From 75137db51acc2acccffbda6ca6671a2a5c4ac1f2 Mon Sep 17 00:00:00 2001
From: Douglas Barker <doug.barker@gmail.com>
Date: Thu, 7 May 2026 15:04:16 -0400
Subject: [PATCH 1/7] [SDK] Support dynamic TracerConfigurator updates

---
 examples/CMakeLists.txt                       |   1 +
 examples/tracer_configurator/CMakeLists.txt   |  12 ++
 examples/tracer_configurator/main.cc          | 146 +++++++++++++++
 sdk/include/opentelemetry/sdk/trace/tracer.h  |  14 +-
 .../opentelemetry/sdk/trace/tracer_context.h  |   9 +
 .../opentelemetry/sdk/trace/tracer_provider.h |  10 +
 sdk/src/trace/tracer.cc                       |  21 ++-
 sdk/src/trace/tracer_context.cc               |   7 +
 sdk/src/trace/tracer_provider.cc              |  20 ++
 sdk/test/trace/BUILD                          |   1 +
 sdk/test/trace/tracer_provider_test.cc        | 175 ++++++++++++++++++
 11 files changed, 412 insertions(+), 4 deletions(-)
 create mode 100644 examples/tracer_configurator/CMakeLists.txt
 create mode 100644 examples/tracer_configurator/main.cc

diff --git a/examples/CMakeLists.txt b/examples/CMakeLists.txt
index 3ce9d6859b..21171f12cd 100644
--- a/examples/CMakeLists.txt
+++ b/examples/CMakeLists.txt
@@ -28,6 +28,7 @@ add_subdirectory(metrics_simple)
 add_subdirectory(multithreaded)
 add_subdirectory(multi_processor)
 add_subdirectory(environment_carrier)
+add_subdirectory(tracer_configurator)
 
