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.
Regards, Peter
