RFR 8226543 : Reduce GC pressure during message digest calculations in password-based encryption

[Ivan Gerasimov]

Hello!

In PBES1Core.deriveCipherKey() there are loops that look like following:

            for (int i = 0; i < iCount; i++) {
                md.update(toBeHashed);
                toBeHashed = md.digest(); // this resets the digest
            }

Calling md.digest() each time allocates a new byte[] array.
It would be more GC friendly, if the same array were reused.

In the fix, a first call to md.digest() allocates a properly sized array.
Subsequent iterations reuse this array.

Would you please help review?

BUGURL: https://bugs.openjdk.java.net/browse/JDK-8226543
WEBREV: http://cr.openjdk.java.net/~igerasim/8226543/00/webrev/

No new regression test, as the behavior was not changed.
Mach5 control job is green (tiers 1-4 on all supported platforms).

--
With kind regards,
Ivan Gerasimov