[Xotcl] Garbage Collector in Xotcl

Artur Trzewik mail at xdobry.de
Sun May 20 12:39:21 CEST 2001


The really problem of Xotcl is, it has no garbage collector.
It means you must destroy your object yourself per destroy method.

The garbage collector of such languages as Java, smalltalk, ruby work by
tracking references to one object. if no reference point to object, this 
object is destroyed.

This would not work by xotcl. Xotcl object are localized per name (string)
and no reference. (And it is very flexible in most cases)
It can by hardly changed.
It is pity, if one consider that tcl has internal full garbage collector 
based on Tcl_Obj (structure) with references counter.

This problem is no so dramatic if one use object aggregation.
So the aggregated object is deleted automatically if parent object
is to be destroyed.
But is can be rather hard by using "short-live" object (for example by
implementing special data structures in Xotcl).

The solution of this problem can be to add new create method in Xotcl.
To create object to use only as reference.
It means object lives only so long if the reference exist.
It will use internal standard tcl structures (as Tcl Stings, Integer, Arrays)

example usage

proc exampleScope {} {
     # create short-live Object for reference
    set ref [Object newReference]
    # using object
    $ref set var 11
    # be exit the object referenced by variable ref 
    # will be deleted automatically

The best think is one can choose to use garbage collector
or not.
>Object newReference
will for example create one object and destroy it immediately.
So in such case the old method
>Object new
should be used.

Internal implementation.

The main thing is to tread Xotcl objects in the same way
as other tcl objects (Stings, Interger, Array) and use tcl garbage collector
I thing there should be a wrapper Tcl_Obj (new Type)

Here only the main idea
static Tcl_ObjType XOTclReferenceObjectType = {
  (Tcl_FreeInternalRepProc *) ourNewDestroyMethod,
  (Tcl_DupInternalRepProc *) NULL,

The newReference method must create such reference Tcl_Obj
and return it as result. Of course newReference must be implemented
in C in libxotcl.so.

What do you think about it?
I mean I can implement it but I am not sure how it would suite to another 
concepts or future plans.
For example for xotcl objects created per newReference the destroy method make
no sense.
It can make also another problems that should be discused.


 Artur Trzewik 


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