src/share/vm/memory/genCollectedHeap.cpp
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rev 2870 : 7117303: VM uses non-monotonic time source and complains that it is non-monotonic
Summary: Replaces calls to os::javaTimeMillis(), which does not guarantee montonicity, in GC code to os::javaTimeNanos() with a suitable conversion factor. os::javaTimeNanos is guaranteed monotonic if the underlying platform provides a monotonic timesource. Changes in OS files are to make use of the newly defined constants in globalDefinitions.hpp.
Reviewed-by: dholmes
@@ -1458,29 +1458,25 @@
_time = MIN2(_time, gen->time_of_last_gc(_now));
}
};
jlong GenCollectedHeap::millis_since_last_gc() {
- jlong now = os::javaTimeMillis();
+ // We need a montonically increasing time in ms but os::javaTimeMillis()
+ // does not guarantee montonicity.
+ jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
GenTimeOfLastGCClosure tolgc_cl(now);
// iterate over generations getting the oldest
// time that a generation was collected
generation_iterate(&tolgc_cl, false);
tolgc_cl.do_generation(perm_gen());
- // XXX Despite the assert above, since javaTimeMillis()
- // doesnot guarantee monotonically increasing return
- // values (note, i didn't say "strictly monotonic"),
- // we need to guard against getting back a time
- // later than now. This should be fixed by basing
- // on someting like gethrtime() which guarantees
- // monotonicity. Note that cond_wait() is susceptible
- // to a similar problem, because its interface is
- // based on absolute time in the form of the
- // system time's notion of UCT. See also 4506635
- // for yet another problem of similar nature. XXX
+
+ // javaTimeNanos() is guaranteed to be monotonically non-decreasing
+ // provided the underlying platform provides such a time source
+ // (and it is bug free). So we still have to guard against getting
+ // back a time later than 'now'.
jlong retVal = now - tolgc_cl.time();
if (retVal < 0) {
- NOT_PRODUCT(warning("time warp: %d", retVal);)
+ NOT_PRODUCT(warning("time warp: "INT64_FORMAT, retVal);)
return 0;
}
return retVal;
}