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

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

*** 101,121 ****
       * Updates with the given value.
       *
       * @param x the value
       */
      public void accumulate(long x) {
!         Cell[] as; long b, v, r; int m; Cell a;
!         if ((as = cells) != null
              || ((r = function.applyAsLong(b = base, x)) != b
                  && !casBase(b, r))) {
              boolean uncontended = true;
!             if (as == null
!                 || (m = as.length - 1) < 0
!                 || (a = as[getProbe() & m]) == null
                  || !(uncontended =
!                      (r = function.applyAsLong(v = a.value, x)) == v
!                      || a.cas(v, r)))
                  longAccumulate(x, function, uncontended);
          }
      }
  
      /**
--- 101,121 ----
       * Updates with the given value.
       *
       * @param x the value
       */
      public void accumulate(long x) {
!         Cell[] cs; long b, v, r; int m; Cell c;
!         if ((cs = cells) != null
              || ((r = function.applyAsLong(b = base, x)) != b
                  && !casBase(b, r))) {
              boolean uncontended = true;
!             if (cs == null
!                 || (m = cs.length - 1) < 0
!                 || (c = cs[getProbe() & m]) == null
                  || !(uncontended =
!                      (r = function.applyAsLong(v = c.value, x)) == v
!                      || c.cas(v, r)))
                  longAccumulate(x, function, uncontended);
          }
      }
  
      /**
*** 126,141 ****
       * incorporated.
       *
       * @return the current value
       */
      public long get() {
!         Cell[] as = cells;
          long result = base;
!         if (as != null) {
!             for (Cell a : as)
!                 if (a != null)
!                     result = function.applyAsLong(result, a.value);
          }
          return result;
      }
  
      /**
--- 126,141 ----
       * incorporated.
       *
       * @return the current value
       */
      public long get() {
!         Cell[] cs = cells;
          long result = base;
!         if (cs != null) {
!             for (Cell c : cs)
!                 if (c != null)
!                     result = function.applyAsLong(result, c.value);
          }
          return result;
      }
  
      /**
*** 145,160 ****
       * updates.  Because this method is intrinsically racy, it should
       * only be used when it is known that no threads are concurrently
       * updating.
       */
      public void reset() {
!         Cell[] as = cells;
          base = identity;
!         if (as != null) {
!             for (Cell a : as)
!                 if (a != null)
!                     a.reset(identity);
          }
      }
  
      /**
       * Equivalent in effect to {@link #get} followed by {@link
--- 145,160 ----
       * updates.  Because this method is intrinsically racy, it should
       * only be used when it is known that no threads are concurrently
       * updating.
       */
      public void reset() {
!         Cell[] cs = cells;
          base = identity;
!         if (cs != null) {
!             for (Cell c : cs)
!                 if (c != null)
!                     c.reset(identity);
          }
      }
  
      /**
       * Equivalent in effect to {@link #get} followed by {@link
*** 165,182 ****
       * the reset.
       *
       * @return the value before reset
       */
      public long getThenReset() {
!         Cell[] as = cells;
!         long result = base;
!         base = identity;
!         if (as != null) {
!             for (Cell a : as) {
!                 if (a != null) {
!                     long v = a.value;
!                     a.reset(identity);
                      result = function.applyAsLong(result, v);
                  }
              }
          }
          return result;
--- 165,180 ----
       * the reset.
       *
       * @return the value before reset
       */
      public long getThenReset() {
!         Cell[] cs = cells;
!         long result = getAndSetBase(identity);
!         if (cs != null) {
!             for (Cell c : cs) {
!                 if (c != null) {
!                     long v = c.getAndSet(identity);
                      result = function.applyAsLong(result, v);
                  }
              }
          }
          return result;