heap_gc behaviour

[rother(at)gfz-potsdam.de]

   hi!

   just bothered by the spawn bug in IDL 5.3 (formatted I/O in bidirectional
   pipes crashes IDL...)
   I detected now a 'heap_gc' behaviour, which I don't *understand*,
   but I'm *not sure* if this is a bug, an annoying feature or ...

   A call of 'heap_gc' inside a routine destroys a
   a heap-variable given as parameter.... ?

   Yes, I have read the reference manual... but as long I understand
   a call of 'heap_gc' inside a function is not forbidden.

   I add here a small demonstration: a 'batch', a tiny function which is 
   called and the IDL messages.

   any hints?
   thanks in advance,
   martin rother.

**** this3.pro

PRO this3, foo
;+=============================================================================
;
;    * SCRATCH: TEST HEAP_GC ONLY *
;    Sparc, Solaris, IDL 5.3
;
;    input:
;
;       foo       pointer?   to heap
;       count     integer    counter, modify foo if zero and
;                            call heap_gc
;
;    00-Apr-04 Martin Rother (rother@gfz-potsdam.de).
;-=============================================================================

   ON_ERROR, 2

   print, 'have: '                    & help, *foo
   print, 'call garbage collection: ' & heap_gc 
   print, 'have: '                    & help, *foo
   return 

END
;==============================================================================

*** test3

;==============================================================================
;
;    TEST3
;
;    00-Apr-04 
;==============================================================================

   .r this3.pro

   ;---------------------------------------------------------------------------
   ; simple heap var
   ;---------------------------------------------------------------------------

   foo = ptr_new(dist(12))   

   ;---------------------------------------------------------------------------
   ; CALL
   ;---------------------------------------------------------------------------

   print, 'top level:' & help, *foo

   this3, foo

   print, 'top level:' & help, *foo

;==============================================================================

**** IDL output:

(X). @test3
top level:
<PtrHeapVar4>   FLOAT     = Array[12, 12]
have: 
<PtrHeapVar4>   FLOAT     = Array[12, 12]
call garbage collection: 
have: 
% Invalid pointer: FOO.
% Error occurred at:  THIS3              19
  /home/mt/rother/idl/Test/heap_test/this3.pro
%                     $MAIN$                 
% Execution halted at:  $MAIN$                 
top level:
% Invalid pointer: FOO.
% Execution halted at:  $MAIN$                 
(X). 

-- 
Martin Rother (rother@gfz-potsdam.de)   0331/ 288-1272           Division 2.3
                                        GeoForschungsZentrum Potsdam, Germany