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  1. XMLBeans
  2. XMLBEANS-300

Threading issue leads to NPE in SchemaComponent$Ref.getComponent



    • Bug
    • Status: Resolved
    • Major
    • Resolution: Fixed
    • Version 2, Version 2.1, Version 2.2
    • Version 2.3
    • XmlObject
    • None


      We have seen this NPE during normal use of our application on a MP Solaris system using XmlBeans 2.0.0. I tested and confirmed it is still a problem in 2.2.0:

      at org.apache.xmlbeans.SchemaComponent$Ref.getComponent(SchemaComponent.java:104)
      at org.apache.xmlbeans.SchemaType$Ref.get(SchemaType.java:872)
      at org.apache.xmlbeans.impl.schema.SchemaPropertyImpl.getType(SchemaPropertyImpl.java:92)
      at org.apache.xmlbeans.impl.schema.SchemaTypeImpl.createElementType(SchemaTypeImpl.java:965)
      at org.apache.xmlbeans.impl.values.XmlObjectBase.create_element_user(XmlObjectBase.java:895)
      at org.apache.xmlbeans.impl.store.Xobj.getUser(Xobj.java:1592)
      at org.apache.xmlbeans.impl.store.Cur.getUser(Cur.java:2627)
      at org.apache.xmlbeans.impl.store.Cur.getObject(Cur.java:2620)
      at org.apache.xmlbeans.impl.store.Cursor._getObject(Cursor.java:983)
      at org.apache.xmlbeans.impl.store.Cursor.getObject(Cursor.java:2896)

      Here is how to reproduce with the debugger:

      • start two threads, each of which loads a different xml document with the same schema type
      • each thread will traverse its document, calling getObject at each element
      • break before traversal starts
      • insert breakpoint at SchemaComponent.java:104, and let both threads run to this point
      • resume one thread, and then the other
      • the second thread fails with the NPE

      Here is the code fragment from SchemaComponent $Ref:

      public final SchemaComponent getComponent()
      if (_schemaComponent == null && _handle != null)

      { _schemaComponent = _schemaTypeSystem.resolveHandle(_handle); // this is line 104 _schemaTypeSystem = null; }

      return _schemaComponent;

      Both threads use the same Ref object, and there is no protection between use of _schemaTypeSystem on line 104 and setting it null on the next line

      I do not know enough about how thread protection of schema types is designed to know if a localized fix to synchronize the lazy instantiation is appropriate, or if synchronization at a higher level is appropriate.


        1. XMLBEANS-300.patch.txt
          1 kB
          Ben La Monica



            Unassigned Unassigned
            geastman Gordon Eastman
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