localtime() vs localtime_r()

[Peter Jeremy]

On Mon, Mar 31, 2008 at 11:36:36AM +0800, David Xu wrote:
>According POSIX specification, it seems localtime_r() is not only
>a reentrant version of localtime(), but also a performance-wise version.

IMO, localtime_r() is _not_ reentrant because it implicitly uses TZ
from the environment, rather than having TZ (ither as TZ or struct
state) passed as an argument.  I have an application that does
conversions between timezones and this lack is a PITA.

>Our implementation does set tzname, tomezone and daylight, it is a bit
>slower than glibc because ours has to call getenv() everytime.

Given that POSIX stuffed the definition of localtime_r(), it's not
clear how to avoid this.  I guess you could change the tzset_basic()
call in localtime_r() to something like:
	static initialised = 0;
	if (!initialised) {
		tzset_basic();
		initialised = 1;
	}
which means it won't see changes to TZ.

-- 
Peter Jeremy
Please excuse any delays as the result of my ISP's inability to implement
an MTA that is either RFC2821-compliant or matches their claimed behaviour.
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