Re: Use of strbuf.buf when strbuf.len == 0

From: Pierre Habouzit <madcoder@debian.org>
Date: Sep 27, 2007, 10:13 UTC
Message-ID: <20070927101300.GD10289@artemis.corp>
In-Reply-To: <7vir5wy6fv.fsf@gitster.siamese.dyndns.org>

On Thu, Sep 27, 2007 at 06:21:24AM +0000, Junio C Hamano wrote:

Show 10 quoted lines

> It might be an easier and safer fix to define that strbuf_init()
> to always have allocation.  Use of a strbuf in the code _and_
> not adding any contents to the buffer should be an exception and
> avoiding malloc()/free() for that special case feels optimizing
> for the wrong case.
> 
> However, there are strbuf instances that are not initialized
> (i.e. in BSS or initialized by declaring with STRBUF_INIT), so
> we still need to handle (.len == 0 && .alloc == 0) case
> specially anyway.

  I can see a way, that would need special proof-reading of the strbuf
module, but should not harm its users, that would be to change
STRBUF_INIT to work this way:

  { .buf = "", .len = 0, .alloc = 0 }

  It needs to make strbuf_grow and strbuf_release check for ->alloc
before doing anything stupid.

  Though we may have some bits of code that rely on .buf being NULL if
nothing happened. I tried to track them down, but some may remain.

  If you agree with this change, that would solve most of the issues
with almost no cost, then I'll propose a new patch with this change.

-- 
·O·  Pierre Habouzit
··O                                                madcoder@debian.org
OOO                                                http://www.madism.org