commit | 370ddcbc89646c7f53728ec7d1fb87597b52de67 | [log] [tgz] |
---|---|---|
author | Paul Eggert <eggert@cs.ucla.edu> | Mon Mar 20 16:05:07 2023 -0700 |
committer | Junio C Hamano <gitster@pobox.com> | Tue Mar 21 13:11:42 2023 -0700 |
tree | b4a3e43ee9622f7e43dc62e1326077c72c3acf73 | |
parent | 73876f4861cd3d187a4682290ab75c9dccadbc56 [diff] |
git-compat-util: use gettimeofday(2) for time(2) Use gettimeofday instead of time(NULL) to get current time. This avoids clock skew on glibc 2.31+ on Linux, where in the first 1 to 2.5 ms of every second, time(NULL) returns a value that is one less than the tv_sec part of higher-resolution timestamps such as those returned by gettimeofday or timespec_get, or those in the file system. There are similar clock skew problems on AIX and MS-Windows, which have problems in the first 5 ms of every second. Without this patch, users can observe Git issuing a timestamp T+1 before it issues timestamp T, because Git sometimes uses time(NULL) or time(&t) and sometimes uses higher-res methods like gettimeofday. Although strictly speaking users should tolerate this behavior because a superuser can always change the clock back, this is a quality of implementation issue and users naturally expect Git to issue timestamps in increasing order unless the superuser has fiddled with the system clock. This patch always uses gettimeofday(...) instead of time(...), and I have verified that the resulting .o files never refer to the name 'time'. A trickier patch would change only those calls for which timestamp monotonicity is user-visible. Such a patch would require more expertise about Git internals, though, and would be harder to maintain later. Another possibility would be to change Git's documentation to warn users that Git does not always issue timestamps in increasing order. However, Git users would likely be either dismayed by this possibility, or confused by the level of detail that any such documentation would require. Yet another possibility would be to fix the Linux kernel so that the time syscall is consistent with the other timestamp syscalls. I suppose this has not been done due to performance implications. (Git's use of timestamps is rare enough that performance is not a significant consideration for git.) However, this wouldn't fix Git's problem on older Linux kernels, or on AIX or MS-Windows. Signed-off-by: Paul Eggert <eggert@cs.ucla.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>
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