8242451: ensure semantics of non-capturing lambdas are preserved independent of execution mode

Reviewed-by: mchung

Author: gilles-duboscq

src/java.base/share/classes/java/lang/invoke/InnerClassLambdaMetafactory.java

@@ -57,6 +57,7 @@
     private static final String METHOD_DESCRIPTOR_VOID = Type.getMethodDescriptor(Type.VOID_TYPE);
     private static final String JAVA_LANG_OBJECT = "java/lang/Object";
     private static final String NAME_CTOR = "<init>";
+    private static final String LAMBDA_INSTANCE_FIELD = "LAMBDA_INSTANCE$";
 
     //Serialization support
     private static final String NAME_SERIALIZED_LAMBDA = "java/lang/invoke/SerializedLambda";
@@ -206,32 +207,42 @@ private static String lambdaClassName(Class<?> targetClass) {
     @Override
     CallSite buildCallSite() throws LambdaConversionException {
         final Class<?> innerClass = spinInnerClass();
-        if (invokedType.parameterCount() == 0 && !disableEagerInitialization) {
+        if (invokedType.parameterCount() == 0) {
             // In the case of a non-capturing lambda, we optimize linkage by pre-computing a single instance,
             // unless we've suppressed eager initialization
-            final Constructor<?>[] ctrs = AccessController.doPrivileged(
-                    new PrivilegedAction<>() {
-                @Override
-                public Constructor<?>[] run() {
-                    Constructor<?>[] ctrs = innerClass.getDeclaredConstructors();
-                    if (ctrs.length == 1) {
-                        // The lambda implementing inner class constructor is private, set
-                        // it accessible (by us) before creating the constant sole instance
-                        ctrs[0].setAccessible(true);
-                    }
-                    return ctrs;
+            if (disableEagerInitialization) {
+                try {
+                    return new ConstantCallSite(caller.findStaticGetter(innerClass, LAMBDA_INSTANCE_FIELD,
+                            invokedType.returnType()));
+                } catch (ReflectiveOperationException e) {
+                    throw new LambdaConversionException(
+                            "Exception finding " +  LAMBDA_INSTANCE_FIELD + " static field", e);
+                }
+            } else {
+                final Constructor<?>[] ctrs = AccessController.doPrivileged(
+                        new PrivilegedAction<>() {
+                            @Override
+                            public Constructor<?>[] run() {
+                                Constructor<?>[] ctrs = innerClass.getDeclaredConstructors();
+                                if (ctrs.length == 1) {
+                                    // The lambda implementing inner class constructor is private, set
+                                    // it accessible (by us) before creating the constant sole instance
+                                    ctrs[0].setAccessible(true);
+                                }
+                                return ctrs;
+                            }
+                        });
+                if (ctrs.length != 1) {
+                    throw new LambdaConversionException("Expected one lambda constructor for "
+                            + innerClass.getCanonicalName() + ", got " + ctrs.length);
                 }
-                    });
-            if (ctrs.length != 1) {
-                throw new LambdaConversionException("Expected one lambda constructor for "
-                        + innerClass.getCanonicalName() + ", got " + ctrs.length);
-            }
 
-            try {
-                Object inst = ctrs[0].newInstance();
-                return new ConstantCallSite(MethodHandles.constant(samBase, inst));
-            } catch (ReflectiveOperationException e) {
-                throw new LambdaConversionException("Exception instantiating lambda object", e);
+                try {
+                    Object inst = ctrs[0].newInstance();
+                    return new ConstantCallSite(MethodHandles.constant(samBase, inst));
+                } catch (ReflectiveOperationException e) {
+                    throw new LambdaConversionException("Exception instantiating lambda object", e);
+                }
             }
         } else {
             try {
@@ -331,6 +342,10 @@ private Class<?> generateInnerClass() throws LambdaConversionException {
 
         generateConstructor();
 
