time: New module

[Bruno Haible]

This set of patches introduces a new module 'time', that works around the
inconsistency of time(NULL) with gettimeofday().tv_sec and timespec_get().tv_sec
on glibc systems.

The replacement is a bit slower than the native glibc time(NULL) implementation
— 31 nanoseconds instead of 17 nanoseconds, according to Florian Weimer's
measurements
<https://sourceware.org/pipermail/libc-alpha/2023-March/146133.html>.

The new module is for those GNU programs that prefer to avoid trouble
due to clocks apparently going backwards.

As a bonus, it allows us to fix the test failures of the gettimeofday and
timespec_get tests that occurred with a probability between 0.1% and 0.3%
on glibc/Linux.


2023-03-08  Bruno Haible  <bruno@clisp.org>

        gettimeofday, timespec_get tests: Avoid test failure on glibc/Linux.
        * modules/gettimeofday-tests (Depends-on): Add 'time'.
        * modules/timespec_get-tests (Depends-on): Likewise.
        * tests/test-gettimeofday.c (test_consistency): Update comment.
        * tests/test-timespec_get.c (main): Likewise.

        time: Add tests.
        * tests/test-time.c: New file.
        * modules/time-tests: New file.

        time: New module.
        * lib/time.in.h (time): New declaration.
        * lib/time.c: New file.
        * m4/time_h.m4 (gl_TIME_H_REQUIRE_DEFAULTS): Initialize GNULIB_TIME.
        (gl_TIME_H_DEFAULTS): Initialize REPLACE_TIME.
        * m4/time.m4: New file.
        * modules/time-h (Makefile.am): Substitute GNULIB_TIME, REPLACE_TIME.
        * modules/time: New file.
        * tests/test-time-h-c++.cc: Check the signature of
        GNULIB_NAMESPACE::time.
        * doc/posix-functions/time.texi: Mention the glibc problem and the
        'time' module.

0001-time-New-module.patch
Description: Text Data

0002-time-Add-tests.patch
Description: Text Data

0003-gettimeofday-timespec_get-tests-Avoid-test-failure-o.patch
Description: Text Data