On Feb 27, 2014, at 8:02 PM, Peter Levart <peter.lev...@gmail.com> wrote:
> > On 02/27/2014 04:06 PM, Paul Sandoz wrote: >>> > Back then I presented an alternative solution which solves that: >>> > >>> > http://mail.openjdk.java.net/pipermail/core-libs-dev/2013-June/018457.html >>> > >>> > ...and as can be seen, does not use volatile read/write to publish >>> > BigIntegers - that's why it is important that internal implementation of >>> > such immutable classes like BigInteger is tolerant to unsafe >>> > publication... >>> > >> Interesting, nice use of a linked list. Not sure that is safe publication of >> cacheLine into powerCache, the last element in a line could be observed as >> null, plus although it is unlikely, the compiler could shuffle up the array >> element store? > > Hi Paul, > > Any element of powerCacheIndex array of arrays and/or any element of it's > BigInteger[] sub-arrays can be observed as null and the code accounts for > that. You can view the scheme as two-level cache. The 1st level is > 'powerCacheIndex' where BigInteger[]s and BigIntegers are published unsafely. > If non-null values are observed, they are correct, if null values are > observed, the code looks through into the 2nd level 'powerCache' array of > linked-lists which is a properly synchronized lazily initialized cache of > values where each is calculated at most once. > Doh! i somehow missed that null check, thanks, i get it now. Paul.
