--- old/src/hotspot/share/gc/shenandoah/shenandoahRootProcessor.cpp	2020-05-28 21:49:27.242475720 +0200
+++ new/src/hotspot/share/gc/shenandoah/shenandoahRootProcessor.cpp	2020-05-28 21:49:26.926474898 +0200
@@ -223,17 +223,20 @@
           "Expect class unloading when Shenandoah cycle is running");
   ResourceMark rm;
 
-  _serial_roots.oops_do(oops, worker_id);
-  _vm_roots.oops_do(oops, worker_id);
-
   assert(clds != NULL, "Only possible with CLD closure");
-  _cld_roots.cld_do(clds, worker_id);
 
-  ShenandoahParallelOopsDoThreadClosure tc_cl(oops, code, tc);
-  _thread_roots.threads_do(&tc_cl, worker_id);
+  // Process serial-claiming roots first
+  _serial_roots.oops_do(oops, worker_id);
+  _cld_roots.cld_do(clds, worker_id);
 
+   // Process light-weight parallel roots then
+  _vm_roots.oops_do(oops, worker_id);
   AlwaysTrueClosure always_true;
   _dedup_roots.oops_do(&always_true, oops, worker_id);
+
+  // Process heavy-weight parallel roots the last
+  ShenandoahParallelOopsDoThreadClosure tc_cl(oops, code, tc);
+  _thread_roots.threads_do(&tc_cl, worker_id);
 }
 
 void ShenandoahRootScanner::strong_roots_do(uint worker_id, OopClosure* oops, CLDClosure* clds, CodeBlobClosure* code, ThreadClosure* tc) {
@@ -241,9 +244,14 @@
   ShenandoahParallelOopsDoThreadClosure tc_cl(oops, code, tc);
   ResourceMark rm;
 
+  // Process serial-claiming roots first
   _serial_roots.oops_do(oops, worker_id);
-  _vm_roots.oops_do(oops, worker_id);
   _cld_roots.always_strong_cld_do(clds, worker_id);
+
+  // Process light-weight parallel roots then
+  _vm_roots.oops_do(oops, worker_id);
+
+  // Process heavy-weight parallel roots the last
   _thread_roots.threads_do(&tc_cl, worker_id);
 }
 
@@ -272,17 +280,23 @@
                                    static_cast<CodeBlobToOopClosure*>(&blobsCl);
   AlwaysTrueClosure always_true;
 
+  // Process serial-claiming roots first
   _serial_roots.oops_do(oops, worker_id);
   _serial_weak_roots.weak_oops_do(oops, worker_id);
+  if (_stw_class_unloading) {
+    CLDToOopClosure clds(oops, ClassLoaderData::_claim_strong);
+    _cld_roots.cld_do(&clds, worker_id);
+  }
+
+  // Process light-weight parallel roots then
   if (_stw_roots_processing) {
     _vm_roots.oops_do<OopClosure>(oops, worker_id);
     _weak_roots.oops_do<OopClosure>(oops, worker_id);
     _dedup_roots.oops_do(&always_true, oops, worker_id);
   }
 
+  // Process heavy-weight parallel roots the last
   if (_stw_class_unloading) {
-    CLDToOopClosure clds(oops, ClassLoaderData::_claim_strong);
-    _cld_roots.cld_do(&clds, worker_id);
     _code_roots.code_blobs_do(codes_cl, worker_id);
     _thread_roots.oops_do(oops, NULL, worker_id);
   } else {
@@ -324,16 +338,19 @@
   CLDToOopClosure adjust_cld_closure(oops, ClassLoaderData::_claim_strong);
   AlwaysTrueClosure always_true;
 
+  // Process serial-claiming roots first
   _serial_roots.oops_do(oops, worker_id);
-  _vm_roots.oops_do(oops, worker_id);
-
-  _thread_roots.oops_do(oops, NULL, worker_id);
+  _serial_weak_roots.weak_oops_do(oops, worker_id);
   _cld_roots.cld_do(&adjust_cld_closure, worker_id);
-  _code_roots.code_blobs_do(adjust_code_closure, worker_id);
 
-  _serial_weak_roots.weak_oops_do(oops, worker_id);
+  // Process light-weight parallel roots then
+  _vm_roots.oops_do(oops, worker_id);
   _weak_roots.oops_do<OopClosure>(oops, worker_id);
   _dedup_roots.oops_do(&always_true, oops, worker_id);
+
+  // Process heavy-weight parallel roots the last
+  _code_roots.code_blobs_do(adjust_code_closure, worker_id);
+  _thread_roots.oops_do(oops, NULL, worker_id);
 }
 
 ShenandoahHeapIterationRootScanner::ShenandoahHeapIterationRootScanner() :
@@ -356,13 +373,17 @@
    AlwaysTrueClosure always_true;
    ResourceMark rm;
 
+   // Process serial-claiming roots first
    _serial_roots.oops_do(oops, 0);
-   _vm_roots.oops_do(oops, 0);
+   _serial_weak_roots.weak_oops_do(oops, 0);
    _cld_roots.cld_do(&clds, 0);
-   _thread_roots.threads_do(&tc_cl, 0);
-   _code_roots.code_blobs_do(&code, 0);
 
-   _serial_weak_roots.weak_oops_do(oops, 0);
+   // Process light-weight parallel roots then
+   _vm_roots.oops_do(oops, 0);
    _weak_roots.oops_do<OopClosure>(oops, 0);
    _dedup_roots.oops_do(&always_true, oops, 0);
+
+   // Process heavy-weight parallel roots the last
+   _code_roots.code_blobs_do(&code, 0);
+   _thread_roots.threads_do(&tc_cl, 0);
  }