From 90f087b84d3a7e129bb2ed9af31397caa5518af3 Mon Sep 17 00:00:00 2001
From: Yi Lin <qinsoon@gmail.com>
Date: Fri, 15 Aug 2025 04:21:57 +0000
Subject: [PATCH] Acquire and release heap lock on VM_MMTkSTWOperation

---
 openjdk/mmtkUpcalls.cpp     | 12 ------------
 openjdk/mmtkVMOperation.cpp | 13 +++++++++++++
 openjdk/mmtkVMOperation.hpp |  2 ++
 3 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/openjdk/mmtkUpcalls.cpp b/openjdk/mmtkUpcalls.cpp
index c665a191..fd90cf0e 100644
--- a/openjdk/mmtkUpcalls.cpp
+++ b/openjdk/mmtkUpcalls.cpp
@@ -87,15 +87,6 @@ static void mmtk_resume_mutators(void *tls) {
     MutexLockerEx locker(MMTkHeap::heap()->gc_lock(), Mutex::_no_safepoint_check_flag);
     MMTkHeap::heap()->gc_lock()->notify_all();
   }
-
-  log_debug(gc)("Notifying mutators blocking on Heap_lock for reference pending list...");
-  // Note: That's the ReferenceHandler thread.
-  {
-    MutexLockerEx x(Heap_lock, Mutex::_no_safepoint_check_flag);
-    if (Universe::has_reference_pending_list()) {
-      Heap_lock->notify_all();
-    }
-  }
 }
 
 static const int GC_THREAD_KIND_WORKER = 1;
@@ -302,8 +293,6 @@ static void mmtk_enqueue_references(void** objects, size_t len) {
     return;
   }
 
-  MutexLocker x(Heap_lock);
-
   oop first = (oop) objects[0]; // This points to the first node of the linked list.
   oop last = first; // This points to the last node of the linked list.
 
@@ -324,7 +313,6 @@ static void mmtk_enqueue_references(void** objects, size_t len) {
 
   oop old_first = Universe::swap_reference_pending_list(first);
   HeapAccess<AS_NO_KEEPALIVE>::oop_store_at(last, java_lang_ref_Reference::discovered_offset, old_first);
-  assert(Universe::has_reference_pending_list(), "Reference pending list is empty after swap");
 }
 
 OpenJDK_Upcalls mmtk_upcalls = {
diff --git a/openjdk/mmtkVMOperation.cpp b/openjdk/mmtkVMOperation.cpp
index 51227ee3..7ba6053f 100644
--- a/openjdk/mmtkVMOperation.cpp
+++ b/openjdk/mmtkVMOperation.cpp
@@ -32,8 +32,21 @@ VM_MMTkSTWOperation::VM_MMTkSTWOperation(MMTkVMCompanionThread *companion_thread
     _companion_thread(companion_thread) {
 }
 
+bool VM_MMTkSTWOperation::doit_prologue() {
+    Heap_lock->lock();
+    return true;
+}
+
 void VM_MMTkSTWOperation::doit() {
     log_trace(vmthread)("Entered VM_MMTkSTWOperation::doit().");
     _companion_thread->do_mmtk_stw_operation();
     log_trace(vmthread)("Leaving VM_MMTkSTWOperation::doit()");
 }
+
+void VM_MMTkSTWOperation::doit_epilogue() {
+    // Notify the reference processing thread
+    if (Universe::has_reference_pending_list()) {
+        Heap_lock->notify_all();
+    }
+    Heap_lock->unlock();
+}
diff --git a/openjdk/mmtkVMOperation.hpp b/openjdk/mmtkVMOperation.hpp
index 98d37ea4..49897ce7 100644
--- a/openjdk/mmtkVMOperation.hpp
+++ b/openjdk/mmtkVMOperation.hpp
@@ -39,7 +39,9 @@ class VM_MMTkSTWOperation : public VM_MMTkOperation {
 
 public:
   VM_MMTkSTWOperation(MMTkVMCompanionThread *companion_thread);
+  virtual bool doit_prologue() override;
   virtual void doit() override;
+  virtual void doit_epilogue() override;
 };
 
 #endif // MMTK_OPENJDK_MMTK_VM_OPERATION_HPP