8345970: pthread_getcpuclockid related crashes in shenandoah tests

Reviewed-by: shade
Backport-of: 2ce53e88481659734bc5424c643c5e31c116bc5d

src/hotspot/share/gc/shenandoah/shenandoahGenerationalHeap.cpp

@@ -180,8 +180,8 @@ void ShenandoahGenerationalHeap::gc_threads_do(ThreadClosure* tcl) const {
 }
 
 void ShenandoahGenerationalHeap::stop() {
-  regulator_thread()->stop();
   ShenandoahHeap::stop();
+  regulator_thread()->stop();
 }
 
 void ShenandoahGenerationalHeap::evacuate_collection_set(bool concurrent) {

src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp

@@ -538,7 +538,6 @@ ShenandoahHeap::ShenandoahHeap(ShenandoahCollectorPolicy* policy) :
   _pacer(nullptr),
   _verifier(nullptr),
   _phase_timings(nullptr),
-  _mmu_tracker(),
   _monitoring_support(nullptr),
   _memory_pool(nullptr),
   _stw_memory_manager("Shenandoah Pauses"),
@@ -632,6 +631,8 @@ public:
 
 void ShenandoahHeap::post_initialize() {
   CollectedHeap::post_initialize();
+
+  // Schedule periodic task to report on gc thread CPU utilization
   _mmu_tracker.initialize();
 
   MutexLocker ml(Threads_lock);
@@ -2084,6 +2085,9 @@ void ShenandoahHeap::stop() {
   // Step 0. Notify policy to disable event recording and prevent visiting gc threads during shutdown
   _shenandoah_policy->record_shutdown();
 
+  // Step 0a. Stop reporting on gc thread cpu utilization
+  mmu_tracker()->stop();
+
   // Step 1. Notify control thread that we are in shutdown.
   // Note that we cannot do that with stop(), because stop() is blocking and waits for the actual shutdown.
   // Doing stop() here would wait for the normal GC cycle to complete, never falling through to cancel below.

src/hotspot/share/gc/shenandoah/shenandoahMmuTracker.cpp

@@ -48,6 +48,7 @@ class ThreadTimeAccumulator : public ThreadClosure {
   size_t total_time;
   ThreadTimeAccumulator() : total_time(0) {}
   void do_thread(Thread* thread) override {
+    assert(!thread->has_terminated(), "Cannot get cpu time for terminated thread: " UINTX_FORMAT, thread->osthread()->thread_id_for_printing());
     total_time += os::thread_cpu_time(thread);
   }
 };
@@ -65,7 +66,6 @@ ShenandoahMmuTracker::ShenandoahMmuTracker() :
 }
 
 ShenandoahMmuTracker::~ShenandoahMmuTracker() {
-  _mmu_periodic_task->disenroll();
   delete _mmu_periodic_task;
 }
 
@@ -175,6 +175,10 @@ void ShenandoahMmuTracker::report() {
   log_debug(gc)("Periodic Sample: GCU = %.3f%%, MU = %.3f%% during most recent %.1fs", gcu * 100, mu * 100, time_delta);
 }
 
+void ShenandoahMmuTracker::stop() const {
+  _mmu_periodic_task->disenroll();
+}
+
 void ShenandoahMmuTracker::initialize() {
   // initialize static data
   _active_processors = os::initial_active_processor_count();

src/hotspot/share/gc/shenandoah/shenandoahMmuTracker.hpp

@@ -101,6 +101,10 @@ public:
   // GCPauseIntervalMillis and defaults to 5 seconds. This method computes
   // the MMU over the elapsed interval and records it in a running average.
   void report();
+
+  // Unenrolls the periodic task that collects CPU utilization for GC threads. This must happen _before_ the
+  // gc threads are stopped and terminated.
+  void stop() const;
 };
 
 #endif //SHARE_GC_SHENANDOAH_SHENANDOAHMMUTRACKER_HPP