How is time zone change signalled?

[Greg Larkin]

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Peter Steele wrote:
>> Did you try unsetting TZ and then calling tzset()?  The man page
> implies that doing so will force a reread of /etc/localtime
>> (http://www.freebsd.org/cgi/man.cgi?query=tzset&sourceid=opensearch):
>>
>> "The tzset() function initializes time conversion information used by
> the library routine localtime(3).  The environment variable TZ specifies
> how this is done.
>> If TZ does not appear in the environment, the best available
> approximation to local wall clock time, as specified by the
> tzfile(5)-format file /etc/localtime is used."
>> I haven't tested it, though, and I'm no timezone expert, so I may be
> completely off-base!
> 
> Yes, I've tried the tzset function. I'm basically doing the equivalent
> of these steps after the Java app changes time zone and updates
> /etc/localtime:
> 
> 	time_t date = time(NULL);
> 	unsetenv("TZ");
> 	tzset();
> 	printf("time zone is %s/%s", tzname[0], tzname[1]);
> 	struct tm* locTime = localtime(&date);
> 	printf("%02d:%02d:%02d", locTime->tm_hour, locTime->tm_min,
> locTime->tm_sec);
> 
> The time printed is still based on the old time zone though. The tzname
> variable that is set by tzset() still shows for example EDT even if I
> have just changed the time zone to PDT. If I stop and restart the C app,
> the time is correct, and tzname is then PDT instead of EDT.
> 
> I'm very puzzled on what I'm supposed to do to kick start the C time
> zone. We do not want to have to restart our C apps for something as
> trivial as this.
> 

Hi Peter,

Ok, just wanted to make sure you tried unsetting TZ before calling
tzset().  I couldn't tell from your original message.  In any case, the
man page makes it sound like it should work.

I'm really rusty on C programming, but I had a look in
/usr/src/lib/libc/stdtime/localtime.c, and it appears that
/etc/localtime should be reloaded, although this comment at the
beginning of tzload() gives me pause:

/* XXX The following is from OpenBSD, and I'm not sure it is correct */

I wonder if you'd get more insight by asking the question in -hackers.
Perhaps there are some libc experts listening there.

Cheers,
Greg
- --
Greg Larkin

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http://www.sourcehosting.net/ - Ready. Set. Code.
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