Fix witness class fail, because of different class loaders.

apm-sniffer/apm-agent-core/src/main/java/org/skywalking/apm/agent/core/plugin/AbstractClassEnhancePluginDefine.java

 package org.skywalking.apm.agent.core.plugin;
 
 import net.bytebuddy.dynamic.DynamicType;
-import net.bytebuddy.pool.TypePool;
-import net.bytebuddy.pool.TypePool.Resolution;
 import org.skywalking.apm.agent.core.plugin.interceptor.enhance.ClassEnhancePluginDefine;
 import org.skywalking.apm.util.StringUtil;
 import org.skywalking.apm.logging.ILog;
@@ -17,8 +15,6 @@ import org.skywalking.apm.logging.LogManager;
 public abstract class AbstractClassEnhancePluginDefine {
     private static final ILog logger = LogManager.getLogger(AbstractClassEnhancePluginDefine.class);
 
-    private TypePool classTypePool;
-
     /**
      * Main entrance of enhancing the class.
      *
@@ -28,7 +24,7 @@ public abstract class AbstractClassEnhancePluginDefine {
      * @throws PluginException, when set builder failure.
      */
     public DynamicType.Builder<?> define(String transformClassName,
-                                         DynamicType.Builder<?> builder) throws PluginException {
+        DynamicType.Builder<?> builder, ClassLoader classLoader) throws PluginException {
         String interceptorDefineClassName = this.getClass().getName();
 
         if (StringUtil.isEmpty(transformClassName)) {
@@ -44,8 +40,7 @@ public abstract class AbstractClassEnhancePluginDefine {
         String[] witnessClasses = witnessClasses();
         if (witnessClasses != null) {
             for (String witnessClass : witnessClasses) {
-                Resolution witnessClassResolution = classTypePool.describe(witnessClass);
-                if (!witnessClassResolution.isResolved()) {
+                if (!WitnessClassFinder.INSTANCE.exist(witnessClass, classLoader)) {
                     logger.warn("enhance class {} by plugin {} is not working. Because witness class {} is not existed.", transformClassName, interceptorDefineClassName,
                         witnessClass);
                     return null;
@@ -86,8 +81,4 @@ public abstract class AbstractClassEnhancePluginDefine {
     protected String[] witnessClasses() {
         return new String[] {};
     }
-
-    public void setClassTypePool(TypePool classTypePool) {
-        this.classTypePool = classTypePool;
-    }
 }

apm-sniffer/apm-agent-core/src/main/java/org/skywalking/apm/agent/core/plugin/PluginBootstrap.java

 package org.skywalking.apm.agent.core.plugin;
 
-import net.bytebuddy.pool.TypePool;
 import org.skywalking.apm.logging.ILog;
 import org.skywalking.apm.logging.LogManager;
 
@@ -24,8 +23,6 @@ public class PluginBootstrap {
      * @return plugin definition list.
      */
     public List<AbstractClassEnhancePluginDefine> loadPlugins() {
-        TypePool classTypePool = TypePool.Default.ofClassPath();
-
         PluginResourcesResolver resolver = new PluginResourcesResolver();
         List<URL> resources = resolver.getResources();
 
@@ -50,7 +47,6 @@ public class PluginBootstrap {
                 logger.debug("loading plugin class {}.", pluginDefine.getDefineClass());
                 AbstractClassEnhancePluginDefine plugin =
                     (AbstractClassEnhancePluginDefine) Class.forName(pluginDefine.getDefineClass()).newInstance();
-                plugin.setClassTypePool(classTypePool);
                 plugins.add(plugin);
             } catch (Throwable t) {
                 logger.error(t, "load plugin [{}] failure.", pluginDefine.getDefineClass());

apm-sniffer/apm-agent-core/src/main/java/org/skywalking/apm/agent/core/plugin/TracingBootstrap.java

