--- old/src/hotspot/share/prims/jvm.cpp	2019-10-17 17:28:51.000000000 -0400
+++ new/src/hotspot/share/prims/jvm.cpp	2019-10-17 17:28:50.000000000 -0400
@@ -73,6 +73,7 @@
 #include "runtime/os.inline.hpp"
 #include "runtime/perfData.hpp"
 #include "runtime/reflection.hpp"
+#include "runtime/synchronizer.hpp"
 #include "runtime/thread.inline.hpp"
 #include "runtime/threadSMR.hpp"
 #include "runtime/vframe.inline.hpp"
@@ -484,6 +485,11 @@
 JVM_ENTRY_NO_ENV(void, JVM_GC(void))
   JVMWrapper("JVM_GC");
   if (!DisableExplicitGC) {
+    if (AsyncDeflateIdleMonitors) {
+      // AsyncDeflateIdleMonitors needs to know when System.gc() is
+      // called so any special deflation can be done at a safepoint.
+      ObjectSynchronizer::set_is_special_deflation_requested(true);
+    }
     Universe::heap()->collect(GCCause::_java_lang_system_gc);
   }
 JVM_END