Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!crdgw1!uunet!mcsun!ukc!tcdcs!bofin!mmartin
From: mmartin@cs.tcd.ie (Maurice Martin)
Newsgroups: comp.lang.eiffel
Subject: Eiffel Runtime - Object Header Question
Summary: A question on how the `nobj' field of OBJECT, is used
Keywords: Internal, Runtime, Memory Management
Message-ID: <1991Apr15.170027.8088@cs.tcd.ie>
Date: 15 Apr 91 17:00:27 GMT
Organization: DSG, Dept. of Comp. Sci., Trinity College, Dublin.
Lines: 33


Background: Using the normal memory management routines on the DEC5810
            MIPS implementation of Eiffel (i.e. 32 bit word size), each 
            object has a 64 bit object header, defined by the following 
            struct:


            OBJECT = struct {
                               INFO info ; -- INFO == int32
                               struct OBJECT* nobj;
                            }

Question: Apart from garbage collection, what is the pointer ``nobj''
          used for ?

Partial Answer: It appears as if all objects in an eiffel system are
	            chained together via the nobj field. This is used during
	            garbage collection. Also the environment and storable
	            classes seem to reference the field.  It also appears to be
	            used in connection with EXPANDED classes.  I do not
                follow exactly how nobj and expanded classes inter-relate.


-- If I have got `nobj's uses wrong, or missed some, please correct me!

Thanks in Advance,

=======================================================================
 Maurice Martin                  email:  mmartin@cs.tcd.ie
 Distributed Systems Group       fax  :  + 353-1-772204
 O'Reilly Institute, T.C.D.      phone:  + 353-1-772941 x1524  (day)
 Dublin 2, IRELAND.                      + 353-1-462681        (evening)
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