8014509: @Contended: explicit default value behaves differently from the implicit value

Summary: Treat the empty string as the default value tag
Reviewed-by: kvn, twisti

src/share/vm/classfile/classFileParser.cpp

@@ -1719,15 +1719,28 @@ void ClassFileParser::parse_annotations(u1* buffer, int limit,
     coll->set_annotation(id);
 
     if (id == AnnotationCollector::_sun_misc_Contended) {
+      // @Contended can optionally specify the contention group.
+      //
+      // Contended group defines the equivalence class over the fields:
+      // the fields within the same contended group are not treated distinct.
+      // The only exception is default group, which does not incur the
+      // equivalence. Naturally, contention group for classes is meaningless.
+      //
+      // While the contention group is specified as String, annotation
+      // values are already interned, and we might as well use the constant
+      // pool index as the group tag.
+      //
+      u2 group_index = 0; // default contended group
       if (count == 1
           && s_size == (index - index0)  // match size
           && s_tag_val == *(abase + tag_off)
           && member == vmSymbols::value_name()) {
-        u2 group_index = Bytes::get_Java_u2(abase + s_con_off);
-        coll->set_contended_group(group_index);
-      } else {
-        coll->set_contended_group(0); // default contended group
+        group_index = Bytes::get_Java_u2(abase + s_con_off);
+        if (_cp->symbol_at(group_index)->utf8_length() == 0) {
+          group_index = 0; // default contended group
+        }
       }
+      coll->set_contended_group(group_index);
     }
   }
 }

test/runtime/contended/DefaultValue.java

+/*
+ * Copyright (c) 2013, 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.
+ */
+
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.lang.Class;
+import java.lang.String;
+import java.lang.System;
+import java.lang.management.ManagementFactory;
+import java.lang.management.RuntimeMXBean;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.CyclicBarrier;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+import java.lang.reflect.Field;
+import java.lang.reflect.Modifier;
+import sun.misc.Unsafe;
+import sun.misc.Contended;
+
+/*
+ * @test
+ * @bug     8014509
+ * @summary \@Contended: explicit default value behaves differently from the implicit value
+ *
+ * @run main/othervm -XX:-RestrictContended DefaultValue
+ */
+public class DefaultValue {
+
+    private static final Unsafe U;
+    private static int ADDRESS_SIZE;
+    private static int HEADER_SIZE;
+
+    static {
+        // steal Unsafe
+        try {
+            Field unsafe = Unsafe.class.getDeclaredField("theUnsafe");
+            unsafe.setAccessible(true);
+            U = (Unsafe) unsafe.get(null);
+        } catch (NoSuchFieldException | IllegalAccessException e) {
+            throw new IllegalStateException(e);
+        }
+
+        // When running with CompressedOops on 64-bit platform, the address size
+        // reported by Unsafe is still 8, while the real reference fields are 4 bytes long.
+        // Try to guess the reference field size with this naive trick.
+        try {
+            long off1 = U.objectFieldOffset(CompressedOopsClass.class.getField("obj1"));
+            long off2 = U.objectFieldOffset(CompressedOopsClass.class.getField("obj2"));
+            ADDRESS_SIZE = (int) Math.abs(off2 - off1);
+            HEADER_SIZE = (int) Math.min(off1, off2);
+        } catch (NoSuchFieldException e) {
+            ADDRESS_SIZE = -1;
+        }
+    }
+
+    static class CompressedOopsClass {
+        public Object obj1;
+        public Object obj2;
+    }
+
+    public static boolean arePaddedPairwise(Class klass, String field1, String field2) throws Exception {
+        Field f1 = klass.getField(field1);
+        Field f2 = klass.getField(field2);
+
+        int diff = offset(f1) - offset(f2);
+        if (diff < 0) {
+            // f1 is first
+            return (offset(f2) - (offset(f1) + getSize(f1))) > 64;
+        } else {
+            // f2 is first
+            return (offset(f1) - (offset(f2) + getSize(f2))) > 64;
+        }
+    }
+
+    public static boolean sameLayout(Class klass1, Class klass2) throws Exception {
+        for (Field f1 : klass1.getDeclaredFields()) {
+            Field f2 = klass2.getDeclaredField(f1.getName());
+            if (offset(f1) != offset(f2)) {
+                return false;
+            }
+        }
+
+        for (Field f2 : klass1.getDeclaredFields()) {
+            Field f1 = klass2.getDeclaredField(f2.getName());
+            if (offset(f1) != offset(f2)) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    public static boolean isStatic(Field field) {
+        return Modifier.isStatic(field.getModifiers());
+    }
+
+    public static int offset(Field field) {
+        if (isStatic(field)) {
+            return (int) U.staticFieldOffset(field);
+        } else {
+            return (int) U.objectFieldOffset(field);
+        }
+    }
+
+    public static int getSize(Field field) {
+        Class type = field.getType();
+        if (type == byte.class)    { return 1; }
+        if (type == boolean.class) { return 1; }
+        if (type == short.class)   { return 2; }
+        if (type == char.class)    { return 2; }
+        if (type == int.class)     { return 4; }
+        if (type == float.class)   { return 4; }
+        if (type == long.class)    { return 8; }
+        if (type == double.class)  { return 8; }
+        return ADDRESS_SIZE;
+    }
+
+    public static void main(String[] args) throws Exception {
+        boolean endResult = true;
+
+        if (!arePaddedPairwise(R1.class, "int1", "int2")) {
+            System.err.println("R1 failed");
+            endResult &= false;
+        }
+
+        if (!arePaddedPairwise(R2.class, "int1", "int2")) {
+            System.err.println("R2 failed");
+            endResult &= false;
+        }
+
+        if (!arePaddedPairwise(R3.class, "int1", "int2")) {
+            System.err.println("R3 failed");
+            endResult &= false;
+        }
+
+        System.out.println(endResult ? "Test PASSES" : "Test FAILS");
+        if (!endResult) {
+           throw new Error("Test failed");
+        }
+    }
+
+    public static class R1 {
+        @Contended
+        public int int1;
+        @Contended
+        public int int2;
+    }
+
+    public static class R2 {
+        @Contended("")
+        public int int1;
+        @Contended("")
+        public int int2;
+    }
+
+    public static class R3 {
+        @Contended()
+        public int int1;
+        @Contended()
+        public int int2;
+    }
+
+}
+