[bug #6743] Distinct NSNumbers with the same value dealloc each other

[nobody]

=================== BUG #6743: LATEST MODIFICATIONS ==================
http://savannah.gnu.org/bugs/?func=detailbug&bug_id=6743&group_id=99

Changes by: David Ayers <d.ayers@inode.at>
Date: Tue 11/25/2003 at 12:09 (Europe/Vienna)

------------------ Additional Follow-up Comments ----------------------------
Yes, that would be very good.



=================== BUG #6743: FULL BUG SNAPSHOT ===================


Submitted by: moseshall               Project: GNUstep                      
Submitted on: Tue 11/25/2003 at 04:06
Category:  Base/Foundation            Severity:  5 - Major                  
Bug Group:  Bug                       Resolution:  None                     
Assigned to:  None                    Status:  Open                         

Summary:  Distinct NSNumbers with the same value dealloc each other

Original Submission:  Distinct NSNumbers with the *same value* can dealloc each 
other. The following code snippet crashes gnustep-base 1.7.3 possibly because 
of NSNumber caching. If I don't call [n1 release] there is no crash. If this is 
due to caching strategy, then it can make NSNumber very fragile when numbers 
are expected to persist as long as retained.



#include <Foundation/Foundation.h>



int main (int argc, const char *argv[], const char *env[]) 

{

  NSNumber* n1 = [NSNumber numberWithLong:1];

  NSNumber* n2 = [NSNumber numberWithLong:1];

  NSLog(@"%@(%d)n", n1, [n1 retainCount]);

  NSLog(@"%@(%d)n", n2, [n2 retainCount]);

  [n1 release]; //<--problem here

  // The next line crashes. n2 has gone away!

  NSLog(@"%@(%d)n", n2, [n2 retainCount]);

  return 0;

}



Thanks for your attention.

Brian 'Moses' Hall

moses@blugs.com

Follow-up Comments
*******************

-------------------------------------------------------
Date: Tue 11/25/2003 at 12:09       By: ayers
Yes, that would be very good.

-------------------------------------------------------
Date: Tue 11/25/2003 at 11:40       By: CaS
What I was thinking of was making the cached numbers members of some new 
subclass where -dealloc had been overridden to raise an exception.  So there 
would be no runtime overhead on dealloc of a non-cached number.

-------------------------------------------------------
Date: Tue 11/25/2003 at 11:17       By: ayers
In principal I agree, but it depends on the cost.  I'm not sure how much the 
hit would be, but expect numbers to be created and destroyed often in GDL2 
based applications.  So if each dealloc resulted in a hash look up... well, 
depending on the implementation, I guess we may need to test it.

-------------------------------------------------------
Date: Tue 11/25/2003 at 09:00       By: CaS
I think raising an exception upon an attempt to deallocate a cached NSNumber 
would be a nice feature.

-------------------------------------------------------
Date: Tue 11/25/2003 at 07:24       By: CaS
There is a bug in the test program ... it releases an object it does not own, 
so a crash does not seem unreasonable (in the general case releasing objects 
you don't own is bound to cause crashes).



Is the report a suggestion that the library should be changed to crash 
elsewhere, or to have code added to watch for this case and raise an exception 
or something similar, or perhaps to simply ignore the extra release and keep on 
going?




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