@@ -62,7 +62,7 @@ public class TracingBootstrap {
             }
             DynamicType.Builder<?> newClassBuilder =
                 new ByteBuddy().rebase(resolution.resolve(), ClassFileLocator.ForClassLoader.ofClassPath());
-            newClassBuilder = ((AbstractClassEnhancePluginDefine) plugin).define(enhanceClassName, newClassBuilder);
+            newClassBuilder = ((AbstractClassEnhancePluginDefine)plugin).define(enhanceClassName, newClassBuilder, TracingBootstrap.class.getClassLoader());
             newClassBuilder.make(new TypeResolutionStrategy.Active()).load(ClassLoader.getSystemClassLoader(), ClassLoadingStrategy.Default.INJECTION)
                 .getLoaded();
         }

apm-sniffer/apm-agent-core/src/main/java/org/skywalking/apm/agent/core/plugin/WitnessClassFinder.java

+package org.skywalking.apm.agent.core.plugin;
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import net.bytebuddy.pool.TypePool;
+
+/**
+ * The <code>WitnessClassFinder</code> represents a pool of {@link TypePool}s,
+ * each {@link TypePool} matches a {@link ClassLoader},
+ * which helps to find the class define existed or not.
+ *
+ * @author wusheng
+ */
+public enum WitnessClassFinder {
+    INSTANCE;
+
+    private Map<ClassLoader, TypePool> poolMap = new ConcurrentHashMap<ClassLoader, TypePool>();
+
+    /**
+     * @param witnessClass
+     * @param classLoader for finding the witnessClass
+     * @return true, if the given witnessClass exists, through the given classLoader.
+     */
+    public boolean exist(String witnessClass, ClassLoader classLoader) {
+        ClassLoader mappingKey = classLoader == null ? NullClassLoader.INSTANCE : classLoader;
+        if (!poolMap.containsKey(witnessClass)) {
+            synchronized (poolMap) {
+                if (!poolMap.containsKey(witnessClass)) {
+                    TypePool classTypePool = classLoader == null ? TypePool.Default.ofClassPath() : TypePool.Default.of(classLoader);
+                    poolMap.put(mappingKey, classTypePool);
+                }
+            }
+        }
+        TypePool typePool = poolMap.get(mappingKey);
+        TypePool.Resolution witnessClassResolution = typePool.describe(witnessClass);
+        return witnessClassResolution.isResolved();
+    }
+}
+
+final class NullClassLoader extends ClassLoader {
+    static NullClassLoader INSTANCE = new NullClassLoader();
+}

apm-sniffer/apm-agent-core/src/test/java/org/skywalking/apm/agent/core/plugin/AbstractClassEnhancePluginDefineTest.java

@@ -104,12 +104,12 @@ public class AbstractClassEnhancePluginDefineTest {
 
         private DynamicType.Builder<?> transformStaticMethod(DynamicType.Builder newBuilder) {
             MockPluginStaticMethodInstrumentation staticMethodInstrumentation = new MockPluginStaticMethodInstrumentation();
-            return staticMethodInstrumentation.define(WEAVE_CLASS, newBuilder);
+            return staticMethodInstrumentation.define(WEAVE_CLASS, newBuilder, AbstractClassEnhancePluginDefineTest.class.getClassLoader());
         }
 
         private DynamicType.Builder transformInstanceMethod(DynamicType.Builder<?> builder) {
             MockPluginInstanceMethodInstrumentation instrumentation = new MockPluginInstanceMethodInstrumentation();
-            return instrumentation.define(WEAVE_CLASS, builder);
+            return instrumentation.define(WEAVE_CLASS, builder, AbstractClassEnhancePluginDefineTest.class.getClassLoader());
         }
     }
 

apm-sniffer/apm-agent/src/main/java/org/skywalking/apm/agent/SkyWalkingAgent.java

@@ -57,7 +57,7 @@ public class SkyWalkingAgent {
                 ClassLoader classLoader) {
                 List<AbstractClassEnhancePluginDefine> pluginDefines = pluginFinder.find(typeDescription.getTypeName());
                 for (AbstractClassEnhancePluginDefine pluginDefine : pluginDefines) {
-                    DynamicType.Builder<?> newBuilder = pluginDefine.define(typeDescription.getTypeName(), builder);
+                    DynamicType.Builder<?> newBuilder = pluginDefine.define(typeDescription.getTypeName(), builder, classLoader);
                     if (newBuilder != null) {
                         return newBuilder;
                     }