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authorHiltjo Posthuma <hiltjo@codemadness.org>2021-01-10 16:57:53 +0100
committerHiltjo Posthuma <hiltjo@codemadness.org>2021-01-10 18:49:21 +0100
commitf18f4818ed2c992aa9b7b91c74bb9ce7cc1bc745 (patch)
treeda9d7e335d7f6daeca3360820ea2013663f8a769 /doc/html
parentc1b44cf790f8090ff25a2ff268c3f7a8d53e1bcf (diff)
optimize converting UNIX timestamp to localtime
Make a huge difference (cuts the time in half to process the same amount of lines) on atleast glibc 2.30 on Void Linux. Seems to make no difference on OpenBSD. - This removes atleast one heap allocation per line (checked with valgrind). This is because glibc will strdup() the environment variable $TZ and free it each time, which is pointless here and wasteful. - localtime_r does not require to set the variables like tzname. In glibc-2.30/time/tzset.c in __tz_convert is the following code and comment: /* Update internal database according to current TZ setting. POSIX.1 8.3.7.2 says that localtime_r is not required to set tzname. This is a good idea since this allows at least a bit more parallelism. */ tzset_internal (tp == &_tmbuf && use_localtime); This makes it always tzset() and inspect the environment $TZ etc. While with localtime_r it will only initialize it once: static void tzset_internal (int always) { [...] if (is_initialized && !always) return;
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