# HG changeset patch
# User Haoyu Li <leihouyju@gmail.com>
# Date 1575363615 -28800
#      Tue Dec 03 17:00:15 2019 +0800
# Node ID fbd52e214fa2c9eaa5c66f8f63b69d83020e164e
# Parent  fa1262fd180c86883401cd90f6f7bd0b9a6483d9
use the ~0 sentinel, delete a line of dead code, and replace MutexLocker with MonitorLocker

diff -r fa1262fd180c -r fbd52e214fa2 src/hotspot/share/gc/parallel/psCompactionManager.cpp
--- a/src/hotspot/share/gc/parallel/psCompactionManager.cpp	Thu Nov 28 21:23:56 2019 +0800
+++ b/src/hotspot/share/gc/parallel/psCompactionManager.cpp	Tue Dec 03 17:00:15 2019 +0800
@@ -173,24 +173,25 @@
 }
 
 size_t ParCompactionManager::pop_shadow_region_mt_safe(PSParallelCompact::RegionData* region_ptr) {
+  MonitorLocker ml(_shadow_region_monitor, Mutex::_no_safepoint_check_flag);
   while (true) {
-    MutexLocker ml(_shadow_region_monitor, Mutex::_no_safepoint_check_flag);
-    if (_shadow_region_array->is_empty()) {
-      // Check if the corresponding heap region is available now.
-      // If so, we don't need to get a shadow region anymore,
-      // and we return 0 to indicate this case
-      if (region_ptr->claimed()) {
-        return 0;
-      }
-    } else {
+    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) {
-  MutexLocker ml(_shadow_region_monitor, Mutex::_no_safepoint_check_flag);
+  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) {
diff -r fa1262fd180c -r fbd52e214fa2 src/hotspot/share/gc/parallel/psCompactionManager.hpp
--- a/src/hotspot/share/gc/parallel/psCompactionManager.hpp	Thu Nov 28 21:23:56 2019 +0800
+++ b/src/hotspot/share/gc/parallel/psCompactionManager.hpp	Tue Dec 03 17:00:15 2019 +0800
@@ -119,6 +119,7 @@
   // marking stack and overflow stack directly.
 
  public:
+  static const size_t  InvalidShadow = ~0;
   static size_t  pop_shadow_region_mt_safe(PSParallelCompact::RegionData* region_ptr);
   static void    push_shadow_region_mt_safe(size_t shadow_region);
   static void    push_shadow_region(size_t shadow_region);
diff -r fa1262fd180c -r fbd52e214fa2 src/hotspot/share/gc/parallel/psParallelCompact.cpp
--- a/src/hotspot/share/gc/parallel/psParallelCompact.cpp	Thu Nov 28 21:23:56 2019 +0800
+++ b/src/hotspot/share/gc/parallel/psParallelCompact.cpp	Tue Dec 03 17:00:15 2019 +0800
@@ -3061,7 +3061,6 @@
 void PSParallelCompact::fill_region(ParCompactionManager* cm, MoveAndUpdateClosure& closure, size_t region_idx)
 {
   typedef ParMarkBitMap::IterationStatus IterationStatus;
-  const size_t RegionSize = ParallelCompactData::RegionSize;
   ParMarkBitMap* const bitmap = mark_bitmap();
   ParallelCompactData& sd = summary_data();
   RegionData* const region_ptr = sd.region(region_idx);
@@ -3173,10 +3172,10 @@
   ParallelCompactData& sd = summary_data();
   RegionData* const region_ptr = sd.region(region_idx);
   size_t shadow_region = cm->pop_shadow_region_mt_safe(region_ptr);
-  // The zero return value indicates the corresponding heap region is available,
+  // The InvalidShadow return value indicates the corresponding heap region is available,
   // so use MoveAndUpdateClosure to fill the normal region. Otherwise, use
   // MoveAndUpdateShadowClosure to fill the acquired shadow region.
-  if (shadow_region == 0) {
+  if (shadow_region == cm->InvalidShadow) {
     MoveAndUpdateClosure cl(mark_bitmap(), cm, region_idx);
     region_ptr->shadow_to_normal();
     return fill_region(cm, cl, region_idx);