+        if (invokedType.parameterCount() == 0 && disableEagerInitialization) {
+            generateClassInitializer();
+        }
+
         // Forward the SAM method
         MethodVisitor mv = cw.visitMethod(ACC_PUBLIC, samMethodName,
                                           samMethodType.toMethodDescriptorString(), null, null);
@@ -398,6 +413,32 @@ public Void run() {
         }
     }
 
+    /**
+     * Generate a static field and a static initializer that sets this field to an instance of the lambda
+     */
+    private void generateClassInitializer() {
+        String lambdaTypeDescriptor = invokedType.returnType().descriptorString();
+
+        // Generate the static final field that holds the lambda singleton
+        FieldVisitor fv = cw.visitField(ACC_PRIVATE | ACC_STATIC | ACC_FINAL,
+                LAMBDA_INSTANCE_FIELD, lambdaTypeDescriptor, null, null);
+        fv.visitEnd();
+
+        // Instantiate the lambda and store it to the static final field
+        MethodVisitor clinit = cw.visitMethod(ACC_STATIC, "<clinit>", "()V", null, null);
+        clinit.visitCode();
+
+        clinit.visitTypeInsn(NEW, lambdaClassName);
+        clinit.visitInsn(Opcodes.DUP);
+        assert invokedType.parameterCount() == 0;
+        clinit.visitMethodInsn(INVOKESPECIAL, lambdaClassName, NAME_CTOR, constructorType.toMethodDescriptorString(), false);
+        clinit.visitFieldInsn(PUTSTATIC, lambdaClassName, LAMBDA_INSTANCE_FIELD, lambdaTypeDescriptor);
+
+        clinit.visitInsn(RETURN);
+        clinit.visitMaxs(-1, -1);
+        clinit.visitEnd();
+    }
+
     /**
      * Generate the constructor for the class
      */

test/jdk/java/lang/invoke/lambda/LambdaEagerInitTest.java

@@ -0,0 +1,91 @@
+/*
+ * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/**
+ * @test
+ * @bug 8242451
+ * @library /test/lib
+ * @summary Test that the LAMBDA_INSTANCE$ field is present depending
+ *          on disableEagerInitialization
+ * @run main LambdaEagerInitTest
+ * @run main/othervm -Djdk.internal.lambda.disableEagerInitialization=true LambdaEagerInitTest
+ */
+
+import java.lang.reflect.Field;
+import java.lang.reflect.Modifier;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import static jdk.test.lib.Asserts.*;
+
+public class LambdaEagerInitTest {
+
+    interface H {Object m(String s);}
+
+    private static Set<String> allowedStaticFields(boolean nonCapturing) {
+        Set<String> s = new HashSet<>();
+        if (Boolean.getBoolean("jdk.internal.lambda.disableEagerInitialization")) {
+            if (nonCapturing) s.add("LAMBDA_INSTANCE$");
+        }
+        return s;
+    }
+
+    private void nonCapturingLambda() {
+        H la = s -> s;
+        assertEquals("hi", la.m("hi"));
+        Class<? extends H> c1 = la.getClass();
+        verifyLambdaClass(la.getClass(), true);
+    }
+
+    private void capturingLambda() {
+        H la = s -> concat(s, "foo");
+        assertEquals("hi foo", la.m("hi"));
+        verifyLambdaClass(la.getClass(), false);
+    }
+
+    private void verifyLambdaClass(Class<?> c, boolean nonCapturing) {
+        Set<String> staticFields = new HashSet<>();
+        Set<String> instanceFields = new HashSet<>();
+        for (Field f : c.getDeclaredFields()) {
+            if (Modifier.isStatic(f.getModifiers())) {
+                staticFields.add(f.getName());
+            } else {
+                instanceFields.add(f.getName());
+            }
+        }
+        assertEquals(instanceFields.size(), nonCapturing ? 0 : 1, "Unexpected instance fields");
+        assertEquals(staticFields, allowedStaticFields(nonCapturing), "Unexpected static fields");
+    }
+
+    private String concat(String... ss) {
+        return Arrays.stream(ss).collect(Collectors.joining(" "));
+    }
+
+    public static void main(String[] args) {
+        LambdaEagerInitTest test = new LambdaEagerInitTest();
+        test.nonCapturingLambda();
+        test.capturingLambda();
+    }
+}

