--- old/src/hotspot/share/gc/parallel/psCompactionManager.cpp	2019-12-04 16:34:00.308310756 +0100
+++ new/src/hotspot/share/gc/parallel/psCompactionManager.cpp	2019-12-04 16:34:00.104309873 +0100
@@ -49,6 +49,8 @@
 ObjectStartArray*    ParCompactionManager::_start_array = NULL;
 ParMarkBitMap*       ParCompactionManager::_mark_bitmap = NULL;
 RegionTaskQueueSet*  ParCompactionManager::_region_array = NULL;
+GrowableArray<size_t >* ParCompactionManager::_shadow_region_array = NULL;
+Monitor*                ParCompactionManager::_shadow_region_monitor = NULL;
 
 ParCompactionManager::ParCompactionManager() :
     _action(CopyAndUpdate) {
@@ -99,6 +101,11 @@
     "Could not create ParCompactionManager");
   assert(ParallelScavengeHeap::heap()->workers().total_workers() != 0,
     "Not initialized?");
+
+  _shadow_region_array = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<size_t >(10, true);
+
+  _shadow_region_monitor = new Monitor(Mutex::barrier, "CompactionManager monitor",
+                                       Mutex::_allow_vm_block_flag, Monitor::_safepoint_check_never);
 }
 
 void ParCompactionManager::reset_all_bitmap_query_caches() {
@@ -163,3 +170,33 @@
     }
   } while (!region_stack()->is_empty());
 }
+
+size_t ParCompactionManager::pop_shadow_region_mt_safe(PSParallelCompact::RegionData* region_ptr) {
+  MonitorLocker ml(_shadow_region_monitor, Mutex::_no_safepoint_check_flag);
+  while (true) {
+    if (!_shadow_region_array->is_empty()) {
+      return _shadow_region_array->pop();
+    }
+    // Check if the corresponding heap region is available now.
+    // If so, we don't need to get a shadow region anymore, and
+    // we return InvalidShadow to indicate such a case.
+    if (region_ptr->claimed()) {
+      return InvalidShadow;
+    }
+    ml.wait(1);
+  }
+}
+
+void ParCompactionManager::push_shadow_region_mt_safe(size_t shadow_region) {
+  MonitorLocker ml(_shadow_region_monitor, Mutex::_no_safepoint_check_flag);
+  _shadow_region_array->push(shadow_region);
+  ml.notify();
+}
+
+void ParCompactionManager::push_shadow_region(size_t shadow_region) {
+  _shadow_region_array->push(shadow_region);
+}
+
+void ParCompactionManager::remove_all_shadow_regions() {
+  _shadow_region_array->clear();
+}
\ No newline at end of file