = Tracer()
         with mock.patch("ddtrace.internal.writer.writer.log") as log:
             with tracer.trace("root", service="test_encoding", resource="test_resource") as root:
                 root.set_tags(tags)
@@ -53,7 +51,6 @@ def test_trace_with_meta_accepted_by_agent(self, tags):
     )
     def test_trace_with_metrics_accepted_by_agent(self, metrics):
         """Metric tags should be numeric types - i.e. int, float, long (py3), and str numbers."""
-        tracer = Tracer()
         with mock.patch("ddtrace.internal.writer.writer.log") as log:
             with tracer.trace("root") as root:
                 root.set_metrics(metrics)
@@ -72,7 +69,6 @@ def test_trace_with_metrics_accepted_by_agent(self, metrics):
     )
     def test_trace_with_links_accepted_by_agent(self, span_links_kwargs):
         """Links should not break things."""
-        tracer = Tracer()
         with mock.patch("ddtrace.internal.writer.writer.log") as log:
             with tracer.trace("root", service="test_encoding", resource="test_resource") as root:
                 root.set_link(**span_links_kwargs)