Prevent Netty periodic purge tasks from inheriting context

dd-java-agent/instrumentation/netty/netty-concurrent-4.0/src/main/java/datadog/trace/instrumentation/netty40/concurrent/SingleThreadEventExecutorStartThreadInstrumentation.java

@@ -0,0 +1,59 @@
+package datadog.trace.instrumentation.netty40.concurrent;
+
+import static datadog.trace.agent.tooling.bytebuddy.matcher.NameMatchers.named;
+import static datadog.trace.bootstrap.instrumentation.api.AgentTracer.isAsyncPropagationEnabled;
+import static datadog.trace.bootstrap.instrumentation.api.AgentTracer.setAsyncPropagationEnabled;
+import static net.bytebuddy.matcher.ElementMatchers.isPrivate;
+import static net.bytebuddy.matcher.ElementMatchers.returns;
+import static net.bytebuddy.matcher.ElementMatchers.takesNoArguments;
+
+import com.google.auto.service.AutoService;
+import datadog.trace.agent.tooling.Instrumenter;
+import datadog.trace.agent.tooling.InstrumenterModule;
+import net.bytebuddy.asm.Advice;
+
+/** Prevents Netty's lazily created event-loop maintenance tasks from inheriting user context. */
+@AutoService(InstrumenterModule.class)
+public final class SingleThreadEventExecutorStartThreadInstrumentation
+    extends InstrumenterModule.ContextTracking
+    implements Instrumenter.ForKnownTypes, Instrumenter.HasMethodAdvice {
+
+  public SingleThreadEventExecutorStartThreadInstrumentation() {
+    super("netty-concurrent", "netty-event-executor");
+  }
+
+  @Override
+  public String[] knownMatchingTypes() {
+    return new String[] {
+      "io.netty.util.concurrent.SingleThreadEventExecutor",
+      "io.grpc.netty.shaded.io.netty.util.concurrent.SingleThreadEventExecutor",
+      "com.couchbase.client.deps.io.netty.util.concurrent.SingleThreadEventExecutor",
+      "play.shaded.ahc.io.netty.util.concurrent.SingleThreadEventExecutor",
+    };
+  }
+
+  @Override
+  public void methodAdvice(MethodTransformer transformer) {
+    transformer.applyAdvice(
+        named("startThread").and(takesNoArguments()).and(returns(void.class)).and(isPrivate()),
+        getClass().getName() + "$DisableAsyncPropagation");
+  }
+
+  public static final class DisableAsyncPropagation {
+    @Advice.OnMethodEnter(suppress = Throwable.class)
+    public static boolean before() {
+      if (isAsyncPropagationEnabled()) {
+        setAsyncPropagationEnabled(false);
+        return true;
+      }
+      return false;
+    }
+
+    @Advice.OnMethodExit(onThrowable = Throwable.class, suppress = Throwable.class)
+    public static void after(@Advice.Enter boolean wasDisabled) {
+      if (wasDisabled) {
+        setAsyncPropagationEnabled(true);
+      }
+    }
+  }
+}