RFR 8005311: Add Scalable Updatable Variables, DoubleAccumulator, DoubleAdder, LongAccumulator, LongAdder (original) (raw)

Remi Forax forax at univ-mlv.fr
Sat Jan 5 23:42:35 UTC 2013

On 01/05/2013 07:10 PM, Chris Hegarty wrote:

As part of JEP 155 we are proposing to add the following public classes to support Scalable Updatable Variables, DoubleAccumulator, DoubleAdder, LongAccumulator and LongAdder.

These have been written by Doug Lea, with assistance from members of the former JCP JSR-166 Expert Group. Webrev and javadoc are at: http://cr.openjdk.java.net/~chegar/8005311/ver.00/ Since Doug is the author, I am taking a reviewer/sponsor role. Here are my initial comments. - There are various places in DoubleAccmulator where there are broken links to #sum ( I think it is just a cut'n'paste error ). These should be #get. - Accumulators {@link #get} may read somewhat better as {@link #get current value} ?? - Accumulators Does the 'identity' value need further explanation? Note: There is one minor change to the implementation. Currently in the jdk8 repo j.u.f.DoubleBinaryOperator defines operateAsDouble. This method has been renamed to applyAsDouble in the lambda/lambda repo. When these changes are sync'ed from lambda/lambda this can be reverted. A similar comment has been added to the code. -Chris.

The code is not very java-ish, by example, in Striped64,

Cell[] as; Cell a; int n; long v; if ((as = cells) != null && (n = as.length) > 0) { if ((a = as[(n - 1) & h]) == null) {

instead

int n; Cell[] as = cells; if (as != null && (n = as.length) > 0) { Cell a = as[(n - 1) & h]; if ((a == null) {

also I think that the variable created (and 'init' after in the code) are not needed.

boolean created = false; try { // Recheck under lock Cell[] rs; int m, j; if ((rs = cells) != null && (m = rs.length) > 0 && rs[j = (m - 1) & h] == null) { rs[j] = r; created = true; } } finally { cellsBusy = 0; } if (created) break;

The code can become

try { // Recheck under lock Cell[] rs = cells; int m, j; if (rs != null && (m = rs.length) > 0 && rs[j = (m - 1) & h] == null) { rs[j] = r; break; } } finally { cellsBusy = 0; }

Overall, I think there are too many lazy initializations. Unlike HashMap, if a developer uses let say LongAccumulator it's because AtomicLong doesn't work well, so not having the array of cells initialized by default seems weird.

Rémi

More information about the core-libs-dev mailing list