Improve lockObject string calculation

Author: Dmytro Ukhlov

core/src/main/java/hudson/util/DelegatingClassLoader.java

@@ -75,7 +75,7 @@ protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundE
      * <p>Fails fast if a subclass erroneously defines a class here, which would violate the
      * delegation-only contract and could reintroduce locking/retention issues.
      */
-    protected Class<?> verify(Class<?> clazz) {
+    private Class<?> verify(Class<?> clazz) {
         if (clazz.getClassLoader() == this) {
             throw new IllegalStateException("DelegatingClassLoader must not be the defining loader: " + clazz.getName());
         }

core/src/main/java/hudson/util/ExistenceCheckingClassLoader.java

@@ -48,13 +48,13 @@ public ExistenceCheckingClassLoader(ClassLoader parent) {
     protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
         // Add support for loading of JaCoCo dynamic instrumentation classes
         if (name.equals("java.lang.$JaCoCo")) {
-            return verify(super.loadClass(name, resolve));
+            return super.loadClass(name, resolve);
         }
 
         if (getResource(name.replace('.', '/') + ".class") == null) {
             throw new ClassNotFoundException(name);
         }
 
-        return verify(super.loadClass(name, resolve));
+        return super.loadClass(name, resolve);
     }
 }

core/src/main/java/jenkins/util/URLClassLoader2.java

@@ -3,6 +3,7 @@
 import java.net.URL;
 import java.net.URLClassLoader;
 import java.util.Objects;
+import java.util.concurrent.atomic.AtomicInteger;
 import jenkins.ClassLoaderReflectionToolkit;
 import org.kohsuke.accmod.Restricted;
 import org.kohsuke.accmod.restrictions.NoExternalUse;
@@ -13,6 +14,10 @@
  */
 @Restricted(NoExternalUse.class)
 public class URLClassLoader2 extends URLClassLoader implements JenkinsClassLoader {
+    private static final AtomicInteger NEXT_INSTANCE_NUMBER = new AtomicInteger(0);
+
+    private final String lockObjectPrefixName = String.format("%s@%x-loadClassLock:",
+            URLClassLoader2.class.getName(), NEXT_INSTANCE_NUMBER.getAndIncrement());
 
     static {
         registerAsParallelCapable();
@@ -85,13 +90,6 @@ public Class<?> findLoadedClass2(String name) {
     @Override
     public Object getClassLoadingLock(String className) {
         Objects.requireNonNull(className);
-        return new StringBuilder(128)
-                .append(getClass().getSimpleName())
-                .append("@")
-                .append(Integer.toHexString(System.identityHashCode(this)))
-                .append("-loadClassLock:")
-                .append(className)
-                .toString()
-                .intern();
+        return (lockObjectPrefixName + className).intern();
     }
 }