 if(WITH_EXAMPLES_HTTP)
   add_subdirectory(http)
diff --git a/examples/tracer_configurator/CMakeLists.txt b/examples/tracer_configurator/CMakeLists.txt
new file mode 100644
index 0000000000..831fea9a08
--- /dev/null
+++ b/examples/tracer_configurator/CMakeLists.txt
@@ -0,0 +1,12 @@
+# Copyright The OpenTelemetry Authors
+# SPDX-License-Identifier: Apache-2.0
+
+add_executable(example_tracer_configurator main.cc)
+target_link_libraries(
+  example_tracer_configurator PRIVATE opentelemetry-cpp::trace
+                                      opentelemetry-cpp::ostream_span_exporter)
+
+if(BUILD_TESTING)
+  add_test(NAME examples.tracer_configurator
+           COMMAND "$<TARGET_FILE:example_tracer_configurator>")
+endif()
diff --git a/examples/tracer_configurator/main.cc b/examples/tracer_configurator/main.cc
new file mode 100644
index 0000000000..11982c0427
--- /dev/null
+++ b/examples/tracer_configurator/main.cc
@@ -0,0 +1,146 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+// This example shows how to use TracerProvider::UpdateTracerConfigurator to control which
+// tracers are enabled at runtime. Updating the TracerConfigurator affects all existing and future
+// tracers provided by the TracerProvider. It is thread safe and can be called concurrently with
+// tracer and span creation.
+//
+// Two instrumentation scopes are shown:
+// 1. "my_library" (example instrumented user code),
+// 2. "external_library_foo" (example instrumented third-party dependency).
+//
+// The example simulates a debugging workflow where only the tracer configuration is changed at
+// runtime through the provider:
+//
+//   Stage 1 – Start with all tracing disabled (low-overhead production default).
+//   Stage 2 – An issue is reported. Enable only the user library traces to get an initial signal.
+//   Stage 3 – The issue involves external libraries too. Enable all traces for full visibility.
+//   Stage 4 – Investigation complete. Disable all tracing again.
+
+#include <initializer_list>
+#include <iostream>
+#include <memory>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "opentelemetry/exporters/ostream/span_exporter_factory.h"
+#include "opentelemetry/nostd/string_view.h"
+#include "opentelemetry/sdk/instrumentationscope/scope_configurator.h"
+#include "opentelemetry/sdk/resource/resource.h"
+#include "opentelemetry/sdk/trace/random_id_generator.h"
+#include "opentelemetry/sdk/trace/samplers/always_on.h"
+#include "opentelemetry/sdk/trace/simple_processor_factory.h"
+#include "opentelemetry/sdk/trace/tracer_config.h"
+#include "opentelemetry/sdk/trace/tracer_provider.h"
+#include "opentelemetry/version.h"
+
+namespace trace_sdk      = opentelemetry::sdk::trace;
+namespace trace_exporter = opentelemetry::exporter::trace;
+namespace scope_cfg      = opentelemetry::sdk::instrumentationscope;
+namespace nostd          = opentelemetry::nostd;
+
+namespace
+{
+void DoWork(opentelemetry::nostd::shared_ptr<opentelemetry::trace::Tracer> &tracer,
+            nostd::string_view tracer_name,
+            nostd::string_view operation)
+{
+  auto span = tracer->StartSpan(operation);
+  std::cout << (span->IsRecording() ? "[active] " : "[off]    ") << tracer_name << " / "
+            << operation << "\n";
+  span->End();
+}
+
+// Builds a ScopeConfigurator that enables all tracers (the default).
+std::unique_ptr<scope_cfg::ScopeConfigurator<trace_sdk::TracerConfig>> EnableAll()
+{
+  return std::make_unique<scope_cfg::ScopeConfigurator<trace_sdk::TracerConfig>>(
+      scope_cfg::ScopeConfigurator<trace_sdk::TracerConfig>::Builder(
+          trace_sdk::TracerConfig::Default())
+          .Build());
+}
+
+// Builds a ScopeConfigurator that enables only the named tracers; all others are disabled.
+std::unique_ptr<scope_cfg::ScopeConfigurator<trace_sdk::TracerConfig>> EnableOnly(
+    std::initializer_list<nostd::string_view> names)
+{
+  scope_cfg::ScopeConfigurator<trace_sdk::TracerConfig>::Builder builder(
+      trace_sdk::TracerConfig::Disabled());
+  for (nostd::string_view name : names)
+  {
+    builder.AddConditionNameEquals(name, trace_sdk::TracerConfig::Default());
+  }
+  return std::make_unique<scope_cfg::ScopeConfigurator<trace_sdk::TracerConfig>>(builder.Build());
+}
+
+// Builds a ScopeConfigurator that disables all tracers.
+std::unique_ptr<scope_cfg::ScopeConfigurator<trace_sdk::TracerConfig>> DisableAll()
+{
+  return std::make_unique<scope_cfg::ScopeConfigurator<trace_sdk::TracerConfig>>(
+      scope_cfg::ScopeConfigurator<trace_sdk::TracerConfig>::Builder(
+          trace_sdk::TracerConfig::Disabled())
+          .Build());
+}
+}  // namespace
+
+int main()
+{
+  auto exporter  = trace_exporter::OStreamSpanExporterFactory::Create();
+  auto processor = trace_sdk::SimpleSpanProcessorFactory::Create(std::move(exporter));
+
+  // Start with all tracing disabled
+  auto provider = std::make_shared<trace_sdk::TracerProvider>(
+      std::move(processor), opentelemetry::sdk::resource::Resource::Create({}),
+      std::make_unique<trace_sdk::AlwaysOnSampler>(),
+      std::make_unique<trace_sdk::RandomIdGenerator>(), DisableAll());
+
+  auto my_library_tracer           = provider->GetTracer("my_library");
+  auto external_library_foo_tracer = provider->GetTracer("external_library_foo");
+
+  // -------------------------------------------------------------------------
+  // Stage 1: all tracing disabled
+  // -------------------------------------------------------------------------
+  std::cout << "=== Stage 1: disable all (production default) ===\n";
+
+  DoWork(my_library_tracer, "my_library", "DoWork");                            // disabled
+  DoWork(external_library_foo_tracer, "external_library_foo", "FooOperation");  // disabled
+
+  // -------------------------------------------------------------------------
+  // Stage 2: enable only user library tracing
+  //
+  // EnableOnly() sets Disabled() as the default and adds explicit per-name
+  // overrides. Existing tracer handles reflect the change immediately
+  // -------------------------------------------------------------------------
+  std::cout << "\n=== Stage 2: enable only 'my_library' ===\n";
+
+  provider->UpdateTracerConfigurator(EnableOnly({"my_library"}));
+
+  DoWork(my_library_tracer, "my_library", "DoWork");                            // enabled
+  DoWork(external_library_foo_tracer, "external_library_foo", "FooOperation");  // disabled
+
+  // -------------------------------------------------------------------------
+  // Stage 3: enable tracing in all libraries
+  // -------------------------------------------------------------------------
+  std::cout << "\n=== Stage 3: enable all ===\n";
+
+  provider->UpdateTracerConfigurator(EnableAll());
+
+  DoWork(my_library_tracer, "my_library", "DoWork");                            // enabled
+  DoWork(external_library_foo_tracer, "external_library_foo", "FooOperation");  // enabled
+
+  // -------------------------------------------------------------------------
+  // Stage 4: disable all tracing again
+  // -------------------------------------------------------------------------
+  std::cout << "\n=== Stage 4: disable all ===\n";
+
+  provider->UpdateTracerConfigurator(DisableAll());
+
+  DoWork(my_library_tracer, "my_library", "DoWork");                            // disabled
+  DoWork(external_library_foo_tracer, "external_library_foo", "FooOperation");  // disabled
+
+  provider->ForceFlush();
+  provider->Shutdown();
+  return 0;
+}
diff --git a/sdk/include/opentelemetry/sdk/trace/tracer.h b/sdk/include/opentelemetry/sdk/trace/tracer.h
index 26693e1896..02c794b12f 100644
--- a/sdk/include/opentelemetry/sdk/trace/tracer.h
+++ b/sdk/include/opentelemetry/sdk/trace/tracer.h
@@ -8,6 +8,7 @@
 #include "opentelemetry/common/key_value_iterable.h"
 #include "opentelemetry/nostd/shared_ptr.h"
 #include "opentelemetry/nostd/string_view.h"
+#include "opentelemetry/sdk/common/atomic_shared_ptr.h"
 #include "opentelemetry/sdk/instrumentationscope/instrumentation_scope.h"
 #include "opentelemetry/sdk/resource/resource.h"
 #include "opentelemetry/sdk/trace/id_generator.h"
@@ -103,11 +104,22 @@ class Tracer final : public opentelemetry::trace::Tracer,
   Sampler &GetSampler() { return context_->GetSampler(); }
 
 private:
+  // TracerProvider needs access to UpdateTracerConfig to propagate configuration updates to
+  // existing tracers.
+  friend class TracerProvider;
+
+  /**
+   * Update this tracer's TracerConfig. Called only by
+   * TracerProvider::UpdateTracerConfigurator when the provider-level
+   * TracerConfigurator is replaced at runtime.
+   */
+  void UpdateTracerConfig(const TracerConfig &config) noexcept;
+
   // order of declaration is important here - instrumentation scope should destroy after
   // tracer-context.
   std::shared_ptr<InstrumentationScope> instrumentation_scope_;
   std::shared_ptr<TracerContext> context_;
-  TracerConfig tracer_config_;
+  opentelemetry::sdk::common::AtomicSharedPtr<const TracerConfig> tracer_config_;
   static const std::shared_ptr<opentelemetry::trace::NoopTracer> kNoopTracer;
 };
 }  // namespace trace
diff --git a/sdk/include/opentelemetry/sdk/trace/tracer_context.h b/sdk/include/opentelemetry/sdk/trace/tracer_context.h
index 81edbb5322..518c1cbdf6 100644
--- a/sdk/include/opentelemetry/sdk/trace/tracer_context.h
+++ b/sdk/include/opentelemetry/sdk/trace/tracer_context.h
@@ -102,6 +102,15 @@ class TracerContext
    */
   opentelemetry::sdk::trace::IdGenerator &GetIdGenerator() const noexcept;
 
