--- a/src/hotspot/share/gc/shared/memAllocator.cpp	Wed Oct 03 23:00:32 2018 -0700
+++ b/src/hotspot/share/gc/shared/memAllocator.cpp	Mon Oct 15 14:16:35 2018 -0700
@@ -187,7 +187,7 @@
   // support for JVMTI VMObjectAlloc event (no-op if not enabled)
   JvmtiExport::vm_object_alloc_event_collector(obj());
 
-  if (!ThreadHeapSampler::enabled()) {
+  if (!JvmtiExport::should_post_sampled_object_alloc()) {
     // Sampling disabled
     return;
   }
@@ -282,7 +282,7 @@
   HeapWord* mem = NULL;
   ThreadLocalAllocBuffer& tlab = _thread->tlab();
 
-  if (ThreadHeapSampler::enabled()) {
+  if (JvmtiExport::should_post_sampled_object_alloc()) {
     // Try to allocate the sampled object from TLAB, it is possible a sample
     // point was put and the TLAB still has space.
     tlab.set_back_allocation_end();

--- a/src/hotspot/share/prims/jvmtiEnv.cpp	Wed Oct 03 23:00:32 2018 -0700
+++ b/src/hotspot/share/prims/jvmtiEnv.cpp	Mon Oct 15 14:16:35 2018 -0700
@@ -540,13 +540,6 @@
       record_class_file_load_hook_enabled();
     }
 
-    if (event_type == JVMTI_EVENT_SAMPLED_OBJECT_ALLOC) {
-      if (enabled) {
-        ThreadHeapSampler::enable();
-      } else {
-        ThreadHeapSampler::disable();
-      }
-    }
     JvmtiEventController::set_user_enabled(this, (JavaThread*) NULL, event_type, enabled);
   } else {
     // We have a specified event_thread.

--- a/src/hotspot/share/runtime/mutexLocker.cpp	Wed Oct 03 23:00:32 2018 -0700
+++ b/src/hotspot/share/runtime/mutexLocker.cpp	Mon Oct 15 14:16:35 2018 -0700
@@ -133,8 +133,6 @@
 Monitor* PeriodicTask_lock            = NULL;
 Monitor* RedefineClasses_lock         = NULL;
 
-Mutex*   ThreadHeapSampler_lock       = NULL;
-
 #if INCLUDE_JFR
 Mutex*   JfrStacktrace_lock           = NULL;
 Monitor* JfrMsg_lock                  = NULL;
@@ -301,8 +299,6 @@
   def(PeriodicTask_lock            , PaddedMonitor, nonleaf+5,   true,  Monitor::_safepoint_check_sometimes);
   def(RedefineClasses_lock         , PaddedMonitor, nonleaf+5,   true,  Monitor::_safepoint_check_always);
 
-  def(ThreadHeapSampler_lock       , PaddedMutex,   nonleaf,     false, Monitor::_safepoint_check_never);
-
   if (WhiteBoxAPI) {
     def(Compilation_lock           , PaddedMonitor, leaf,        false, Monitor::_safepoint_check_never);
   }

--- a/src/hotspot/share/runtime/mutexLocker.hpp	Wed Oct 03 23:00:32 2018 -0700
+++ b/src/hotspot/share/runtime/mutexLocker.hpp	Mon Oct 15 14:16:35 2018 -0700
@@ -132,7 +132,6 @@
 extern Monitor* Service_lock;                    // a lock used for service thread operation
 extern Monitor* PeriodicTask_lock;               // protects the periodic task structure
 extern Monitor* RedefineClasses_lock;            // locks classes from parallel redefinition
-extern Mutex*   ThreadHeapSampler_lock;          // protects the static data for initialization.
 
 #if INCLUDE_JFR
 extern Mutex*   JfrStacktrace_lock;              // used to guard access to the JFR stacktrace table

--- a/src/hotspot/share/runtime/threadHeapSampler.cpp	Wed Oct 03 23:00:32 2018 -0700
+++ b/src/hotspot/share/runtime/threadHeapSampler.cpp	Mon Oct 15 14:16:35 2018 -0700
@@ -29,22 +29,29 @@
 #include "runtime/sharedRuntime.hpp"
 #include "runtime/threadHeapSampler.hpp"
 
-// Cheap random number generator
+// Cheap random number generator.
 uint64_t ThreadHeapSampler::_rnd;
 // Default is 512kb.
-int ThreadHeapSampler::_sampling_interval = 512 * 1024;
-int ThreadHeapSampler::_enabled;
+volatile int ThreadHeapSampler::_sampling_interval = 512 * 1024;
+
+// Ordering here is important: _log_table first, _log_table_initialized second.
+double ThreadHeapSampler::_log_table[1 << ThreadHeapSampler::FastLogNumBits] = {};
+
+// Force initialization of the log_table.
+bool ThreadHeapSampler::_log_table_initialized = init_log_table();
 
