Re: [PATCH] Add and use _REENT_GLOBAL_ATEXIT

[Sebastian Huber <sebastian dot huber at embedded-brains dot de>]

On 05/02/2013 09:36 PM, Jeff Johnston wrote:
> I would like to change this.
>
> I don't like having a macro that takes a ptr argument and ignores it.  I also
> would prefer consistency with the impure ptr struct declarations. The atexit0
> storage is supposed to be statically guaranteed which is currently accomplished
> by being part of the static global reent struct.

The problem is that with the current struct _reent you have per-reent atexit 
support.  I don't know if this is used in code outside of Newlib by some 
system.  You can for example add your own my_thread_atexit() which registers 
atexit() handlers in the thread-local reent which are called during thread 
delete via my_thread_delete_call_atexit().  The patch will be simpler if we 
accept to break such systems.

> My preference is that you declare a static atexit0_data struct inside impure.c
> along-side the impure_data declaration (being controlled by your new
> _REENT_GLOBAL_ATEXIT macro).

If we place it in impure.c, then we need this space even if nobody calls atexit().

> Then, you have two macros:
>
> _GLOBAL_ATEXIT  (which is either _GLOBAL_REENT->_atexit or _impure_atexit
> (whatever you call it), which is also declared in impure.c based on the
> _REENT_GLOBAL_ATEXIT macro.
>
> and
>
> _GLOBAL_ATEXIT0 (which is either &(_GLOBAL_REENT->_atexit0) or the address of
> _impure_atexit0_data or whatever you put in impure.c for atexit0).
>
> It becomes relatively straightforward after that to change the existing code.

In _reclaim_reent() we have "&ptr->_atexit0".  Changing this to 
"&(_GLOBAL_REENT->_atexit0" alters the behaviour.

> I probably would not have bothered moving the _atexit pointer out of the struct
> myself since it is such a minor gain compared to the atexit0 savings but whatever.

Yes, it saves only some bytes, but this enforces that the atexit() support is 
no longer potentially thread-local.

--
Sebastian Huber, embedded brains GmbH

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