Add experimental updateTracerConfigurations for dynamically updateable on/off instrumentation

sdk/all/src/main/java/io/opentelemetry/sdk/OpenTelemetrySdk.java

@@ -19,6 +19,8 @@
 import io.opentelemetry.sdk.metrics.SdkMeterProvider;
 import io.opentelemetry.sdk.trace.SdkTracerProvider;
 import java.io.Closeable;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.TimeUnit;
@@ -168,6 +170,20 @@
     public SdkTracerProvider unobfuscate() {
       return delegate;
     }
+
+    // currently not public as experimental
+    void updateTracerConfigurations() {
+      // and delegate method is experimental so also not public
+      // It would be: delegate.updateTracerConfigurations();
+      try {
+        Method method = SdkTracerProvider.class.getDeclaredMethod("updateTracerConfigurations");
+        method.setAccessible(true);
+        method.invoke(delegate);
+      } catch (NoSuchMethodException | IllegalAccessException | InvocationTargetException e) {
+        throw new IllegalStateException(
+            "Error calling SdkTracerProvider.updateTracerConfigurations(): ", e);
+      }
+    }
   }
 
   /**

sdk/trace/src/main/java/io/opentelemetry/sdk/trace/SdkTracer.java

@@ -19,9 +19,8 @@
 
   private final TracerSharedState sharedState;
   private final InstrumentationScopeInfo instrumentationScopeInfo;
-
-  // TODO: add dedicated API for updating scope config.
-  @SuppressWarnings("FieldCanBeFinal") // For now, allow updating reflectively.
+  // deliberately not volatile because of performance concerns
+  // - which means its eventually consistent
   private boolean tracerEnabled;
 
   SdkTracer(
@@ -54,6 +53,11 @@
     return instrumentationScopeInfo;
   }
 
+  // currently not public as experimental
+  void updateTracerConfig(TracerConfig tracerConfig) {
+    this.tracerEnabled = tracerConfig.isEnabled();
+  }
+
   @Override
   public boolean isEnabled() {
     return tracerEnabled;

sdk/trace/src/main/java/io/opentelemetry/sdk/trace/SdkTracerProvider.java

@@ -100,6 +100,16 @@
     return sharedState.getSampler();
   }
 
+  // currently not public as experimental
+  void updateTracerConfigurations() {
+    this.tracerSdkComponentRegistry
+        .getComponents()
+        .forEach(
+            sdkTracer ->
+                sdkTracer.updateTracerConfig(
+                    getTracerConfig(sdkTracer.getInstrumentationScopeInfo())));
+  }
+
   /**
    * Attempts to stop all the activity for {@link Tracer}s created by this provider. Calls {@link
    * SpanProcessor#shutdown()} for all registered {@link SpanProcessor}s.