-// Statics for the fast log
-static const int FastLogNumBits = 10;
-static const int FastLogMask = (1 << FastLogNumBits) - 1;
-static double log_table[1<<FastLogNumBits];  // Constant
-static bool log_table_initialized;
+bool ThreadHeapSampler::init_log_table() {
+  for (int i = 0; i < (1 << FastLogNumBits); i++) {
+    _log_table[i] = (log(1.0 + static_cast<double>(i+0.5) / (1 << FastLogNumBits))
+                    / log(2.0));
+  }
+  return true;
+}
 
 // Returns the next prng value.
 // pRNG is: aX+b mod c with a = 0x5DEECE66D, b =  0xB, c = 1<<48
 // This is the lrand64 generator.
-static uint64_t next_random(uint64_t rnd) {
+uint64_t ThreadHeapSampler::next_random(uint64_t rnd) {
   const uint64_t PrngMult = 0x5DEECE66DLL;
   const uint64_t PrngAdd = 0xB;
   const uint64_t PrngModPower = 48;
@@ -54,7 +61,7 @@
   return (PrngMult * rnd + PrngAdd) & PrngModMask;
 }
 
-static double fast_log2(const double & d) {
+double ThreadHeapSampler::fast_log2(const double& d) {
   assert(d>0, "bad value passed to assert");
   uint64_t x = 0;
   assert(sizeof(d) == sizeof(x),
@@ -64,7 +71,9 @@
   assert(FastLogNumBits <= 20, "FastLogNumBits should be less than 20.");
   const uint32_t y = x_high >> (20 - FastLogNumBits) & FastLogMask;
   const int32_t exponent = ((x_high >> 20) & 0x7FF) - 1023;
-  return exponent + log_table[y];
+
+  assert(_log_table_initialized, "log table should be initialized");
+  return exponent + _log_table[y];
 }
 
 // Generates a geometric variable with the specified mean (512K by default).
@@ -134,36 +143,6 @@
   pick_next_sample(overflow_bytes);
 }
 
-void ThreadHeapSampler::init_log_table() {
-  MutexLockerEx mu(ThreadHeapSampler_lock, Mutex::_no_safepoint_check_flag);
-
-  if (log_table_initialized) {
-    return;
-  }
-
-  for (int i = 0; i < (1 << FastLogNumBits); i++) {
-    log_table[i] = (log(1.0 + static_cast<double>(i+0.5) / (1 << FastLogNumBits))
-                    / log(2.0));
-  }
-
-  log_table_initialized = true;
-}
-
-void ThreadHeapSampler::enable() {
-  // Done here to be done when things have settled. This adds a mutex lock but
-  // presumably, users won't be enabling and disabling all the time.
-  init_log_table();
-  OrderAccess::release_store(&_enabled, 1);
-}
-
-int ThreadHeapSampler::enabled() {
-  return OrderAccess::load_acquire(&_enabled);
-}
-
-void ThreadHeapSampler::disable() {
-  OrderAccess::release_store(&_enabled, 0);
-}
-
 int ThreadHeapSampler::get_sampling_interval() {
   return OrderAccess::load_acquire(&_sampling_interval);
 }

--- a/src/hotspot/share/runtime/threadHeapSampler.hpp	Wed Oct 03 23:00:32 2018 -0700
+++ b/src/hotspot/share/runtime/threadHeapSampler.hpp	Mon Oct 15 14:16:35 2018 -0700
@@ -30,16 +30,24 @@
 
 class ThreadHeapSampler {
  private:
+  // Statics for the fast log
+  static const int FastLogNumBits = 10;
+  static const int FastLogMask = (1 << FastLogNumBits) - 1;
+
   size_t _bytes_until_sample;
   // Cheap random number generator
   static uint64_t _rnd;
+  static bool _log_table_initialized;
+
+  static double _log_table[1<<FastLogNumBits];  // Constant
+  static volatile int _sampling_interval;
 
   void pick_next_geometric_sample();
   void pick_next_sample(size_t overflowed_bytes = 0);
-  static int _enabled;
-  static int _sampling_interval;
 
-  static void init_log_table();
+  static double fast_log2(const double& d);
+  static bool init_log_table();
+  uint64_t next_random(uint64_t rnd);
 
  public:
   ThreadHeapSampler() : _bytes_until_sample(0) {
@@ -54,10 +62,6 @@
 
   void check_for_sampling(oop obj, size_t size_in_bytes, size_t bytes_allocated_before);
 
-  static int enabled();
-  static void enable();
-  static void disable();
-
   static void set_sampling_interval(int sampling_interval);
   static int get_sampling_interval();
 };