+  /**
+   * Replace the TracerConfigurator for this context.
+   *
+   * Note: This method is not thread safe.
+   * @param tracer_configurator The new configurator.
+   */
+  void SetTracerConfigurator(std::unique_ptr<instrumentationscope::ScopeConfigurator<TracerConfig>>
+                                 tracer_configurator) noexcept;
+
   /**
    * Force all active SpanProcessors to flush any buffered spans
    * within the given timeout.
diff --git a/sdk/include/opentelemetry/sdk/trace/tracer_provider.h b/sdk/include/opentelemetry/sdk/trace/tracer_provider.h
index 096f64bec6..6e4be011df 100644
--- a/sdk/include/opentelemetry/sdk/trace/tracer_provider.h
+++ b/sdk/include/opentelemetry/sdk/trace/tracer_provider.h
@@ -109,6 +109,16 @@ class OPENTELEMETRY_EXPORT TracerProvider final : public opentelemetry::trace::T
    */
   void AddProcessor(std::unique_ptr<SpanProcessor> processor) noexcept;
 
+  /**
+   * Update the TracerConfigurator for this provider, recreate and propagate the resulting
+   * TracerConfig to all existing Tracers while new Tracers will use the updated configuration.
+   *
+   * @param tracer_configurator The new configurator.
+   */
+  void UpdateTracerConfigurator(
+      std::unique_ptr<instrumentationscope::ScopeConfigurator<TracerConfig>>
+          tracer_configurator) noexcept;
+
   /**
    * Obtain the resource associated with this tracer provider.
    * @return The resource for this tracer provider.
diff --git a/sdk/src/trace/tracer.cc b/sdk/src/trace/tracer.cc
index b3d5477318..a99c606e0b 100644
--- a/sdk/src/trace/tracer.cc
+++ b/sdk/src/trace/tracer.cc
@@ -45,10 +45,11 @@ Tracer::Tracer(std::shared_ptr<TracerContext> context,
                std::unique_ptr<InstrumentationScope> instrumentation_scope) noexcept
     : instrumentation_scope_{std::move(instrumentation_scope)},
       context_{std::move(context)},
-      tracer_config_(context_->GetTracerConfigurator().ComputeConfig(*instrumentation_scope_))
+      tracer_config_(std::make_shared<const TracerConfig>(
+          context_->GetTracerConfigurator().ComputeConfig(*instrumentation_scope_)))
 {
 #if OPENTELEMETRY_ABI_VERSION_NO >= 2
-  UpdateEnabled(tracer_config_.IsEnabled());
+  UpdateEnabled(tracer_config_.load()->IsEnabled());
 #endif
 }
 
@@ -58,7 +59,12 @@ nostd::shared_ptr<opentelemetry::trace::Span> Tracer::StartSpan(
     const opentelemetry::trace::SpanContextKeyValueIterable &links,
     const opentelemetry::trace::StartSpanOptions &options) noexcept
 {
-  if (!tracer_config_.IsEnabled())
+  // Check if the tracer is enabled using the API Tracer::Enabled() accessor if available.
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+  if (!Enabled())
+#else
+  if (!tracer_config_.load()->IsEnabled())
+#endif
   {
     return kNoopTracer->StartSpan(name, attributes, links, options);
   }
@@ -199,6 +205,15 @@ void Tracer::CloseWithMicroseconds(uint64_t timeout) noexcept
         std::chrono::microseconds{static_cast<std::chrono::microseconds::rep>(timeout)});
   }
 }
+
+void Tracer::UpdateTracerConfig(const TracerConfig &config) noexcept
+{
+  tracer_config_.store(std::make_shared<const TracerConfig>(config));
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+  UpdateEnabled(config.IsEnabled());
+#endif
+}
+
 }  // namespace trace
 }  // namespace sdk
 OPENTELEMETRY_END_NAMESPACE
diff --git a/sdk/src/trace/tracer_context.cc b/sdk/src/trace/tracer_context.cc
index c3cbfb9d76..9f87b96c87 100644
--- a/sdk/src/trace/tracer_context.cc
+++ b/sdk/src/trace/tracer_context.cc
@@ -64,6 +64,13 @@ void TracerContext::AddProcessor(std::unique_ptr<SpanProcessor> processor) noexc
   multi_processor->AddProcessor(std::move(processor));
 }
 
+void TracerContext::SetTracerConfigurator(
+    std::unique_ptr<instrumentationscope::ScopeConfigurator<TracerConfig>>
+        tracer_configurator) noexcept
+{
+  tracer_configurator_ = std::move(tracer_configurator);
+}
+
 SpanProcessor &TracerContext::GetProcessor() const noexcept
 {
   return *processor_;
diff --git a/sdk/src/trace/tracer_provider.cc b/sdk/src/trace/tracer_provider.cc
index e6837985c2..90b6a7c92e 100644
--- a/sdk/src/trace/tracer_provider.cc
+++ b/sdk/src/trace/tracer_provider.cc
@@ -129,6 +129,26 @@ void TracerProvider::AddProcessor(std::unique_ptr<SpanProcessor> processor) noex
   context_->AddProcessor(std::move(processor));
 }
 
