On 06/25/2013 11:38 PM, Peter Levart wrote:
>
> On 06/25/2013 09:12 PM, Aleksey Shipilev wrote:
>> It might be a good idea to turn $powerCache final, not volatile, since
>> the code will recover anyway. The trouble I'm seeing is weak enough
>> hardware, which will never see the updated value of cacheLine, always
>> falling back. Hence, I'm keen to keep "volatile".
>
> The worst thing that could happen is that each thread would effectively
> have it's private cache.
Right.
That only works if you store the fallback value to cacheLine, and then
back to powerCache, since the second get...() will possibly re-read the
stale cacheLine otherwise. Your version did that. Do we want to store
the retVal?
private static final BigInteger[][] powerCache;
BigInteger getRadixConversionCache(int radix, int exponent) {
BigInteger retVal = null;
BigInteger[][] pc = powerCache;
BigInteger[] cacheLine = pc[radix];
int oldSize = cacheLine.length;
if (exponent >= oldSize) {
cacheLine = Arrays.copyOf(cacheLine, exponent + 1);
for (int i = oldSize; i <= exponent; i++) {
retVal = cacheLine[i - 1].square();
cacheLine[i] = retVal;
}
pc[radix] = cacheLine;
} else {
retVal = cacheLine[exponent];
if (retVal == null) {
// data race, element is not available yet,
// compute on the fly
retVal = BigInteger.valueOf(radix);
for (int c = 0; c < exponent; c++) {
retVal = retVal.square();
}
cacheLine[exponent] = retVal;
}
}
-Aleksey.
