Merge pull request #759 from nbhuiyan/vh-cas

Use Unsafe.compareAndExchange for writing to Stable field and array

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

@@ -23,9 +23,16 @@
  * questions.
  */
 
+/*
+ * ===========================================================================
+ * (c) Copyright IBM Corp. 2024, 2024 All Rights Reserved
+ * ===========================================================================
+ */
+
 package java.lang.invoke;
 
 import jdk.internal.HotSpotIntrinsicCandidate;
+import jdk.internal.misc.Unsafe;
 import jdk.internal.util.Preconditions;
 import jdk.internal.vm.annotation.ForceInline;
 import jdk.internal.vm.annotation.Stable;
@@ -1964,11 +1971,22 @@ static class TypesAndInvokers {
  new MethodHandle[AccessMode.values().length];
  }
 
+ 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.compareAndExchangeObject(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;
  }
@@ -1978,7 +1996,13 @@ final 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.compareAndExchangeObject(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;
  }