src/java.base/share/classes/java/lang/ref/Finalizer.java

8197812: (ref) Data race in Finalizer
Reviewed-by: plevart, mchung

*** 34,103 ****
  final class Finalizer extends FinalReference<Object> { /* Package-private; must be in
                                                            same package as the Reference
                                                            class */
  
      private static ReferenceQueue<Object> queue = new ReferenceQueue<>();
      private static Finalizer unfinalized = null;
      private static final Object lock = new Object();
  
!     private Finalizer
!         next = null,
!         prev = null;
  
!     private boolean hasBeenFinalized() {
!         return (next == this);
!     }
! 
!     private void add() {
          synchronized (lock) {
              if (unfinalized != null) {
                  this.next = unfinalized;
                  unfinalized.prev = this;
              }
              unfinalized = this;
          }
      }
  
-     private void remove() {
-         synchronized (lock) {
-             if (unfinalized == this) {
-                 if (this.next != null) {
-                     unfinalized = this.next;
-                 } else {
-                     unfinalized = this.prev;
-                 }
-             }
-             if (this.next != null) {
-                 this.next.prev = this.prev;
-             }
-             if (this.prev != null) {
-                 this.prev.next = this.next;
-             }
-             this.next = this;   /* Indicates that this has been finalized */
-             this.prev = this;
-         }
-     }
- 
-     private Finalizer(Object finalizee) {
-         super(finalizee, queue);
-         add();
-     }
- 
      static ReferenceQueue<Object> getQueue() {
          return queue;
      }
  
      /* Invoked by VM */
      static void register(Object finalizee) {
          new Finalizer(finalizee);
      }
  
!     private void runFinalizer(JavaLangAccess jla) {
!         synchronized (this) {
!             if (hasBeenFinalized()) return;
!             remove();
          }
          try {
              Object finalizee = this.get();
              if (finalizee != null && !(finalizee instanceof java.lang.Enum)) {
                  jla.invokeFinalize(finalizee);
  
--- 34,91 ----
  final class Finalizer extends FinalReference<Object> { /* Package-private; must be in
                                                            same package as the Reference
                                                            class */
  
      private static ReferenceQueue<Object> queue = new ReferenceQueue<>();
+ 
+     /** Head of doubly linked list of Finalizers awaiting finalization. */
      private static Finalizer unfinalized = null;
+ 
+     /** Lock guarding access to unfinalized list. */
      private static final Object lock = new Object();
  
!     private Finalizer next, prev;
  
!     private Finalizer(Object finalizee) {
!         super(finalizee, queue);
!         // push onto unfinalized
          synchronized (lock) {
              if (unfinalized != null) {
                  this.next = unfinalized;
                  unfinalized.prev = this;
              }
              unfinalized = this;
          }
      }
  
      static ReferenceQueue<Object> getQueue() {
          return queue;
      }
  
      /* Invoked by VM */
      static void register(Object finalizee) {
          new Finalizer(finalizee);
      }
  
!     private void deregisterAndRunFinalizer(JavaLangAccess jla) {
!         synchronized (lock) {
!             if (this.next == this)      // already finalized
!                 return;
!             // unlink from unfinalized
!             if (unfinalized == this)
!                 unfinalized = this.next;
!             else
!                 this.prev.next = this.next;
!             if (this.next != null)
!                 this.next.prev = this.prev;
!             this.prev = null;
!             this.next = this;           // mark as finalized
          }
+         runFinalizer(jla);
+     }
+ 
+     private void runFinalizer(JavaLangAccess jla) {
          try {
              Object finalizee = this.get();
              if (finalizee != null && !(finalizee instanceof java.lang.Enum)) {
                  jla.invokeFinalize(finalizee);
  
*** 153,167 ****
                  // in case of recursive call to run()
                  if (running)
                      return;
                  final JavaLangAccess jla = SharedSecrets.getJavaLangAccess();
                  running = true;
!                 for (;;) {
!                     Finalizer f = (Finalizer)queue.poll();
!                     if (f == null) break;
!                     f.runFinalizer(jla);
!                 }
              }
          });
      }
  
      /* Invoked by java.lang.Shutdown */
--- 141,152 ----
                  // in case of recursive call to run()
                  if (running)
                      return;
                  final JavaLangAccess jla = SharedSecrets.getJavaLangAccess();
                  running = true;
!                 for (Finalizer f; (f = (Finalizer)queue.poll()) != null; )
!                     f.deregisterAndRunFinalizer(jla);
              }
          });
      }
  
      /* Invoked by java.lang.Shutdown */
*** 177,191 ****
--- 162,180 ----
                  if (running)
                      return;
                  final JavaLangAccess jla = SharedSecrets.getJavaLangAccess();
                  running = true;
                  for (;;) {
+                     // "pollFirst" from unfinalized
                      Finalizer f;
                      synchronized (lock) {
                          f = unfinalized;
                          if (f == null) break;
                          unfinalized = f.next;
+                         if (unfinalized != null)
+                             unfinalized.prev = null;
+                         f.next = f; // mark as finalized
                      }
                      f.runFinalizer(jla);
                  }}});
      }
  
*** 212,222 ****
              final JavaLangAccess jla = SharedSecrets.getJavaLangAccess();
              running = true;
              for (;;) {
                  try {
                      Finalizer f = (Finalizer)queue.remove();
!                     f.runFinalizer(jla);
                  } catch (InterruptedException x) {
                      // ignore and continue
                  }
              }
          }
--- 201,211 ----
              final JavaLangAccess jla = SharedSecrets.getJavaLangAccess();
              running = true;
              for (;;) {
                  try {
                      Finalizer f = (Finalizer)queue.remove();
!                     f.deregisterAndRunFinalizer(jla);
                  } catch (InterruptedException x) {
                      // ignore and continue
                  }
              }
          }