src/java.base/share/classes/java/util/concurrent/atomic/Striped64.java

8192943: Optimize atomic accumulators using VarHandle getAndSet
Reviewed-by: martin, psandoz, chegar

@@ -131,10 +131,13 @@
             VALUE.setVolatile(this, 0L);
         }
         final void reset(long identity) {
             VALUE.setVolatile(this, identity);
         }
+        final long getAndSet(long val) {
+            return (long)VALUE.getAndSet(this, val);
+        }
 
         // VarHandle mechanics
         private static final VarHandle VALUE;
         static {
             try {

@@ -176,10 +179,14 @@
      */
     final boolean casBase(long cmp, long val) {
         return BASE.compareAndSet(this, cmp, val);
     }
 
+    final long getAndSetBase(long val) {
+        return (long)BASE.getAndSet(this, val);
+    }
+
     /**
      * CASes the cellsBusy field from 0 to 1 to acquire lock.
      */
     final boolean casCellsBusy() {
         return CELLSBUSY.compareAndSet(this, 0, 1);

@@ -226,13 +233,13 @@
             h = getProbe();
             wasUncontended = true;
         }
         boolean collide = false;                // True if last slot nonempty
         done: for (;;) {
-            Cell[] as; Cell a; int n; long v;
-            if ((as = cells) != null && (n = as.length) > 0) {
-                if ((a = as[(n - 1) & h]) == null) {
+            Cell[] cs; Cell c; int n; long v;
+            if ((cs = cells) != null && (n = cs.length) > 0) {
+                if ((c = cs[(n - 1) & h]) == null) {
                     if (cellsBusy == 0) {       // Try to attach new Cell
                         Cell r = new Cell(x);   // Optimistically create
                         if (cellsBusy == 0 && casCellsBusy()) {
                             try {               // Recheck under lock
                                 Cell[] rs; int m, j;

@@ -250,32 +257,32 @@
                     }
                     collide = false;
                 }
                 else if (!wasUncontended)       // CAS already known to fail
                     wasUncontended = true;      // Continue after rehash
-                else if (a.cas(v = a.value,
+                else if (c.cas(v = c.value,
                                (fn == null) ? v + x : fn.applyAsLong(v, x)))
                     break;
-                else if (n >= NCPU || cells != as)
+                else if (n >= NCPU || cells != cs)
                     collide = false;            // At max size or stale
                 else if (!collide)
                     collide = true;
                 else if (cellsBusy == 0 && casCellsBusy()) {
                     try {
-                        if (cells == as)        // Expand table unless stale
-                            cells = Arrays.copyOf(as, n << 1);
+                        if (cells == cs)        // Expand table unless stale
+                            cells = Arrays.copyOf(cs, n << 1);
                     } finally {
                         cellsBusy = 0;
                     }
                     collide = false;
                     continue;                   // Retry with expanded table
                 }
                 h = advanceProbe(h);
             }
-            else if (cellsBusy == 0 && cells == as && casCellsBusy()) {
+            else if (cellsBusy == 0 && cells == cs && casCellsBusy()) {
                 try {                           // Initialize table
-                    if (cells == as) {
+                    if (cells == cs) {
                         Cell[] rs = new Cell[2];
                         rs[h & 1] = new Cell(x);
                         cells = rs;
                         break done;
                     }

@@ -310,13 +317,13 @@
             h = getProbe();
             wasUncontended = true;
         }
         boolean collide = false;                // True if last slot nonempty
         done: for (;;) {
-            Cell[] as; Cell a; int n; long v;
-            if ((as = cells) != null && (n = as.length) > 0) {
-                if ((a = as[(n - 1) & h]) == null) {
+            Cell[] cs; Cell c; int n; long v;
+            if ((cs = cells) != null && (n = cs.length) > 0) {
+                if ((c = cs[(n - 1) & h]) == null) {
                     if (cellsBusy == 0) {       // Try to attach new Cell
                         Cell r = new Cell(Double.doubleToRawLongBits(x));
                         if (cellsBusy == 0 && casCellsBusy()) {
                             try {               // Recheck under lock
                                 Cell[] rs; int m, j;

@@ -334,31 +341,31 @@
                     }
                     collide = false;
                 }
                 else if (!wasUncontended)       // CAS already known to fail
                     wasUncontended = true;      // Continue after rehash
-                else if (a.cas(v = a.value, apply(fn, v, x)))
+                else if (c.cas(v = c.value, apply(fn, v, x)))
                     break;
-                else if (n >= NCPU || cells != as)
+                else if (n >= NCPU || cells != cs)
                     collide = false;            // At max size or stale
                 else if (!collide)
                     collide = true;
                 else if (cellsBusy == 0 && casCellsBusy()) {
                     try {
-                        if (cells == as)        // Expand table unless stale
-                            cells = Arrays.copyOf(as, n << 1);
+                        if (cells == cs)        // Expand table unless stale
+                            cells = Arrays.copyOf(cs, n << 1);
                     } finally {
                         cellsBusy = 0;
                     }
                     collide = false;
                     continue;                   // Retry with expanded table
                 }
                 h = advanceProbe(h);
             }
-            else if (cellsBusy == 0 && cells == as && casCellsBusy()) {
+            else if (cellsBusy == 0 && cells == cs && casCellsBusy()) {
                 try {                           // Initialize table
-                    if (cells == as) {
+                    if (cells == cs) {
                         Cell[] rs = new Cell[2];
                         rs[h & 1] = new Cell(Double.doubleToRawLongBits(x));
                         cells = rs;
                         break done;
                     }