8252476: as_Worker_thread() doesn't check what it intends

Co-authored-by: David Holmes <dholmes@openjdk.org>
Reviewed-by: iklam, kbarrett

Author: albertnetymk

src/hotspot/share/gc/shared/referenceProcessor.cpp

@@ -40,6 +40,7 @@
 #include "oops/oop.inline.hpp"
 #include "runtime/java.hpp"
 #include "runtime/nonJavaThread.hpp"
+#include "runtime/thread.inline.hpp"
 
 ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL;
 ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy      = NULL;

src/hotspot/share/runtime/nonJavaThread.hpp

@@ -106,11 +106,6 @@ class WorkerThread: public NamedThread {
   WorkerThread() : _id(0)               { }
   virtual bool is_Worker_thread() const { return true; }
 
-  virtual WorkerThread* as_Worker_thread() const {
-    assert(is_Worker_thread(), "Dubious cast to WorkerThread*?");
-    return (WorkerThread*) this;
-  }
-
   void set_id(uint work_id)             { _id = work_id; }
   uint id() const                       { return _id; }
 };

src/hotspot/share/runtime/thread.hpp

@@ -355,7 +355,7 @@ class Thread: public ThreadShadow {
   virtual bool is_active_Java_thread() const         { return false; }
 
   // Casts
-  virtual WorkerThread* as_Worker_thread() const     { return NULL; }
+  inline const WorkerThread* as_Worker_thread() const;
   inline JavaThread* as_Java_thread();
   inline const JavaThread* as_Java_thread() const;
 

src/hotspot/share/runtime/thread.inline.hpp

@@ -31,6 +31,7 @@
 #include "runtime/orderAccess.hpp"
 #include "runtime/safepoint.hpp"
 #include "runtime/thread.hpp"
+#include "runtime/nonJavaThread.hpp"
 
 #if defined(__APPLE__) && defined(AARCH64)
 #include "runtime/os.hpp"
@@ -64,6 +65,11 @@ inline void Thread::set_threads_hazard_ptr(ThreadsList* new_list) {
   Atomic::release_store_fence(&_threads_hazard_ptr, new_list);
 }
 
+inline const WorkerThread* Thread::as_Worker_thread() const {
+  assert(is_Worker_thread(), "incorrect cast to const WorkerThread");
+  return static_cast<const WorkerThread*>(this);
+}
+
 #if defined(__APPLE__) && defined(AARCH64)
 inline void Thread::init_wx() {
   assert(this == Thread::current(), "should only be called for current thread");