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7098282: G1: assert(interval >= 0) failed: Sanity check, referencePolicy.cpp: 76

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There is a race between one thread successfully forwarding and copying the klass mirror for the SoftReference class (including the static master clock) and another thread attempting to use the master clock while attempting to discover a soft reference object. Maintain a shadow copy of the soft reference master clock and use the shadow during reference discovery and reference processing.

Reviewed-by: tonyp, brutisso, ysr
This commit is contained in:
John Cuthbertson 2011-10-12 10:25:51 -07:00
parent 7fa7f8a597
commit 4738ed88a5
4 changed files with 75 additions and 33 deletions
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58
hotspot/src/share/vm/memory/referenceProcessor.cpp
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@ -36,14 +36,19 @@
ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL;
ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL;
bool ReferenceProcessor::_pending_list_uses_discovered_field = false;
jlong ReferenceProcessor::_soft_ref_timestamp_clock = 0;
void referenceProcessor_init() {
ReferenceProcessor::init_statics();
}
void ReferenceProcessor::init_statics() {
// Initialize the master soft ref clock.
java_lang_ref_SoftReference::set_clock(os::javaTimeMillis());
jlong now = os::javaTimeMillis();
// Initialize the soft ref timestamp clock.
_soft_ref_timestamp_clock = now;
// Also update the soft ref clock in j.l.r.SoftReference
java_lang_ref_SoftReference::set_clock(_soft_ref_timestamp_clock);
_always_clear_soft_ref_policy = new AlwaysClearPolicy();
_default_soft_ref_policy = new COMPILER2_PRESENT(LRUMaxHeapPolicy())
@ -57,6 +62,28 @@ void ReferenceProcessor::init_statics() {
_pending_list_uses_discovered_field = JDK_Version::current().pending_list_uses_discovered_field();
}
void ReferenceProcessor::enable_discovery(bool verify_disabled, bool check_no_refs) {
#ifdef ASSERT
// Verify that we're not currently discovering refs
assert(!verify_disabled || !_discovering_refs, "nested call?");
if (check_no_refs) {
// Verify that the discovered lists are empty
verify_no_references_recorded();
}
#endif // ASSERT
// Someone could have modified the value of the static
// field in the j.l.r.SoftReference class that holds the
// soft reference timestamp clock using reflection or
// Unsafe between GCs. Unconditionally update the static
// field in ReferenceProcessor here so that we use the new
// value during reference discovery.
_soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
_discovering_refs = true;
}
ReferenceProcessor::ReferenceProcessor(MemRegion span,
bool mt_processing,
int mt_processing_degree,
@ -122,17 +149,21 @@ 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();
jlong clock = java_lang_ref_SoftReference::clock();
jlong soft_ref_clock = java_lang_ref_SoftReference::clock();
assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync");
NOT_PRODUCT(
if (now < clock) {
warning("time warp: %d to %d", clock, now);
if (now < _soft_ref_timestamp_clock) {
warning("time warp: "INT64_FORMAT" to "INT64_FORMAT,
_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
if (now > clock) {
if (now > _soft_ref_timestamp_clock) {
_soft_ref_timestamp_clock = now;
java_lang_ref_SoftReference::set_clock(now);
}
// Else leave clock stalled at its old value until time progresses
@ -150,6 +181,16 @@ void ReferenceProcessor::process_discovered_references(
// Stop treating discovered references specially.
disable_discovery();
// If discovery was concurrent, someone could have modified
// the value of the static field in the j.l.r.SoftReference
// class that holds the soft reference timestamp clock using
// reflection or Unsafe between when discovery was enabled and
// now. Unconditionally update the static field in ReferenceProcessor
// here so that we use the new value during processing of the
// discovered soft refs.
_soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
bool trace_time = PrintGCDetails && PrintReferenceGC;
// Soft references
{
@ -486,7 +527,8 @@ ReferenceProcessor::process_phase1(DiscoveredList& refs_list,
while (iter.has_next()) {
iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive();
if (referent_is_dead && !policy->should_clear_reference(iter.obj())) {
if (referent_is_dead &&
!policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) {
if (TraceReferenceGC) {
gclog_or_tty->print_cr("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy",
iter.obj(), iter.obj()->blueprint()->internal_name());
@ -1117,7 +1159,7 @@ bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) {
// time-stamp policies advance the soft-ref clock only
// at a major collection cycle, this is always currently
// accurate.
if (!_current_soft_ref_policy->should_clear_reference(obj)) {
if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) {
return false;
}
}