From Newsgroup: comp.lang.tcl

I have some unexèpected result with this (over-simplified) C code (using
the Tcl-C API), and I don't understandard what's wrong.

Please could you tell me what's wrong with this Tcl-C code ?

--
This is (in plain Tcl) what I'm trying to achive.
This may seem silly, but it's just an oversimplified case.

----
proc fun {} {
# build a list of values
set A [list]
foreach element {100.0 200.0 300.0} { lappend A $element }

# -- now extract and return the 1st element
set v [lindex $A 0]
return $v
}
----
And here's its adaption in C (using the Tcl-C API)

---
int CMD_fun { ClientData clientData, Tcl_Interp *interp, int argc, const
char *argv[]) {
Tcl_Obj* aList = Tcl_NewListObj(0,NULL);
for (int i=1 ; i <= 3; ++i) {
Tcl_ListObjAppendElement(interp, aList , Tcl_NewDoubleObj(i*100.0));
}

//extract the 1st element (-> 100.0) and incr its RefCount
Tcl_Obj* resultObj;

Tcl_ListObjIndex(interp,aList,0,&resultObj);
Tcl_IncrRefCount(resultObj);

// free aList
Tcl_DecrRefCount(aList); // the listObj, and all its elements are released, but the first

Tcl_SetObjResult( interp, resultObj );
return TCL_OK;
}
..
Tcl_CreateObjCommand( interp, "cfun" , CMD_fun, (ClientData)NULL, (Tcl_CmdDeleteProc *)NULL) ;
..
---
This works as expected (return 100.0), but if called 100.000 times,
I see an abnormal growth in memory (Megabytes).

What's wrong ?
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From Newsgroup: comp.lang.tcl

On 05/03/2025 21:41, abu wrote:

This works as expected  (return 100.0), but if called 100.000 times,
I see an abnormal growth in memory (Megabytes).

What's wrong ?

For one thing, your reference count on resultObj is too high. You did an explicit Tcl_IncrRefCount() and Tcl_SetObjResult() increments it again.
It now has a count of 2. When the code that invoked the cfun command is
done with the result, it lowers the reference count by one. But that
does not free the Tcl_Obj, because it still has a reference count of 1.
As a Tcl_Obj takes 24 bytes on a 32-bit system (and more on a 64-bit
system), this would add up to a few megabytes when called 100.000 times.

Either skip the Tcl_IncrRefCount() and run Tcl_SetObjResult() before the Tcl_DecrRefCount() on aList, or do a Tcl_DecrRefCount() on resultObj
after the Tcl_SetObjResult() call.


Schelte.

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From Newsgroup: comp.lang.tcl

Thank you. It was so simple !
Now it works !
Thank you again.

Aldo
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