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

*** 23,32 ****
--- 23,34 ----
   * questions.
   */
  
  package java.lang.ref;
  
+ import java.util.function.Consumer;
+ 
  /**
   * Reference queues, to which registered reference objects are appended by the
   * garbage collector after the appropriate reachability changes are detected.
   *
   * @author   Mark Reinhold
*** 81,91 ****
          if (r != null) {
              head = (r.next == r) ?
                  null :
                  r.next; // Unchecked due to the next field having a raw type in Reference
              r.queue = NULL;
!             r.next = r;
              queueLength--;
              if (r instanceof FinalReference) {
                  sun.misc.VM.addFinalRefCount(-1);
              }
              return r;
--- 83,93 ----
          if (r != null) {
              head = (r.next == r) ?
                  null :
                  r.next; // Unchecked due to the next field having a raw type in Reference
              r.queue = NULL;
!             r.next = Reference.DEQUEUED;
              queueLength--;
              if (r instanceof FinalReference) {
                  sun.misc.VM.addFinalRefCount(-1);
              }
              return r;
*** 162,167 ****
--- 164,188 ----
       */
      public Reference<? extends T> remove() throws InterruptedException {
          return remove(0);
      }
  
+     /**
+      * Iterate queue and invoke given action with each Reference.
+      * Suitable for diagnostic purposes.
+      */
+     void forEach(Consumer<? super Reference<? extends T>> action) {
+         for (Reference<? extends T> r = head; r != null;) {
+             action.accept(r);
+             Reference rn = r.next;
+             if (rn == r) {
+                 // end of chain
+                 r = null;
+             } else if (rn == Reference.DEQUEUED) {
+                 // restart from head if overtaken by queue poller(s)
+                 r = head;
+             } else {
+                 r = rn;
+             }
+         }
+     }
  }