8255883: Avoid duplicated GeneratedMethodAccessor when reflect method invoked from different threads

Reviewed-by: shade, alanb

src/java.base/share/classes/jdk/internal/reflect/NativeConstructorAccessorImpl.java

@@ -28,14 +28,20 @@ package jdk.internal.reflect;
 import sun.reflect.misc.ReflectUtil;
 
 import java.lang.reflect.*;
+import jdk.internal.misc.Unsafe;
 
 /** Used only for the first few invocations of a Constructor;
     afterward, switches to bytecode-based implementation */
 
 class NativeConstructorAccessorImpl extends ConstructorAccessorImpl {
+    private static final Unsafe U = Unsafe.getUnsafe();
+    private static final long GENERATED_OFFSET
+        = U.objectFieldOffset(NativeConstructorAccessorImpl.class, "generated");
+
     private final Constructor<?> c;
     private DelegatingConstructorAccessorImpl parent;
     private int numInvocations;
+    private volatile int generated;
 
     NativeConstructorAccessorImpl(Constructor<?> c) {
         this.c = c;
@@ -51,14 +57,22 @@ class NativeConstructorAccessorImpl extends ConstructorAccessorImpl {
         // be found from the generated bytecode.
         if (++numInvocations > ReflectionFactory.inflationThreshold()
                 && !c.getDeclaringClass().isHidden()
-                && !ReflectUtil.isVMAnonymousClass(c.getDeclaringClass())) {
-            ConstructorAccessorImpl acc = (ConstructorAccessorImpl)
-                new MethodAccessorGenerator().
-                    generateConstructor(c.getDeclaringClass(),
-                                        c.getParameterTypes(),
-                                        c.getExceptionTypes(),
-                                        c.getModifiers());
-            parent.setDelegate(acc);
+                && !ReflectUtil.isVMAnonymousClass(c.getDeclaringClass())
+                && generated == 0
+                && U.compareAndSetInt(this, GENERATED_OFFSET, 0, 1)) {
+            try {
+                ConstructorAccessorImpl acc = (ConstructorAccessorImpl)
+                    new MethodAccessorGenerator().
+                        generateConstructor(c.getDeclaringClass(),
+                                            c.getParameterTypes(),
+                                            c.getExceptionTypes(),
+                                            c.getModifiers());
+                parent.setDelegate(acc);
+            } catch (Throwable t) {
+                // Throwable happens in generateConstructor, restore generated to 0
+                generated = 0;
+                throw t;
+            }
         }
 
         return newInstance0(c, args);

src/java.base/share/classes/jdk/internal/reflect/NativeMethodAccessorImpl.java

@@ -28,14 +28,20 @@ package jdk.internal.reflect;
 import sun.reflect.misc.ReflectUtil;
 
 import java.lang.reflect.*;
+import jdk.internal.misc.Unsafe;
 
 /** Used only for the first few invocations of a Method; afterward,
     switches to bytecode-based implementation */
 
 class NativeMethodAccessorImpl extends MethodAccessorImpl {
+     private static final Unsafe U = Unsafe.getUnsafe();
+     private static final long GENERATED_OFFSET
+        = U.objectFieldOffset(NativeMethodAccessorImpl.class, "generated");
+
     private final Method method;
     private DelegatingMethodAccessorImpl parent;
     private int numInvocations;
+    private volatile int generated;
 
     NativeMethodAccessorImpl(Method method) {
         this.method = method;
@@ -49,16 +55,24 @@ class NativeMethodAccessorImpl extends MethodAccessorImpl {
         // found from the generated bytecode.
         if (++numInvocations > ReflectionFactory.inflationThreshold()
                 && !method.getDeclaringClass().isHidden()
-                && !ReflectUtil.isVMAnonymousClass(method.getDeclaringClass())) {
-            MethodAccessorImpl acc = (MethodAccessorImpl)
-                new MethodAccessorGenerator().
-                    generateMethod(method.getDeclaringClass(),
-                                   method.getName(),
-                                   method.getParameterTypes(),
-                                   method.getReturnType(),
-                                   method.getExceptionTypes(),
-                                   method.getModifiers());
-            parent.setDelegate(acc);
+                && !ReflectUtil.isVMAnonymousClass(method.getDeclaringClass())
+                && generated == 0
+                && U.compareAndSetInt(this, GENERATED_OFFSET, 0, 1)) {
+            try {
+                MethodAccessorImpl acc = (MethodAccessorImpl)
+                    new MethodAccessorGenerator().
+                        generateMethod(method.getDeclaringClass(),
+                                       method.getName(),
+                                       method.getParameterTypes(),
+                                       method.getReturnType(),
+                                       method.getExceptionTypes(),
+                                       method.getModifiers());
+                parent.setDelegate(acc);
+            } catch (Throwable t) {
+                // Throwable happens in generateMethod, restore generated to 0
+                generated = 0;
+                throw t;
+            }
         }
 
         return invoke0(method, obj, args);