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6948537: CMS: BOT walkers observe out-of-thin-air zeros on sun4v sparc/CMT

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On sun4v/CMT avoid use of memset() in BOT updates so as to prevent concurrent BOT readers from seeing the phantom zeros arising from memset()'s use of BIS.

Reviewed-by: jmasa, johnc, minqi, poonam, tonyp
This commit is contained in:
Y. Srinivas Ramakrishna 2010-05-03 10:24:51 -07:00
parent 99196ff9ca
commit 762f60d343
4 changed files with 44 additions and 2 deletions
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8
hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp
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@ -789,6 +789,14 @@ CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
_gc_counters = new CollectorCounters("CMS", 1);
_completed_initialization = true;
_inter_sweep_timer.start(); // start of time
#ifdef SPARC
// Issue a stern warning, but allow use for experimentation and debugging.
if (VM_Version::is_sun4v() && UseMemSetInBOT) {
assert(!FLAG_IS_DEFAULT(UseMemSetInBOT), "Error");
warning("Experimental flag -XX:+UseMemSetInBOT is known to cause instability"
" on sun4v; please understand that you are using at your own risk!");
}
#endif
}
const char* ConcurrentMarkSweepGeneration::name() const {