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by hodgesrm 3401 days ago
Interesting article but I can't reproduce the behavior on Ubuntu 16.01 LTS. I don't have TZ set (or anything locale-related for that matter). Here are the library dependencies:

  $ ldd test
  linux-vdso.so.1 =>  (0x00007ffd80baf000)
  libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f8844bf7000)
  /lib64/ld-linux-x86-64.so.2 (0x00007f8844fbc000)
Any thoughts why the behavior would be different?
1 comments
cnvogel 3401 days ago
There's also a surprising difference in behavior between tm = localtime() and localtime_r(..., &tm).

The former is the "traditional" function which returns a pointer to a statically allocated, global "struct_tm". The latter is the thread-safe version receiving a pointer to a use-supplied "struct tm" as it's second argument.

    :   do {
    :           t = time(NULL);
    :           localtime_r(&t, &tm);
    :           printf("The time is now %02d:%02d:%02d.\n",
    :                  tm.tm_hour, tm.tm_min, tm.tm_sec);
    :           sleep(1);
    :   } while(--N);
with TZ set to Europe/Berlin, set to :/etc/localtime, or unset I never get a stat on anything.

    write(1, "The time is now 07:23:33.\n", 26The time is now 07:23:33. ) = 26
    nanosleep({tv_sec=1, tv_nsec=0}, 0x7ffd9e798470) = 0
    write(1, "The time is now 07:23:34.\n", 26The time is now 07:23:34. ) = 26
    nanosleep({tv_sec=1, tv_nsec=0}, 0x7ffd9e798470) = 0
    write(1, "The time is now 07:23:35.\n", 26The time is now 07:23:35. ) = 26
    nanosleep({tv_sec=1, tv_nsec=0}, 0x7ffd9e798470) = 0
If I change it to tm = localtime()...

    stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2335, ...}) = 0
    write(1, "The time is now 07:30:56.\n", 26The time is now 07:30:56.) = 26
    nanosleep({tv_sec=1, tv_nsec=0}, 0x7ffc868c3010) = 0
One more reason to switch to the reentrant/thread-safe versions of those ugly library functions :-).

Note, this is using glibc 2.24 under Arch.

    $ /lib/libc.so.6
    GNU C Library (GNU libc) stable release version 2.24, by Roland McGrath et al.
    (...)
    Compiled by GNU CC version 6.1.1 20160802.
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