8221153: ZGC: Heap iteration and verification pollutes GC statistics

Reviewed-by: stefank, eosterlund

src/hotspot/share/gc/z/zHeap.cpp

@@ -540,16 +540,19 @@ void ZHeap::print_extended_on(outputStream* st) const {
 
 class ZVerifyRootsTask : public ZTask {
 private:
+  ZStatTimerDisable  _disable;
   ZRootsIterator     _strong_roots;
   ZWeakRootsIterator _weak_roots;
 
 public:
   ZVerifyRootsTask() :
       ZTask("ZVerifyRootsTask"),
+      _disable(),
       _strong_roots(),
       _weak_roots() {}
 
   virtual void work() {
+    ZStatTimerDisable disable;
     ZVerifyOopClosure cl;
     _strong_roots.oops_do(&cl);
     _weak_roots.oops_do(&cl);

src/hotspot/share/gc/z/zHeapIterator.cpp

@@ -28,6 +28,7 @@
 #include "gc/z/zHeapIterator.hpp"
 #include "gc/z/zOop.inline.hpp"
 #include "gc/z/zRootsIterator.hpp"
+#include "gc/z/zStat.hpp"
 #include "memory/iterator.inline.hpp"
 #include "utilities/bitMap.inline.hpp"
 #include "utilities/stack.inline.hpp"
@@ -170,6 +171,7 @@ void ZHeapIterator::objects_do(ObjectClosure* cl) {
   // If we didn't do this the application would have expected to see
   // ObjectFree events for phantom reachable objects in the tag map.
 
+  ZStatTimerDisable disable;
   ZHeapIteratorRootOopClosure root_cl(this);
 
   // Push strong roots onto stack

src/hotspot/share/gc/z/zStat.cpp

@@ -748,6 +748,11 @@ void ZStatCriticalPhase::register_end(const Ticks& start, const Ticks& end) cons
   }
 }
 
+//
+// Stat timer
+//
+__thread uint32_t ZStatTimerDisable::_active = 0;
+
 //
 // Stat sample/inc
 //

src/hotspot/share/gc/z/zStat.hpp

@@ -269,21 +269,45 @@ public:
 //
 // Stat timer
 //
+class ZStatTimerDisable : public StackObj {
+private:
+  static __thread uint32_t _active;
+
+public:
+  ZStatTimerDisable() {
+    _active++;
+  }
+
+  ~ZStatTimerDisable() {
+    _active--;
+  }
+
+  static bool is_active() {
+    return _active > 0;
+  }
+};
+
 class ZStatTimer : public StackObj {
 private:
+  const bool        _enabled;
   const ZStatPhase& _phase;
   const Ticks       _start;
 
 public:
   ZStatTimer(const ZStatPhase& phase) :
+      _enabled(!ZStatTimerDisable::is_active()),
       _phase(phase),
       _start(Ticks::now()) {
-    _phase.register_start(_start);
+    if (_enabled) {
+      _phase.register_start(_start);
+    }
   }
 
   ~ZStatTimer() {
-    const Ticks end = Ticks::now();
-    _phase.register_end(_start, end);
+    if (_enabled) {
+      const Ticks end = Ticks::now();
+      _phase.register_end(_start, end);
+    }
   }
 };