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

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

*** 85,103 ****
       * Adds the given value.
       *
       * @param x the value to add
       */
      public void add(double x) {
!         Cell[] as; long b, v; int m; Cell a;
!         if ((as = cells) != null ||
              !casBase(b = base,
                       Double.doubleToRawLongBits
                       (Double.longBitsToDouble(b) + x))) {
              boolean uncontended = true;
!             if (as == null || (m = as.length - 1) < 0 ||
!                 (a = as[getProbe() & m]) == null ||
!                 !(uncontended = a.cas(v = a.value,
                                        Double.doubleToRawLongBits
                                        (Double.longBitsToDouble(v) + x))))
                  doubleAccumulate(x, null, uncontended);
          }
      }
--- 85,103 ----
       * Adds the given value.
       *
       * @param x the value to add
       */
      public void add(double x) {
!         Cell[] cs; long b, v; int m; Cell c;
!         if ((cs = cells) != null ||
              !casBase(b = base,
                       Double.doubleToRawLongBits
                       (Double.longBitsToDouble(b) + x))) {
              boolean uncontended = true;
!             if (cs == null || (m = cs.length - 1) < 0 ||
!                 (c = cs[getProbe() & m]) == null ||
!                 !(uncontended = c.cas(v = c.value,
                                        Double.doubleToRawLongBits
                                        (Double.longBitsToDouble(v) + x))))
                  doubleAccumulate(x, null, uncontended);
          }
      }
*** 113,128 ****
       * updates to a single variable.
       *
       * @return the sum
       */
      public double sum() {
!         Cell[] as = cells;
          double sum = Double.longBitsToDouble(base);
!         if (as != null) {
!             for (Cell a : as)
!                 if (a != null)
!                     sum += Double.longBitsToDouble(a.value);
          }
          return sum;
      }
  
      /**
--- 113,128 ----
       * updates to a single variable.
       *
       * @return the sum
       */
      public double sum() {
!         Cell[] cs = cells;
          double sum = Double.longBitsToDouble(base);
!         if (cs != null) {
!             for (Cell c : cs)
!                 if (c != null)
!                     sum += Double.longBitsToDouble(c.value);
          }
          return sum;
      }
  
      /**
*** 131,146 ****
       * effective if there are no concurrent 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 = 0L; // relies on fact that double 0 must have same rep as long
!         if (as != null) {
!             for (Cell a : as)
!                 if (a != null)
!                     a.reset();
          }
      }
  
      /**
       * Equivalent in effect to {@link #sum} followed by {@link
--- 131,146 ----
       * effective if there are no concurrent 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 = 0L; // relies on fact that double 0 must have same rep as long
!         if (cs != null) {
!             for (Cell c : cs)
!                 if (c != null)
!                     c.reset();
          }
      }
  
      /**
       * Equivalent in effect to {@link #sum} followed by {@link
*** 151,170 ****
       * the reset.
       *
       * @return the sum
       */
      public double sumThenReset() {
!         Cell[] as = cells;
!         double sum = Double.longBitsToDouble(base);
!         base = 0L;
!         if (as != null) {
!             for (Cell a : as) {
!                 if (a != null) {
!                     long v = a.value;
!                     a.reset();
!                     sum += Double.longBitsToDouble(v);
!                 }
              }
          }
          return sum;
      }
  
--- 151,166 ----
       * the reset.
       *
       * @return the sum
       */
      public double sumThenReset() {
!         Cell[] cs = cells;
!         double sum = Double.longBitsToDouble(getAndSetBase(0L));
!         if (cs != null) {
!             for (Cell c : cs) {
!                 if (c != null)
!                     sum += Double.longBitsToDouble(c.getAndSet(0L));
              }
          }
          return sum;
      }