--- a/src/hotspot/share/jfr/leakprofiler/checkpoint/objectSampleCheckpoint.cpp	Sat Oct 26 23:59:51 2019 +0200
+++ b/src/hotspot/share/jfr/leakprofiler/checkpoint/objectSampleCheckpoint.cpp	Mon Oct 28 18:43:04 2019 +0100
@@ -37,6 +37,7 @@
 #include "jfr/recorder/stacktrace/jfrStackTraceRepository.hpp"
 #include "jfr/utilities/jfrHashtable.hpp"
 #include "jfr/utilities/jfrTypes.hpp"
+#include "runtime/mutexLocker.hpp"
 #include "runtime/safepoint.hpp"
 #include "runtime/thread.hpp"
 #include "utilities/growableArray.hpp"
@@ -291,6 +292,7 @@
 
 // caller needs ResourceMark
 void ObjectSampleCheckpoint::on_rotation(const ObjectSampler* sampler, JfrStackTraceRepository& stack_trace_repo) {
+  assert(JfrStream_lock->owned_by_self(), "invariant");
   assert(sampler != NULL, "invariant");
   assert(LeakProfiler::is_running(), "invariant");
   install_stack_traces(sampler, stack_trace_repo);
@@ -397,6 +399,7 @@
 }
 
 void ObjectSampleCheckpoint::write(const ObjectSampler* sampler, EdgeStore* edge_store, bool emit_all, Thread* thread) {
+  assert_locked_or_safepoint(JfrStream_lock);
   assert(sampler != NULL, "invariant");
   assert(edge_store != NULL, "invariant");
   assert(thread != NULL, "invariant");