Improve compatibility with other agents

javaagent-tooling/src/main/java/io/opentelemetry/javaagent/tooling/AgentInstaller.java

@@ -138,6 +138,7 @@ private static void installBytebuddyAgent(
             .with(AgentBuilder.DescriptionStrategy.Default.POOL_ONLY)
             .with(AgentTooling.poolStrategy())
             .with(new ClassLoadListener())
+            .with(AgentTooling.transformListener())
             .with(AgentTooling.locationStrategy());
     if (JavaModule.isSupported()) {
       agentBuilder = agentBuilder.with(new ExposeAgentBootstrapListener(inst));

muzzle/src/main/java/io/opentelemetry/javaagent/tooling/muzzle/AgentCachingPoolStrategy.java

@@ -275,6 +275,15 @@ public TypePool.Resolution find(String className) {
       if (OBJECT_NAME.equals(className)) {
         return OBJECT_RESOLUTION;
       }
+      // Skip cache for the type that is currently being transformed.
+      // If class has been transformed by another agent or by class loader it is possible that the
+      // cached TypeDescription isn't the same as the one built from the actual bytes that are
+      // being defined. For example if another agent adds an interface to the class then returning
+      // the cached description that does not have that interface would result in bytebuddy removing
+      // that interface.
+      if (AgentTooling.isTransforming(loaderRef != null ? loaderRef.get() : null, className)) {
+        return null;
+      }
 
       TypePool.Resolution existingResolution =
           sharedResolutionCache.get(new TypeCacheKey(loaderHash, loaderRef, className));

muzzle/src/main/java/io/opentelemetry/javaagent/tooling/muzzle/AgentTooling.java

@@ -8,6 +8,7 @@
 import java.util.Iterator;
 import java.util.ServiceLoader;
 import net.bytebuddy.agent.builder.AgentBuilder;
+import net.bytebuddy.utility.JavaModule;
 
 /**
  * This class contains class references for objects shared by the agent installer as well as muzzle
@@ -22,6 +23,8 @@ public final class AgentTooling {
   private static final AgentBuilder.PoolStrategy POOL_STRATEGY =
       new AgentCachingPoolStrategy(LOCATION_STRATEGY);
 
+  private static final ThreadLocal<CurrentTransform> CURRENT_TRANSFORM = new ThreadLocal<>();
+
   public static AgentLocationStrategy locationStrategy() {
     return LOCATION_STRATEGY;
   }
@@ -30,6 +33,10 @@ public static AgentBuilder.PoolStrategy poolStrategy() {
     return POOL_STRATEGY;
   }
 
+  public static AgentBuilder.Listener transformListener() {
+    return new ClassTransformListener();
+  }
+
   private static ClassLoader getBootstrapProxy() {
     Iterator<BootstrapProxyProvider> iterator =
         ServiceLoader.load(BootstrapProxyProvider.class, AgentTooling.class.getClassLoader())
@@ -42,5 +49,38 @@ private static ClassLoader getBootstrapProxy() {
     return null;
   }
 
+  public static boolean isTransforming(ClassLoader classLoader, String className) {
+    CurrentTransform currentTransform = CURRENT_TRANSFORM.get();
+    if (currentTransform == null) {
+      return false;
+    }
+    return currentTransform.className.equals(className)
+        && currentTransform.classLoader == classLoader;
+  }
+
+  private static class ClassTransformListener extends AgentBuilder.Listener.Adapter {
+    @Override
+    public void onDiscovery(
+        String typeName, ClassLoader classLoader, JavaModule module, boolean loaded) {
+      CURRENT_TRANSFORM.set(new CurrentTransform(classLoader, typeName));
+    }
+
+    @Override
+    public void onComplete(
+        String typeName, ClassLoader classLoader, JavaModule module, boolean loaded) {
+      CURRENT_TRANSFORM.remove();
+    }
+  }
+
+  private static class CurrentTransform {
+    private final ClassLoader classLoader;
+    private final String className;
+
+    CurrentTransform(ClassLoader classLoader, String className) {
+      this.classLoader = classLoader;
+      this.className = className;
+    }
+  }
+
   private AgentTooling() {}
 }