+void TracerProvider::UpdateTracerConfigurator(
+    std::unique_ptr<instrumentationscope::ScopeConfigurator<TracerConfig>>
+        tracer_configurator) noexcept
+{
+  // The only way to set the TracerConfig of a tracer is on Tracer construction in
+  // TracerProvider::GetTracer or through Tracer::UpdateTracerConfig (which is private and only
+  // accessed by TracerProvider).
+  //
+  // Lock the provider mutex while updating the TracerConfiguartor in the context and setting the
+  // new TracerConfig of all existing tracers.
+  const std::lock_guard<std::mutex> guard(lock_);
+  context_->SetTracerConfigurator(std::move(tracer_configurator));
+  for (auto &tracer : tracers_)
+  {
+    auto new_config =
+        context_->GetTracerConfigurator().ComputeConfig(tracer->GetInstrumentationScope());
+    tracer->UpdateTracerConfig(new_config);
+  }
+}
+
 const resource::Resource &TracerProvider::GetResource() const noexcept
 {
   return context_->GetResource();
diff --git a/sdk/test/trace/BUILD b/sdk/test/trace/BUILD
index 06ca595858..2de6d3c733 100644
--- a/sdk/test/trace/BUILD
+++ b/sdk/test/trace/BUILD
@@ -14,6 +14,7 @@ cc_test(
         "trace",
     ],
     deps = [
+        "//exporters/memory:in_memory_span_exporter",
         "//sdk/src/resource",
         "//sdk/src/trace",
         "@com_google_googletest//:gtest_main",
diff --git a/sdk/test/trace/tracer_provider_test.cc b/sdk/test/trace/tracer_provider_test.cc
index a3434afdd1..a63ea92cf7 100644
--- a/sdk/test/trace/tracer_provider_test.cc
+++ b/sdk/test/trace/tracer_provider_test.cc
@@ -6,10 +6,16 @@
 #include <utility>
 #include <vector>
 
+#include <atomic>
+#include <future>
+#include <thread>
+
 #include "opentelemetry/common/macros.h"
+#include "opentelemetry/exporters/memory/in_memory_span_exporter.h"
 #include "opentelemetry/nostd/shared_ptr.h"
 #include "opentelemetry/nostd/string_view.h"
 #include "opentelemetry/sdk/instrumentationscope/instrumentation_scope.h"
+#include "opentelemetry/sdk/instrumentationscope/scope_configurator.h"
 #include "opentelemetry/sdk/resource/resource.h"
 #include "opentelemetry/sdk/trace/exporter.h"
 #include "opentelemetry/sdk/trace/id_generator.h"
@@ -17,9 +23,11 @@
 #include "opentelemetry/sdk/trace/random_id_generator.h"
 #include "opentelemetry/sdk/trace/sampler.h"
 #include "opentelemetry/sdk/trace/samplers/always_off.h"
+#include "opentelemetry/sdk/trace/samplers/always_on.h"
 #include "opentelemetry/sdk/trace/simple_processor.h"
 #include "opentelemetry/sdk/trace/simple_processor_factory.h"
 #include "opentelemetry/sdk/trace/tracer.h"
+#include "opentelemetry/sdk/trace/tracer_config.h"
 #include "opentelemetry/sdk/trace/tracer_context.h"
 #include "opentelemetry/sdk/trace/tracer_provider.h"
 #include "opentelemetry/sdk/trace/tracer_provider_factory.h"
@@ -37,6 +45,7 @@
 
 using namespace opentelemetry::sdk::trace;
 using namespace opentelemetry::sdk::resource;
+using opentelemetry::sdk::instrumentationscope::ScopeConfigurator;
 
 TEST(TracerProvider, GetTracer)
 {
@@ -341,3 +350,169 @@ TEST(TracerProvider, ForceFlush)
 
