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Date: Wed, 04 Feb 2004 22:47:30 +0100
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Subject: Re: [PHP-DEV] New destructors implementation
From: cm@leetspeak.org (Michael Walter)

Hi Andi,

Andi Gutmans wrote:

 > [...]
 >
 > This has several implications:
 >
 > [...]

 >
 > 2.  A *VERY* important implication is that you cannot, and must not 
rely in any way on the order of destruction during shutdown.  It runs in 
no particular order.  That means that by the time the destructor for 
your object $foo is called,  a reference to some other object $bar may 
already be post-destruction.  Note that it will still be 'intact' and 
accessible in the sense that if you access it - there won't be crashes. 
  However, if this object does indeed have a destructor, it can be 
considered semantically wrong to touch this object at this point.

Doesn't that render more sophisticated cases of objects with 
constructors sort of unusable? I mean, any scheme like

class Wrapper:
   ctor: $this->m_resource=alloc_resource();
   dtor: $this->m_resource=free_resource();
   doWork(): do_this_and_that($this->m_resource);

class Client:
   ctor: $this->m_wrapper=new Wrapper();
   dtor: $this->m_wrapper->doWork();

is inherently unsafe, unless I totally got your message wrong (apologies 
  for potential confusion).

If you consider a common case such as the wrapper class wrapping a db 
connection or a file handle, and the client's destructor logging some 
"shutdown" message using that wrapper, I fail to realize how this would 
work with the given destructor scheme.

I'm not too familiar with the old destruction scheme, but wouldn't a 
destruction scheme in which not all object destructors are called still 
be superior to one which is completely non-deterministic in terms of 
shutdown order? Or probably better, how about at least trying to 
shutdown in reverse creation order (and for all cases for which that 
won't work, use the new non-deterministic scheme)?

 > [...]


Cheers,
Michael

PS: Apologies for obvious stupid remarks in this post, I'm sure I'm 
missing 1+ obvious issues