How is time zone change signalled?

[Peter Steele]

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.

 

I'm obviously missing something the key here. What function call do I
need to make to get the C apps to pick up the time zone change?