   EXPECT_TRUE(tp1.ForceFlush());
 }
+
+TEST(TracerProvider, UpdateTracerConfiguratorDisableByName)
+{
+  auto processor = SimpleSpanProcessorFactory::Create(
+      std::make_unique<opentelemetry::exporter::memory::InMemorySpanExporter>());
+
+  // Start with all tracers enabled (the default configurator enables everything).
+  TracerProvider provider(std::move(processor));
+
+  auto tracer_disabled_by_update = provider.GetTracer("scope.disabled");
+  auto tracer_unaffected         = provider.GetTracer("scope.unaffected");
+
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+  ASSERT_TRUE(tracer_disabled_by_update->Enabled());
+  ASSERT_TRUE(tracer_unaffected->Enabled());
+#endif
+  ASSERT_TRUE(tracer_disabled_by_update->StartSpan("op")->IsRecording());
+  ASSERT_TRUE(tracer_unaffected->StartSpan("op")->IsRecording());
+
+  // Disable "scope.disabled" by name; "scope.unaffected" must remain enabled.
+  auto configurator_with_one_scope_disabled = std::make_unique<ScopeConfigurator<TracerConfig>>(
+      ScopeConfigurator<TracerConfig>::Builder(TracerConfig::Default())
+          .AddConditionNameEquals("scope.disabled", TracerConfig::Disabled())
+          .Build());
+
+  provider.UpdateTracerConfigurator(std::move(configurator_with_one_scope_disabled));
+
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+  EXPECT_FALSE(tracer_disabled_by_update->Enabled());
+  EXPECT_TRUE(tracer_unaffected->Enabled());
+#endif
+  EXPECT_FALSE(tracer_disabled_by_update->StartSpan("op")->IsRecording());
+  EXPECT_TRUE(tracer_unaffected->StartSpan("op")->IsRecording());
+}
+
+TEST(TracerProvider, UpdateTracerConfiguratorReEnable)
+{
+  auto processor = SimpleSpanProcessorFactory::Create(
+      std::make_unique<opentelemetry::exporter::memory::InMemorySpanExporter>());
+
+  // Start with all tracers disabled via the initial configurator.
+  auto all_disabled_configurator = std::make_unique<ScopeConfigurator<TracerConfig>>(
+      ScopeConfigurator<TracerConfig>::Builder(TracerConfig::Disabled()).Build());
+  TracerProvider provider(
+      std::move(processor), Resource::Create({}), std::make_unique<AlwaysOnSampler>(),
+      std::make_unique<RandomIdGenerator>(), std::move(all_disabled_configurator));
+
+  auto existing_tracer = provider.GetTracer("scope.existing");
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+  ASSERT_FALSE(existing_tracer->Enabled());
+#endif
+  ASSERT_FALSE(existing_tracer->StartSpan("op")->IsRecording());
+
+  // Re-enable all tracers by installing a default (all-enabled) configurator.
+  auto all_enabled_configurator = std::make_unique<ScopeConfigurator<TracerConfig>>(
+      ScopeConfigurator<TracerConfig>::Builder(TracerConfig::Default()).Build());
+  provider.UpdateTracerConfigurator(std::move(all_enabled_configurator));
+
+  // The existing tracer handle must immediately reflect the updated config.
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+  EXPECT_TRUE(existing_tracer->Enabled());
+#endif
+  EXPECT_TRUE(existing_tracer->StartSpan("op")->IsRecording());
+
+  // Tracers obtained after the update also reflect the new configurator.
+  auto tracer_obtained_after_update = provider.GetTracer("scope.new");
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+  EXPECT_TRUE(tracer_obtained_after_update->Enabled());
+#endif
+  EXPECT_TRUE(tracer_obtained_after_update->StartSpan("op")->IsRecording());
+}
+
+TEST(TracerProvider, UpdateTracerConfiguratorNewTracerUsesUpdatedConfig)
+{
+  auto processor = SimpleSpanProcessorFactory::Create(
+      std::make_unique<opentelemetry::exporter::memory::InMemorySpanExporter>());
+  TracerProvider provider(std::move(processor));
+
+  // Install a configurator that disables "scope.disabled" before any tracer
+  // for that scope has been obtained.
+  auto configurator_with_one_scope_disabled = std::make_unique<ScopeConfigurator<TracerConfig>>(
+      ScopeConfigurator<TracerConfig>::Builder(TracerConfig::Default())
+          .AddConditionNameEquals("scope.disabled", TracerConfig::Disabled())
+          .Build());
+  provider.UpdateTracerConfigurator(std::move(configurator_with_one_scope_disabled));
+
+  // A tracer obtained after the update must already reflect the new config.
+  auto tracer_for_disabled_scope = provider.GetTracer("scope.disabled");
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+  EXPECT_FALSE(tracer_for_disabled_scope->Enabled());
+#endif
+  EXPECT_FALSE(tracer_for_disabled_scope->StartSpan("op")->IsRecording());
+
+  // Scopes not named in the disable by name configurator remain enabled.
+  auto tracer_for_unaffected_scope = provider.GetTracer("scope.unaffected");
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+  EXPECT_TRUE(tracer_for_unaffected_scope->Enabled());
+#endif
+  EXPECT_TRUE(tracer_for_unaffected_scope->StartSpan("op")->IsRecording());
+}
+
+TEST(TracerProvider, UpdateTracerConfiguratorConcurrentStartSpan)
+{
+  auto processor = SimpleSpanProcessorFactory::Create(
+      std::make_unique<opentelemetry::exporter::memory::InMemorySpanExporter>());
+  TracerProvider provider(std::move(processor));
+
+  auto tracer = provider.GetTracer("scope.concurrent");
+
+  std::atomic<bool> stop{false};
+  std::atomic<bool> worker_saw_disabled{false};
+  std::atomic<bool> worker_saw_enabled{false};
+
+  std::promise<void> worker_ready;
+  std::future<void> worker_ready_future = worker_ready.get_future();
+
+  // Worker: call StartSpan in a tight loop and flag each observed state.
+  std::thread worker([&] {
+    worker_ready.set_value();
+    while (!stop.load(std::memory_order_relaxed))
+    {
+      auto span = tracer->StartSpan("op");
+      if (span->IsRecording())
+      {
+        worker_saw_enabled.store(true, std::memory_order_relaxed);
+      }
+      else
+      {
+        worker_saw_disabled.store(true, std::memory_order_relaxed);
+      }
+      span->End();
+    }
+  });
+
+  worker_ready_future.wait();
+
+  // Disable all, then wait for the worker to actually observe a disabled span.
+  // This synchronisation guarantees the worker ran while the tracer was disabled.
+  auto disable_all = std::make_unique<ScopeConfigurator<TracerConfig>>(
+      ScopeConfigurator<TracerConfig>::Builder(TracerConfig::Disabled()).Build());
+  provider.UpdateTracerConfigurator(std::move(disable_all));
+  while (!worker_saw_disabled.load(std::memory_order_relaxed))
+  {
+    std::this_thread::yield();
+  }
+
+  // Re-enable all, then wait for the worker to observe an enabled span.
+  auto enable_all = std::make_unique<ScopeConfigurator<TracerConfig>>(
+      ScopeConfigurator<TracerConfig>::Builder(TracerConfig::Default()).Build());
+  provider.UpdateTracerConfigurator(std::move(enable_all));
+  while (!worker_saw_enabled.load(std::memory_order_relaxed))
+  {
+    std::this_thread::yield();
+  }
+
+  stop.store(true, std::memory_order_relaxed);
+  worker.join();
+
+  EXPECT_TRUE(worker_saw_disabled.load());
+  EXPECT_TRUE(worker_saw_enabled.load());
+
+  EXPECT_TRUE(tracer->StartSpan("op")->IsRecording());
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+  EXPECT_TRUE(tracer->Enabled());
+#endif
+}

From 6ee3f6902b316cc89c6f5f94193f4cb4d1e99b91 Mon Sep 17 00:00:00 2001
From: Douglas Barker <doug.barker@gmail.com>
Date: Tue, 12 May 2026 22:39:26 -0400
Subject: [PATCH 2/7] address review feedback

