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8369447: GenShen: Regulator thread may observe inconsistent states #500

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8369447: GenShen: Regulator thread may observe inconsistent states #500

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96d616e
Backport 926f61f2e358c92cdb7ccdf75c853aa599f4dde3
Oct 17, 2025
6c996a7
Merge remote-tracking branch 'jdk25u-dev/master' into backport-JDK-83…
earthling-amzn May 6, 2026
61e3477
Bring in a fix mixed into a more complicated change
earthling-amzn May 6, 2026
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10 changes: 10 additions & 0 deletions src/hotspot/share/gc/shenandoah/shenandoahRegulatorThread.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,7 @@ void ShenandoahRegulatorThread::run_service() {

void ShenandoahRegulatorThread::regulate_young_and_old_cycles() {
while (!should_terminate()) {
SuspendibleThreadSetJoiner joiner;
ShenandoahGenerationalControlThread::GCMode mode = _control_thread->gc_mode();
if (mode == ShenandoahGenerationalControlThread::none) {
if (should_start_metaspace_gc()) {
Expand Down Expand Up @@ -95,6 +96,7 @@ void ShenandoahRegulatorThread::regulate_young_and_old_cycles() {

void ShenandoahRegulatorThread::regulate_young_and_global_cycles() {
while (!should_terminate()) {
SuspendibleThreadSetJoiner joiner;
if (_control_thread->gc_mode() == ShenandoahGenerationalControlThread::none) {
if (start_global_cycle()) {
log_debug(gc)("Heuristics request for global collection accepted.");
Expand Down Expand Up @@ -122,6 +124,7 @@ void ShenandoahRegulatorThread::regulator_sleep() {
_last_sleep_adjust_time = current;
}

SuspendibleThreadSetLeaver leaver;
os::naked_short_sleep(_sleep);
if (LogTarget(Debug, gc, thread)::is_enabled()) {
double elapsed = os::elapsedTime() - current;
Expand All @@ -146,6 +149,13 @@ bool ShenandoahRegulatorThread::start_global_cycle() const {

bool ShenandoahRegulatorThread::request_concurrent_gc(ShenandoahGeneration* generation) const {
double now = os::elapsedTime();

// This call may find the control thread waiting on workers which have suspended
// to allow a safepoint to run. If this regulator thread does not yield, the safepoint
// will not run. The worker threads won't progress, the control thread won't progress,
// and the regulator thread may never yield. Therefore, we leave the suspendible
// thread set before making this call.
SuspendibleThreadSetLeaver leaver;
bool accepted = _control_thread->request_concurrent_gc(generation);
if (LogTarget(Debug, gc, thread)::is_enabled() && accepted) {
double wait_time = os::elapsedTime() - now;
Expand Down