Here is a patch for using gmtime_r() and localtime_r() instead of gmtime() and localtime(), for thread-safety.
There are a few affected calls in libpq and ecpg's libpgtypes, which are probably effectively bugs, because those libraries already claim to be thread-safe.
There is one affected call in the backend. Most of the backend otherwise uses the custom functions pg_gmtime() and pg_localtime(), which are implemented differently.
Some portability fun: gmtime_r() and localtime_r() are in POSIX but are not available on Windows. Windows has functions gmtime_s() and localtime_s() that can fulfill the same purpose, so we can add some small wrappers around them. (Note that these *_s() functions are also different from the *_s() functions in the bounds-checking extension of C11. We are not using those here.)
MinGW exposes neither *_r() nor *_s() by default. You can get at the POSIX-style *_r() functions by defining _POSIX_C_SOURCE appropriately before including <time.h>. (There is apparently probably also a way to get at the Windows-style *_s() functions by supplying some additional options or defines. But we might as well just use the POSIX ones.)
Hi! Looks good to me.
But why you don`t change localtime function at all places?