---
 sdk/include/opentelemetry/sdk/trace/tracer.h | 4 ++++
 sdk/src/trace/tracer.cc                      | 9 ++++++++-
 sdk/src/trace/tracer_context.cc              | 7 +++++++
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/sdk/include/opentelemetry/sdk/trace/tracer.h b/sdk/include/opentelemetry/sdk/trace/tracer.h
index 02c794b12f..b3d4bc5ace 100644
--- a/sdk/include/opentelemetry/sdk/trace/tracer.h
+++ b/sdk/include/opentelemetry/sdk/trace/tracer.h
@@ -5,6 +5,7 @@
 
 #include <stdint.h>
 
+#include <atomic>
 #include "opentelemetry/common/key_value_iterable.h"
 #include "opentelemetry/nostd/shared_ptr.h"
 #include "opentelemetry/nostd/string_view.h"
@@ -120,6 +121,9 @@ class Tracer final : public opentelemetry::trace::Tracer,
   std::shared_ptr<InstrumentationScope> instrumentation_scope_;
   std::shared_ptr<TracerContext> context_;
   opentelemetry::sdk::common::AtomicSharedPtr<const TracerConfig> tracer_config_;
+#if OPENTELEMETRY_ABI_VERSION_NO < 2
+  std::atomic<bool> is_enabled_;
+#endif
   static const std::shared_ptr<opentelemetry::trace::NoopTracer> kNoopTracer;
 };
 }  // namespace trace
diff --git a/sdk/src/trace/tracer.cc b/sdk/src/trace/tracer.cc
index a99c606e0b..d173e34f8b 100644
--- a/sdk/src/trace/tracer.cc
+++ b/sdk/src/trace/tracer.cc
@@ -47,6 +47,10 @@ Tracer::Tracer(std::shared_ptr<TracerContext> context,
       context_{std::move(context)},
       tracer_config_(std::make_shared<const TracerConfig>(
           context_->GetTracerConfigurator().ComputeConfig(*instrumentation_scope_)))
+#if OPENTELEMETRY_ABI_VERSION_NO < 2
+      ,
+      is_enabled_(tracer_config_.load()->IsEnabled())
+#endif
 {
 #if OPENTELEMETRY_ABI_VERSION_NO >= 2
   UpdateEnabled(tracer_config_.load()->IsEnabled());
@@ -63,7 +67,7 @@ nostd::shared_ptr<opentelemetry::trace::Span> Tracer::StartSpan(
 #if OPENTELEMETRY_ABI_VERSION_NO >= 2
   if (!Enabled())
 #else
-  if (!tracer_config_.load()->IsEnabled())
+  if (!is_enabled_.load(std::memory_order_relaxed))
 #endif
   {
     return kNoopTracer->StartSpan(name, attributes, links, options);
@@ -209,8 +213,11 @@ void Tracer::CloseWithMicroseconds(uint64_t timeout) noexcept
 void Tracer::UpdateTracerConfig(const TracerConfig &config) noexcept
 {
   tracer_config_.store(std::make_shared<const TracerConfig>(config));
+
 #if OPENTELEMETRY_ABI_VERSION_NO >= 2
   UpdateEnabled(config.IsEnabled());
+#else
+  is_enabled_.store(config.IsEnabled(), std::memory_order_relaxed);
 #endif
 }
 
diff --git a/sdk/src/trace/tracer_context.cc b/sdk/src/trace/tracer_context.cc
index 9f87b96c87..adb3cfe538 100644
--- a/sdk/src/trace/tracer_context.cc
+++ b/sdk/src/trace/tracer_context.cc
@@ -6,6 +6,7 @@
 #include <utility>
 #include <vector>
 
+#include "opentelemetry/sdk/common/global_log_handler.h"
 #include "opentelemetry/sdk/instrumentationscope/scope_configurator.h"
 #include "opentelemetry/sdk/resource/resource.h"
 #include "opentelemetry/sdk/trace/id_generator.h"
@@ -68,6 +69,12 @@ void TracerContext::SetTracerConfigurator(
     std::unique_ptr<instrumentationscope::ScopeConfigurator<TracerConfig>>
         tracer_configurator) noexcept
 {
+  if (!tracer_configurator)
+  {
+    OTEL_INTERNAL_LOG_ERROR(
+        "[TracerContext::SetTracerConfigurator] tracer_configurator must not be null, ignoring.");
+    return;
+  }
   tracer_configurator_ = std::move(tracer_configurator);
 }
 

From 5e79961526d9c995e6a2f5f891a292415b7ee06a Mon Sep 17 00:00:00 2001
From: Douglas Barker <doug.barker@gmail.com>
Date: Tue, 12 May 2026 22:45:49 -0400
Subject: [PATCH 3/7] add changelog entry

---
 CHANGELOG.md | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6f5dd627e9..6915aa0aeb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,9 @@ Increment the:
 
 ## [Unreleased]
 
+* [SDK] Add `TracerProvider::UpdateTracerConfigurator()` and example
+  [#4065](https://github.com/open-telemetry/opentelemetry-cpp/issues/4065)
+
 * [API] Fix `Logger::Enabled()`
   [#2667](https://github.com/open-telemetry/opentelemetry-cpp/issues/2667)
 

From ca61658d376fb9c3db90bfecff0817400ddf96cc Mon Sep 17 00:00:00 2001
From: Douglas Barker <doug.barker@gmail.com>
Date: Tue, 26 May 2026 22:41:50 -0400
Subject: [PATCH 4/7] address review feedback to reduce tracer provider lock
 scope. use mutex and value for tracer config objects

