src/share/classes/sun/nio/cs/AbstractCharsetProvider.java

@@ -177,12 +177,14 @@
                     return i.hasNext();
                 }
 
                 public Charset next() {
                     String csn = i.next();
+                    synchronized (AbstractCharsetProvider.this) {
                     return lookup(csn);
                 }
+                }
 
                 public void remove() {
                     throw new UnsupportedOperationException();
                 }
             };