[PATCH] Fix multiple minor tzset glitches [BZ #24004]

[Paul Eggert]

On 2/18/19 1:37 AM, Florian Weimer wrote:
> I thought this polling (for reloading /etc/localtime if it has changed)
> was a feature.  I'm not sure if we can remove it.

No such polling is documented. On the contrary, the glibc manual says 
that an unset TZ is treated as if it were set to ':/etc/localtime'. 
There is no polling when you set TZ=':/etc/localtime' (or to 
TZ='/etc/localtime', or to any other value). So the code and the 
documentation disagree, and one or the other needs to be fixed.

Neither Solaris nor OpenBSD poll, so portable programs cannot assume 
that polling occurs. (These are the only two other systems I checked.)

Commentary like this:

https://blog.packagecloud.io/eng/2017/02/21/set-environment-variable-save-thousands-of-system-calls/

says that polling is a bad idea, and gives TZ=':/etc/localtime' as a 
workaround for glibc. I'm sympathetic, as the polling makes glibc look 
bad compared to the competition.