---
 sdk/include/opentelemetry/sdk/trace/tracer.h |  7 ++++---
 sdk/src/trace/tracer.cc                      | 20 ++++++++++++--------
 sdk/src/trace/tracer_provider.cc             | 20 ++++++++++++--------
 3 files changed, 28 insertions(+), 19 deletions(-)

diff --git a/sdk/include/opentelemetry/sdk/trace/tracer.h b/sdk/include/opentelemetry/sdk/trace/tracer.h
index b3d4bc5ace..eca85cd904 100644
--- a/sdk/include/opentelemetry/sdk/trace/tracer.h
+++ b/sdk/include/opentelemetry/sdk/trace/tracer.h
@@ -6,10 +6,10 @@
 #include <stdint.h>
 
 #include <atomic>
+#include <mutex>
 #include "opentelemetry/common/key_value_iterable.h"
 #include "opentelemetry/nostd/shared_ptr.h"
 #include "opentelemetry/nostd/string_view.h"
-#include "opentelemetry/sdk/common/atomic_shared_ptr.h"
 #include "opentelemetry/sdk/instrumentationscope/instrumentation_scope.h"
 #include "opentelemetry/sdk/resource/resource.h"
 #include "opentelemetry/sdk/trace/id_generator.h"
@@ -114,13 +114,14 @@ class Tracer final : public opentelemetry::trace::Tracer,
    * TracerProvider::UpdateTracerConfigurator when the provider-level
    * TracerConfigurator is replaced at runtime.
    */
-  void UpdateTracerConfig(const TracerConfig &config) noexcept;
+  void UpdateTracerConfig(TracerConfig config) noexcept;
 
   // order of declaration is important here - instrumentation scope should destroy after
   // tracer-context.
   std::shared_ptr<InstrumentationScope> instrumentation_scope_;
   std::shared_ptr<TracerContext> context_;
-  opentelemetry::sdk::common::AtomicSharedPtr<const TracerConfig> tracer_config_;
+  mutable std::mutex tracer_config_mutex_;
+  TracerConfig tracer_config_;
 #if OPENTELEMETRY_ABI_VERSION_NO < 2
   std::atomic<bool> is_enabled_;
 #endif
diff --git a/sdk/src/trace/tracer.cc b/sdk/src/trace/tracer.cc
index 0482d25a3f..df37d19c30 100644
--- a/sdk/src/trace/tracer.cc
+++ b/sdk/src/trace/tracer.cc
@@ -4,6 +4,7 @@
 #include <stdint.h>
 #include <chrono>
 #include <map>
+#include <mutex>
 #include <new>
 #include <utility>
 
@@ -43,15 +44,14 @@ Tracer::Tracer(std::shared_ptr<TracerContext> context,
                std::unique_ptr<InstrumentationScope> instrumentation_scope) noexcept
     : instrumentation_scope_{std::move(instrumentation_scope)},
       context_{std::move(context)},
-      tracer_config_(std::make_shared<const TracerConfig>(
-          context_->GetTracerConfigurator().ComputeConfig(*instrumentation_scope_)))
+      tracer_config_(context_->GetTracerConfigurator().ComputeConfig(*instrumentation_scope_))
 #if OPENTELEMETRY_ABI_VERSION_NO < 2
       ,
-      is_enabled_(tracer_config_.load()->IsEnabled())
+      is_enabled_(tracer_config_.IsEnabled())
 #endif
 {
 #if OPENTELEMETRY_ABI_VERSION_NO >= 2
-  UpdateEnabled(tracer_config_.load()->IsEnabled());
+  UpdateEnabled(tracer_config_.IsEnabled());
 #endif
 }
 
@@ -208,14 +208,18 @@ void Tracer::CloseWithMicroseconds(uint64_t timeout) noexcept
   }
 }
 
-void Tracer::UpdateTracerConfig(const TracerConfig &config) noexcept
+void Tracer::UpdateTracerConfig(TracerConfig config) noexcept
 {
-  tracer_config_.store(std::make_shared<const TracerConfig>(config));
+  const bool enabled = config.IsEnabled();
+  {
+    std::lock_guard<std::mutex> lock(tracer_config_mutex_);
+    tracer_config_ = std::move(config);
+  }
 
 #if OPENTELEMETRY_ABI_VERSION_NO >= 2
-  UpdateEnabled(config.IsEnabled());
+  UpdateEnabled(enabled);
 #else
-  is_enabled_.store(config.IsEnabled(), std::memory_order_relaxed);
+  is_enabled_.store(enabled, std::memory_order_relaxed);
 #endif
 }
 
diff --git a/sdk/src/trace/tracer_provider.cc b/sdk/src/trace/tracer_provider.cc
index ebd666925d..3086d5e0d5 100644
--- a/sdk/src/trace/tracer_provider.cc
+++ b/sdk/src/trace/tracer_provider.cc
@@ -132,19 +132,23 @@ void TracerProvider::UpdateTracerConfigurator(
     std::unique_ptr<instrumentationscope::ScopeConfigurator<TracerConfig>>
         tracer_configurator) noexcept
 {
+  // Lock the provider mutex while updating the TracerConfiguartor in the context and capture the
+  // current tracers
+  std::vector<std::shared_ptr<Tracer>> current_tracers;
+  {
+    const std::lock_guard<std::mutex> guard(lock_);
+    context_->SetTracerConfigurator(std::move(tracer_configurator));
+    current_tracers = tracers_;
+  }
+
   // The only way to set the TracerConfig of a tracer is on Tracer construction in
   // TracerProvider::GetTracer or through Tracer::UpdateTracerConfig (which is private and only
   // accessed by TracerProvider).
-  //
-  // Lock the provider mutex while updating the TracerConfiguartor in the context and setting the
-  // new TracerConfig of all existing tracers.
-  const std::lock_guard<std::mutex> guard(lock_);
-  context_->SetTracerConfigurator(std::move(tracer_configurator));
-  for (auto &tracer : tracers_)
+  for (auto &tracer : current_tracers)
   {
-    auto new_config =
+    TracerConfig new_config =
         context_->GetTracerConfigurator().ComputeConfig(tracer->GetInstrumentationScope());
-    tracer->UpdateTracerConfig(new_config);
+    tracer->UpdateTracerConfig(std::move(new_config));
   }
 }
 

