Catch possible NPE in Memory#close if Cleaner runs first

Author: dbwiddis

CHANGES.md

@@ -10,7 +10,7 @@ Features
 
 Bug Fixes
 ---------
-
+* [#1447](https://github.com/java-native-access/jna/issues/1447): Catch possible NPE in `c.s.j.Memory#close` if Cleaner runs first - [@dbwiddis](https://github.com/dbwiddis).
 
 Release 5.12.0
 ==============

src/com/sun/jna/Memory.java

@@ -22,7 +22,6 @@
  */
 package com.sun.jna;
 
-import com.sun.jna.internal.Cleaner;
 import java.io.Closeable;
 import java.lang.ref.Reference;
 import java.lang.ref.WeakReference;
@@ -32,6 +31,8 @@
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 
+import com.sun.jna.internal.Cleaner;
+
 /**
  * A <code>Pointer</code> to memory obtained from the native heap via a
  * call to <code>malloc</code>.
@@ -180,9 +181,14 @@ public Memory align(int byteBoundary) {
     }
 
     /** Free the native memory and set peer to zero */
+    @Override
     public void close() {
         peer = 0;
-        cleanable.clean();
+        try {
+            cleanable.clean();
+        } catch (NullPointerException npe) {
+            // If Cleaner has removed the reference it is null, ignore
+        }
     }
 
     @Deprecated
@@ -783,6 +789,7 @@ public MemoryDisposer(long peer) {
             this.peer = peer;
         }
 
+        @Override
         public synchronized void run() {
             try {
                 free(peer);