--- a/src/hotspot/share/jfr/leakprofiler/checkpoint/eventEmitter.cpp	Wed Oct 30 16:14:56 2019 +0100
+++ b/src/hotspot/share/jfr/leakprofiler/checkpoint/eventEmitter.cpp	Wed Oct 30 19:43:52 2019 +0100
@@ -34,6 +34,7 @@
 #include "memory/resourceArea.hpp"
 #include "oops/markWord.hpp"
 #include "oops/oop.inline.hpp"
+#include "runtime/mutexLocker.hpp"
 #include "runtime/thread.inline.hpp"
 #include "runtime/vmThread.hpp"
 
@@ -51,8 +52,8 @@
 }
 
 void EventEmitter::emit(ObjectSampler* sampler, int64_t cutoff_ticks, bool emit_all) {
+  assert(JfrStream_lock->owned_by_self(), "invariant");
   assert(sampler != NULL, "invariant");
-
   ResourceMark rm;
   EdgeStore edge_store;
   if (cutoff_ticks <= 0) {
@@ -68,6 +69,7 @@
 }
 
 size_t EventEmitter::write_events(ObjectSampler* object_sampler, EdgeStore* edge_store, bool emit_all) {
+  assert_locked_or_safepoint(JfrStream_lock);
   assert(_thread == Thread::current(), "invariant");
   assert(_thread->jfr_thread_local() == _jfr_thread_local, "invariant");
   assert(object_sampler != NULL, "invariant");