Re: RFC: glocal - automatically freeing memory when it goes out of scope

On 05/29/2012 10:21 PM, Ben Pfaff wrote:
Mikkel Kamstrup Erlandsen<mikkel kamstrup canonical com>  writes:

On 05/29/2012 07:23 PM, Ben Pfaff wrote:
Mikkel Kamstrup Erlandsen<mikkel kamstrup canonical com>   writes:

I have been looking at gcc's "cleanup" attribute[1] that allows one to
specify a callback that will be invoked when a variable goes out of
scope. This allows one to play with automatically freeing resources.

Is it possible to combine use of this GCC-specific attribute with
the concept in Doug Gwyn's "mostly-portable" alloca
implementation, so that you would end up with something that
works pretty much everywhere (but is more efficient with GCC)?

Here's one copy of the Doug Gwyn alloca that just happened to be
on the top of the results of my web search:

There is already g_alloca() and g_newa() for allocating on the stack.

I'm not suggesting an implementation of an alloca-like function
based on these ideas; as you say, glib already has alloca-like

I'm suggesting that one could use the idea behind the Doug Gwyn
portable alloca to implement something like, or at least related
to, the GCC "cleanup" attribute even when GCC is not the compiler
in use.  (However, the attribute syntax wouldn't work, and the
interface would otherwise need to be different.)

Sorry, I misunderstood you then :-) I am afraid the answer is no.

alloca() does not provide a callback when cleaning up, and we need that for anything that needs a teradown function - which is basically everything that is not a string...

Also this portable alloca() mentions in the docs that memory is not guaranteed to be freed when you leave the scope, but mayb happen higher up in the stack - and there even should be a mainloop driving "garbage collection" with alloca(0) as well. This means that the automagic lock management I added wouldn't work fx.


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