From 219efc622242a4fed7aba058e5fd400ebc233807 Mon Sep 17 00:00:00 2001
From: Douglas Barker <doug.barker@gmail.com>
Date: Tue, 26 May 2026 23:20:20 -0400
Subject: [PATCH 5/7] fix iwyu and clang-tidy warnings

---
 examples/tracer_configurator/main.cc   | 7 +++++--
 sdk/src/trace/tracer.cc                | 2 +-
 sdk/src/trace/tracer_provider.cc       | 2 +-
 sdk/test/trace/tracer_provider_test.cc | 1 +
 4 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/examples/tracer_configurator/main.cc b/examples/tracer_configurator/main.cc
index 11982c0427..859fefad81 100644
--- a/examples/tracer_configurator/main.cc
+++ b/examples/tracer_configurator/main.cc
@@ -20,21 +20,24 @@
 
 #include <initializer_list>
 #include <iostream>
-#include <memory>
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "opentelemetry/exporters/ostream/span_exporter_factory.h"
+#include "opentelemetry/nostd/shared_ptr.h"
 #include "opentelemetry/nostd/string_view.h"
 #include "opentelemetry/sdk/instrumentationscope/scope_configurator.h"
 #include "opentelemetry/sdk/resource/resource.h"
+#include "opentelemetry/sdk/trace/exporter.h"
+#include "opentelemetry/sdk/trace/processor.h"
 #include "opentelemetry/sdk/trace/random_id_generator.h"
 #include "opentelemetry/sdk/trace/samplers/always_on.h"
 #include "opentelemetry/sdk/trace/simple_processor_factory.h"
 #include "opentelemetry/sdk/trace/tracer_config.h"
 #include "opentelemetry/sdk/trace/tracer_provider.h"
-#include "opentelemetry/version.h"
+#include "opentelemetry/trace/span.h"
+#include "opentelemetry/trace/tracer.h"
 
 namespace trace_sdk      = opentelemetry::sdk::trace;
 namespace trace_exporter = opentelemetry::exporter::trace;
diff --git a/sdk/src/trace/tracer.cc b/sdk/src/trace/tracer.cc
index df37d19c30..bea2397c10 100644
--- a/sdk/src/trace/tracer.cc
+++ b/sdk/src/trace/tracer.cc
@@ -213,7 +213,7 @@ void Tracer::UpdateTracerConfig(TracerConfig config) noexcept
   const bool enabled = config.IsEnabled();
   {
     std::lock_guard<std::mutex> lock(tracer_config_mutex_);
-    tracer_config_ = std::move(config);
+    tracer_config_ = config;
   }
 
 #if OPENTELEMETRY_ABI_VERSION_NO >= 2
diff --git a/sdk/src/trace/tracer_provider.cc b/sdk/src/trace/tracer_provider.cc
index 3086d5e0d5..dead7bb99d 100644
--- a/sdk/src/trace/tracer_provider.cc
+++ b/sdk/src/trace/tracer_provider.cc
@@ -148,7 +148,7 @@ void TracerProvider::UpdateTracerConfigurator(
   {
     TracerConfig new_config =
         context_->GetTracerConfigurator().ComputeConfig(tracer->GetInstrumentationScope());
-    tracer->UpdateTracerConfig(std::move(new_config));
+    tracer->UpdateTracerConfig(new_config);
   }
 }
 
diff --git a/sdk/test/trace/tracer_provider_test.cc b/sdk/test/trace/tracer_provider_test.cc
index e95257ea51..687f63d07f 100644
--- a/sdk/test/trace/tracer_provider_test.cc
+++ b/sdk/test/trace/tracer_provider_test.cc
@@ -31,6 +31,7 @@
 #include "opentelemetry/sdk/trace/tracer_context.h"
 #include "opentelemetry/sdk/trace/tracer_provider.h"
 #include "opentelemetry/sdk/trace/tracer_provider_factory.h"
+#include "opentelemetry/trace/span.h"
 #include "opentelemetry/trace/tracer.h"
 
 #if OPENTELEMETRY_ABI_VERSION_NO >= 2

From b22d0b24ea2e4263e1445b987d77bb4fa039322e Mon Sep 17 00:00:00 2001
From: Douglas Barker <doug.barker@gmail.com>
Date: Wed, 27 May 2026 21:07:46 +0000
Subject: [PATCH 6/7] fix iwyu warning

---
 sdk/src/trace/tracer.cc | 1 +
 1 file changed, 1 insertion(+)

diff --git a/sdk/src/trace/tracer.cc b/sdk/src/trace/tracer.cc
index bea2397c10..da69315d77 100644
--- a/sdk/src/trace/tracer.cc
+++ b/sdk/src/trace/tracer.cc
@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0
 
 #include <stdint.h>
+#include <atomic>
 #include <chrono>
 #include <map>
 #include <mutex>

From 9b3d78b579292fe281f8e0de5e93987824f39220 Mon Sep 17 00:00:00 2001
From: Douglas Barker <doug.barker@gmail.com>
Date: Thu, 28 May 2026 19:37:46 +0000
Subject: [PATCH 7/7] fix iwyu warning

---
 sdk/src/trace/tracer.cc | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/sdk/src/trace/tracer.cc b/sdk/src/trace/tracer.cc
index da69315d77..a7636b037c 100644
--- a/sdk/src/trace/tracer.cc
+++ b/sdk/src/trace/tracer.cc
@@ -2,7 +2,9 @@
 // SPDX-License-Identifier: Apache-2.0
 
 #include <stdint.h>
-#include <atomic>
+#if OPENTELEMETRY_ABI_VERSION_NO < 2
+#  include <atomic>
+#endif
 #include <chrono>
 #include <map>
 #include <mutex>