[Pyobjc-dev] [ pyobjc-Bugs-735815 ] ivar leak & crash

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Bugs item #735815, was opened at 2003-05-10 22:34
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Just van Rossum (jvr)
Assigned to: Nobody/Anonymous (nobody)
Summary: ivar leak & crash

Initial Comment:
There is problem with assigning Python objects (that are not derived 
from NSObject) to ivars:

  >>> from objc import ivar
  >>> from Foundation import NSObject
  >>> class Foo(NSObject):
  ...   x = ivar("x")
  ... 
  >>> class Doo(object):
  ...   def __del__(self):
  ...     print "deleting Doo instance %x" % id(self)
  ... 
  >>> f = Foo.alloc().init()
  >>> f.y = Doo()  # assinging to non-ivar
  >>> f.y = 12
  deleting Doo instance 47bd10
  >>> f.x = Doo()  # assigning to ivar
  >>> f.x = 12  # look, no delete message
  >>> f.x = Doo()
  >>> del f.x
  Bus error

Two problems:
1) when *replacing* an ivar, the referenced object leaks
2) when *deleting* an ivar, there's a crash (btw. the bus error also
occurs if you try to delete an ivar that's not yet set (nil).

(Note that the leak does _not_ seem to occur when the referenced 
object's class is derived from NSObject, but the del crash occurs 
indepent of the type of the object.)

However, we have a bigger problem: ivars/outlets that are set by 
Cocoa during nib-awakening-time are weak references (not retained), 
so we can't simply release an ivar when we overwrite it with 
something else. Likewise during dealloc: currently ivars are _not_ 
released, which causes leaks for those ivars that are set from Python 
(x.y = z implies a retain for z).

Except perhaps for the Bus Error (which smells like a different 
problem altogether), these things are not easily fixed.

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