test/langtools/tools/javac/lambda/lambdaExpression/LambdaTest6.java

@@ -26,11 +26,9 @@
  * @bug 8003280
  * @summary Add lambda tests
  *   Test bridge methods for certain SAM conversions
- *   Tests that jdk.internal.lambda.disableEagerInitialization=true creates a
- *   get$Lambda method for non-capturing lambdas
+ *   Test the set of generated methods
  * @compile LambdaTest6.java
  * @run main LambdaTest6
- * @run main/othervm -Djdk.internal.lambda.disableEagerInitialization=true LambdaTest6
  */
 
 import java.lang.reflect.Method;

test/langtools/tools/javac/lambda/methodReference/BridgeMethod.java

@@ -26,15 +26,11 @@
  * @bug 8003280
  * @summary Add lambda tests
  *   Test bridge methods in certain SAM conversion
- *   Tests that jdk.internal.lambda.disableEagerInitialization=true creates a
- *   get$Lambda method for non-capturing lambdas
  * @compile BridgeMethod.java
  * @run main BridgeMethod
- * @run main/othervm -Djdk.internal.lambda.disableEagerInitialization=true BridgeMethod
  */
 
 import java.lang.reflect.Method;
-import java.util.Arrays;
 import java.util.HashSet;
 import java.util.Set;
 
@@ -72,52 +68,34 @@ private static Set<String> setOfStringObject() {
         return s;
     }
 
-    private static Set<String> allowedMethods() {
-        Set<String> s = new HashSet<>();
-        s.add("m");
-        return s;
-    }
-
-    private static boolean matchingMethodNames(Method[] methods) {
-        Set<String> methodNames = new HashSet<>();
-        for (Method m : methods) {
-            methodNames.add(m.getName());
-        }
-        return methodNames.equals(allowedMethods());
-    }
-
     public static void main(String[] args) {
         L la = BridgeMethod::bar; //static reference
         la.m("hi");
         Class<? extends L> c1 = la.getClass();
         Method[] methods = c1.getDeclaredMethods();
-        assertTrue(matchingMethodNames(methods));
         Set<String> types = setOfStringObject();
         System.out.println("methods in SAM conversion of L:");
         for(Method m : methods) {
-            if (m.getName().equals("m")) {
-                System.out.println(m.toGenericString());
-                Class[] parameterTypes = m.getParameterTypes();
-                assertTrue(parameterTypes.length == 1);
-                assertTrue(types.remove(parameterTypes[0].getName()));
-            }
+            assertTrue(m.getName().equals("m"));
+            System.out.println(m.toGenericString());
+            Class[] parameterTypes = m.getParameterTypes();
+            assertTrue(parameterTypes.length == 1);
+            assertTrue(types.remove(parameterTypes[0].getName()));
         }
         assertTrue(types.isEmpty() || (types.size() == 1 && types.contains("java.lang.String")));
 
         KM km = BridgeMethod::bar;
         //km.m("hi"); //will be uncommented when CR7028808 fixed
         Class<? extends KM> c2 = km.getClass();
         methods = c2.getDeclaredMethods();
-        assertTrue(matchingMethodNames(methods));
         types = setOfStringObject();
         System.out.println("methods in SAM conversion of KM:");
         for(Method m : methods) {
-            if (m.getName().equals("m")) {
-                System.out.println(m.toGenericString());
-                Class<?>[] parameterTypes = m.getParameterTypes();
-                assertTrue(parameterTypes.length == 1);
-                assertTrue(types.remove(parameterTypes[0].getName()));
-            }
+            assertTrue(m.getName().equals("m"));
+            System.out.println(m.toGenericString());
+            Class<?>[] parameterTypes = m.getParameterTypes();
+            assertTrue(parameterTypes.length == 1);
+            assertTrue(types.remove(parameterTypes[0].getName()));
         }
         assertTrue(types.isEmpty());