On Mon, Apr 22, 2013 at 01:45:52AM +0000, YAMAMOTO Takashi wrote: > > On Thu, Apr 18, 2013 at 06:58:42AM +0000, YAMAMOTO Takashi wrote: > >> > On Tue, Apr 16, 2013 at 11:34:52PM +0000, YAMAMOTO Takashi wrote: > >> >> > On Tue, Apr 16, 2013 at 11:39:50PM +0900, Takehiko NOZAKI wrote: > >> >> >> so that the struct _locale __C_locale in libc is much more wasteful. > >> >> > > >> >> > I should add that it is an internal detail and the way the composed C > >> >> > locale is stored can and likely will change later. So the way it is > >> >> > essentially a copy of (old) global locale is just a way to be > >> >> > minimally > >> >> > intrusive. > >> >> > > >> >> > Joerg > >> >> > >> >> i care the API. > >> >> > >> >> if you really want it be in libc, how about having libc provide a > >> >> "locale_t get_static_c_locale();" style API rather than using NULL? > >> >> it's better because 1) less code in *_l, 2) autoconf-like can detect > >> >> the extension easily, and 3) a portable application can trivially > >> >> have a fallback implementation using newlocale+pthread_once. > >> > > >> > It adds more cost on the caller side. So far, there are three mechanisms > >> > available (especially for libraries): > >> > > >> > (1) Adhoc access to internal locale state. This is used with glibc. > >> > (2) Explicit newlocale(). > >> > (3) Implicit access via 0 argument to *_l. > >> > > >> > The first one is clearly a hack and not acceptable. Portable code can > >> > always conditionally use (2), but it requires additional setup and > >> > storage cost. (3) is used by Apple (which is where a large part of the > >> > *_l interface originates from) and FreeBSD. It is orthogonal to (2) and > >> > certainly easier to use. Exposing it via a special library call is also > >> > possible and effectively a way to implement (2) by a static wrapper. > >> > It still adds more cost to every caller and this is a classic case where > >> > there are typically much more callers. > >> > > >> > Joerg > >> > >> (3) adds small costs to every calls of *_l, even when the extension > >> is not used. i sounds worse than a one-time cost of (2) to me. > > > > (2) still needs to load the address (instead of a constant), so it isn't > > free either. Given that this is very popular as functionality and at > > least on modern CPUs often implementable as conditional-move, it sounds > > like a much better trade off. > > very popular? i'm not aware of a single software which uses this extension. > can you provide examples?
The "very popular" specifically applies to the need for accessing the C locale. Most bigger libraries need it one way or another. I am currently talking with Apple about providing a visible macro (LC_C_LOCALE) to address the testability issue. Joerg
