Re: How to signal a time zone change?
On Fri, 7 Aug 2009 15:08:16 -0700 Peter Steele
pste...@webmail.maxiscale.com wrote:
What's the value of the TZ environment variable for the C apps? You may
need to have them read the new value from somewhere, and then rerun
tzset().
The default value of the TZ environment variable is null. I just tried
passing the explicitly time zone value to the C app and setting TZ to
that value and that seemed to work. I would think that that I should be
able to retrieve that value from /etc/localtime as the docs imply. Guess
not. If I have to pass the time zone to the C app, then I guess that's
what I'll do...
This doesn't work because of two bugs in localtime.c. The first is what
you're hitting where tzset() calls tzset_basic() which calls tzsetwall_basic()
which says:
if (lcl_is_set 0) {
if (!rdlocked)
_RWLOCK_UNLOCK(lcl_rwlock);
return;
}
If you were to have your own TZ setting and wanted to modify the
file referred to by that, you'd bump into this bug in tzset_basic():
if (lcl_is_set 0 strcmp(lcl_TZname, name) == 0) {
if (!rdlocked)
_RWLOCK_UNLOCK(lcl_rwlock);
return;
}
Roughly translated, localtime.c goes out of its way to never re-read the
same zone file twice in a row. This is just a mistake.
As you discovered, altering TZ before calling tzset() is the best way to
make it work right now. If you really want to ensure that you're reading
/etc/localtime, this bit of hackery works too:
putenv(TZ=/dev/null);
tzset();
unsetenv(TZ);
tzset();
If you raise a PR and let me know the number, I'd be happy to fix this.
--
Brian Somers br...@awfulhak.org
Don't _EVER_ lose your sense of humour ! br...@freebsd.org
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How to signal a time zone change?
We have a suite of applications with a Java GUI controlling everything. One of the actions the user can perform is to set the time zone. We do this through our Java application and update the /etc/localtime as required. We also make an API call to tell the JVM that the time zone as changed, and from the perspective of the Java app, the time zone is changed correctly (the timestamps for example in our log files reflect the change). Likewise, after the user performs this action, running date on one of our systems shows that the time zone has been changed as requested. The problem is with our C applications. They continue to operate with the old time zone, so things like timestamps in log files are not in sync with the timestamps in the Java app log files. If we stop and restart the C apps they pick up the time zone change. However, we don't want to take this extreme approach. We want the Java app to signal to the C applications that the time zone has changed. However, I've experimented with the various time zone related calls and I cannot figure out what call is needed to make the C applications pick up the time zone change. I've tried setting the environment variable TZ to the new time zone and this doesn't seem to work, and I've tried calling tzset() and tzsetwall(). In each case after I make these calls the function localtime() does not return the same time base as the Java application. Based on what I've read, I would think that the following steps would do the trick on the C side 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 in this example however is still based on the old time zone. 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 time zone change in C. We do not want to have to restart our C apps for something as trivial as this. I posted this originally to the questions list but didn't get much traction. I'm hoping someone on this list can point me in the right direction. ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to freebsd-hackers-unsubscr...@freebsd.org
Re: How to signal a time zone change?
Peter Steele wrote: We have a suite of applications with a Java GUI controlling everything. One of the actions the user can perform is to set the time zone. We do this through our Java application and update the /etc/localtime as required. We also make an API call to tell the JVM that the time zone as changed, and from the perspective of the Java app, the time zone is changed correctly (the timestamps for example in our log files reflect the change). Likewise, after the user performs this action, running date on one of our systems shows that the time zone has been changed as requested. The problem is with our C applications. They continue to operate with the old time zone, so things like timestamps in log files are not in sync with the timestamps in the Java app log files. If we stop and restart the C apps they pick up the time zone change. However, we don't want to take this extreme approach. We want the Java app to signal to the C applications that the time zone has changed. However, I've experimented with the various time zone related calls and I cannot figure out what call is needed to make the C applications pick up the time zone change. I've tried setting the environment variable TZ to the new time zone and this doesn't seem to work, and I've tried calling You need to signal your app in some way.. Assuming you have source for the app then you can monitor /etc/localtime (or /etc) for change with kevent. ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to freebsd-hackers-unsubscr...@freebsd.org ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to freebsd-hackers-unsubscr...@freebsd.org
RE: How to signal a time zone change?
You need to signal your app in some way.. Assuming you have source for the app then you can monitor /etc/localtime (or /etc) for change with kevent. Signaling our C apps aren't the problem. We have an IPC framework in place and we can easily tell the C apps when the user has changed the time zone via the GUI. The problem is I can't figure out what C calls are needed to instantiate the time zone change. Based on the documentation, I would think that tzset() would do the trick once /etc/localtime has been updated by the Java app, but this does not work. The only way I've discovered that works is to restart our C apps and we want to avoid that. ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to freebsd-hackers-unsubscr...@freebsd.org
RE: How to signal a time zone change?
What's the value of the TZ environment variable for the C apps? You may need to have them read the new value from somewhere, and then rerun tzset(). The default value of the TZ environment variable is null. I just tried passing the explicitly time zone value to the C app and setting TZ to that value and that seemed to work. I would think that that I should be able to retrieve that value from /etc/localtime as the docs imply. Guess not. If I have to pass the time zone to the C app, then I guess that's what I'll do... ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to freebsd-hackers-unsubscr...@freebsd.org
