Lazily load and execute service discovery

Author: amarziali

dd-java-agent/agent-tooling/src/main/java/datadog/trace/agent/tooling/TracerInstaller.java

@@ -52,16 +52,22 @@ private static void maybeEnableServiceDiscovery(CoreTracerBuilder tracerBuilder)
       log.debug("service discovery not supported on native images");
       return;
     }
-    try {
-      // use reflection to load MemFDUnixWriter so it doesn't get picked up when we transitively
-      // look for all tracer class dependencies to install in GraalVM via VMRuntimeInstrumentation
-      Class<?> memFdClass =
-          Class.forName("datadog.trace.agent.tooling.servicediscovery.MemFDUnixWriter");
-      ForeignMemoryWriter memFd = (ForeignMemoryWriter) memFdClass.getConstructor().newInstance();
-      tracerBuilder.serviceDiscovery(new ServiceDiscovery(memFd));
-    } catch (Throwable e) {
-      log.debug("service discovery not supported", e);
-    }
+    tracerBuilder.serviceDiscoveryFactory(
+        () -> {
+          try {
+            // use reflection to load MemFDUnixWriter so it doesn't get picked up when we
+            // transitively look for all tracer class dependencies to install in GraalVM via
+            // VMRuntimeInstrumentation
+            Class<?> memFdClass =
+                Class.forName("datadog.trace.agent.tooling.servicediscovery.MemFDUnixWriter");
+            ForeignMemoryWriter memFd =
+                (ForeignMemoryWriter) memFdClass.getConstructor().newInstance();
+            return new ServiceDiscovery(memFd);
+          } catch (Throwable e) {
+            log.debug("service discovery not supported", e);
+            return null;
+          }
+        });
   }
 
   public static void installGlobalTracer(final CoreTracer tracer) {

dd-trace-core/src/main/java/datadog/trace/core/CoreTracer.java

@@ -97,6 +97,7 @@
 import datadog.trace.core.propagation.XRayPropagator;
 import datadog.trace.core.scopemanager.ContinuableScopeManager;
 import datadog.trace.core.servicediscovery.ServiceDiscovery;
+import datadog.trace.core.servicediscovery.ServiceDiscoveryFactory;
 import datadog.trace.core.taginterceptor.RuleFlags;
 import datadog.trace.core.taginterceptor.TagInterceptor;
 import datadog.trace.core.traceinterceptor.LatencyTraceInterceptor;
@@ -322,7 +323,7 @@ public static class CoreTracerBuilder {
     private TagInterceptor tagInterceptor;
     private boolean strictTraceWrites;
     private InstrumentationGateway instrumentationGateway;
-    private ServiceDiscovery serviceDiscovery;
+    private ServiceDiscoveryFactory serviceDiscoveryFactory;
     private TimeSource timeSource;
     private DataStreamsMonitoring dataStreamsMonitoring;
     private ProfilingContextIntegration profilingContextIntegration =
@@ -438,8 +439,9 @@ public CoreTracerBuilder instrumentationGateway(InstrumentationGateway instrumen
       return this;
     }
 
-    public CoreTracerBuilder serviceDiscovery(ServiceDiscovery serviceDiscovery) {
-      this.serviceDiscovery = serviceDiscovery;
+    public CoreTracerBuilder serviceDiscoveryFactory(
+        ServiceDiscoveryFactory serviceDiscoveryFactory) {
+      this.serviceDiscoveryFactory = serviceDiscoveryFactory;
       return this;
     }
 
@@ -535,7 +537,7 @@ public CoreTracer build() {
           tagInterceptor,
           strictTraceWrites,
           instrumentationGateway,
-          serviceDiscovery,
+          serviceDiscoveryFactory,
           timeSource,
           dataStreamsMonitoring,
           profilingContextIntegration,
@@ -628,7 +630,7 @@ private CoreTracer(
       final TagInterceptor tagInterceptor,
       final boolean strictTraceWrites,
       final InstrumentationGateway instrumentationGateway,
-      final ServiceDiscovery serviceDiscovery,
+      final ServiceDiscoveryFactory serviceDiscoveryFactory,
       final TimeSource timeSource,
       final DataStreamsMonitoring dataStreamsMonitoring,
       final ProfilingContextIntegration profilingContextIntegration,
@@ -897,8 +899,18 @@ private CoreTracer(
 
     this.localRootSpanTagsNeedIntercept =
         this.tagInterceptor.needsIntercept(this.localRootSpanTags);
-    if (serviceDiscovery != null) {
-      serviceDiscovery.writeTracerMetadata(config);
+    if (serviceDiscoveryFactory != null) {
+      AgentTaskScheduler.get()
+          .schedule(
+              () -> {
+                final ServiceDiscovery serviceDiscovery =
+                    serviceDiscoveryFactory.createServiceDiscovery();
+                if (serviceDiscovery != null) {
+                  serviceDiscovery.writeTracerMetadata(config);
+                }
+              },
+              1,
+              SECONDS);
     }
   }
 

dd-trace-core/src/main/java/datadog/trace/core/servicediscovery/ServiceDiscoveryFactory.java

@@ -0,0 +1,6 @@
+package datadog.trace.core.servicediscovery;
+
+@FunctionalInterface
+public interface ServiceDiscoveryFactory {
+  ServiceDiscovery createServiceDiscovery();
+}