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7117303: VM uses non-monotonic time source and complains that it is non-monotonic

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Replaces calls to os::javaTimeMillis(), which does not (and cannot) guarantee monotonicity, in GC code to an equivalent expression that uses os::javaTimeNanos(). os::javaTimeNanos is guaranteed monotonically non-decreasing if the underlying platform provides a monotonic time source. Changes in OS files are to make use of the newly defined constants in globalDefinitions.hpp.

Reviewed-by: dholmes, ysr
This commit is contained in:
John Cuthbertson 2011-12-19 10:02:05 -08:00
parent 2768349b41
commit 870bea622a
10 changed files with 57 additions and 57 deletions
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18
hotspot/src/share/vm/memory/referenceProcessor.cpp
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@ -43,7 +43,9 @@ void referenceProcessor_init() {
}
void ReferenceProcessor::init_statics() {
jlong now = os::javaTimeMillis();
// We need a monotonically non-deccreasing time in ms but
// os::javaTimeMillis() does not guarantee monotonicity.
jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
// Initialize the soft ref timestamp clock.
_soft_ref_timestamp_clock = now;
@ -151,7 +153,10 @@ void ReferenceProcessor::weak_oops_do(OopClosure* f) {
void ReferenceProcessor::update_soft_ref_master_clock() {
// Update (advance) the soft ref master clock field. This must be done
// after processing the soft ref list.
jlong now = os::javaTimeMillis();
// We need a monotonically non-deccreasing time in ms but
// os::javaTimeMillis() does not guarantee monotonicity.
jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
jlong soft_ref_clock = java_lang_ref_SoftReference::clock();
assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync");
@ -161,10 +166,11 @@ void ReferenceProcessor::update_soft_ref_master_clock() {
_soft_ref_timestamp_clock, now);
}
)
// In product mode, protect ourselves from system time being adjusted
// externally and going backward; see note in the implementation of
// GenCollectedHeap::time_since_last_gc() for the right way to fix
// this uniformly throughout the VM; see bug-id 4741166. XXX
// The values of now and _soft_ref_timestamp_clock are set using
// javaTimeNanos(), which is guaranteed to be monotonically
// non-decreasing provided the underlying platform provides such
// a time source (and it is bug free).
// In product mode, however, protect ourselves from non-monotonicty.
if (now > _soft_ref_timestamp_clock) {
_soft_ref_timestamp_clock = now;
java_lang_ref_SoftReference::set_clock(now);