Merge pull request #325 from nbhuiyan/vh-cas

Use Unsafe.compareAndSwap for writing to Stable field and array

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

@@ -23,6 +23,12 @@
  * questions.
  */
 
+/*
+ * ===========================================================================
+ * (c) Copyright IBM Corp. 2024, 2024 All Rights Reserved
+ * ===========================================================================
+ */
+
 package java.lang.invoke;
 
 import java.lang.constant.ClassDesc;
@@ -39,6 +45,7 @@
 import java.util.function.BiFunction;
 import java.util.function.Function;
 
+import jdk.internal.misc.Unsafe;
 import jdk.internal.util.Preconditions;
 import jdk.internal.vm.annotation.DontInline;
 import jdk.internal.vm.annotation.ForceInline;
@@ -2140,11 +2147,22 @@ static class TypesAndInvokers {
  MethodHandle[] methodHandle_table = new MethodHandle[AccessMode.COUNT];
  }
 
+ private static final long TYPES_AND_INVOKERS_OFFSET;
+
+ static {
+ TYPES_AND_INVOKERS_OFFSET = UNSAFE.objectFieldOffset(VarHandle.class, "typesAndInvokers");
+ }
+
  @ForceInline
  private final TypesAndInvokers getTypesAndInvokers() {
  TypesAndInvokers tis = typesAndInvokers;
  if (tis == null) {
- tis = typesAndInvokers = new TypesAndInvokers();
+ tis = new TypesAndInvokers();
+ Object other = UNSAFE.compareAndExchangeReference(this, TYPES_AND_INVOKERS_OFFSET, null, tis);
+ if (other != null) {
+ // Lost the race, so use what was set by winning thread.
+ tis = (TypesAndInvokers) other;
+ }
  }
  return tis;
  }
@@ -2154,7 +2172,13 @@ MethodHandle getMethodHandle(int mode) {
  TypesAndInvokers tis = getTypesAndInvokers();
  MethodHandle mh = tis.methodHandle_table[mode];
  if (mh == null) {
- mh = tis.methodHandle_table[mode] = getMethodHandleUncached(mode);
+ mh = getMethodHandleUncached(mode);
+ long offset = Unsafe.ARRAY_OBJECT_BASE_OFFSET + (Unsafe.ARRAY_OBJECT_INDEX_SCALE * mode);
+ Object other = UNSAFE.compareAndExchangeReference(tis.methodHandle_table, offset, null, mh);
+ if (other != null) {
+ // We lost the race. Use the winning thread's handle instead.
+ mh = (MethodHandle) other;
+ }
  }
  return mh;
  }