RFR 8017540: Improve multi-threaded contention behavior of BigInteger.toString() radix conversion cache (original) (raw)

Aleksey Shipilev aleksey.shipilev at oracle.com
Tue Jun 25 19:53:27 UTC 2013

On 06/25/2013 11:36 PM, Dmitry Nadezhin wrote:

What about such code ?

BigInteger getRadixConversionCache(int radix, int exponent) { BigInteger retVal = null; BigInteger[][] pc = powerCache; // volatile read 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; } synchronized (pc) { if (pc[radix].length < cacheLine.length) { pc[radix] = cacheLine; powerCache = pc; // volatile write, publish } } } else { retVal = cacheLine[exponent]; } return retVal; }

Still the same race. The reader thread sees the full-length cacheLine early, but the elements are not yet there.

Is dummy volatile write necessary inside synchronized block ? powerCache = pc; // volatile write, publish

Yes, since you need to have the matched synchronized(pc) otherwise to produce the pairwise "acquire".

-Aleksey.

More information about the core-libs-dev mailing list