git: cf1c35c92e01 - stable/12 - time(3): Refine history in the manual page
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Date: Thu, 21 Apr 2022 06:27:44 UTC
The branch stable/12 has been updated by gbe (doc committer): URL: https://cgit.FreeBSD.org/src/commit/?id=cf1c35c92e01384614a64ea9a66ba6d08121a4f6 commit cf1c35c92e01384614a64ea9a66ba6d08121a4f6 Author: Gordon Bergling <gbe@FreeBSD.org> AuthorDate: 2022-04-14 08:04:14 +0000 Commit: Gordon Bergling <gbe@FreeBSD.org> CommitDate: 2022-04-21 06:27:29 +0000 time(3): Refine history in the manual page The time() system call first appeared in Version 1 AT&T UNIX. Through the Version 3 AT&T UNIX, it returned 60 Hz ticks since an epoch that changed occasionally, because it was a 32-bit value that overflowed in a little over 2 years. In Version 4 AT&T UNIX the granularity of the return value was reduced to whole seconds, delaying the aforementioned overflow until 2038. Version 7 AT&T UNIX introduced the ftime() system call, which returned time at a millisecond level, though retained the gtime() system call (exposed as time() in userland). time() could have been implemented as a wrapper around ftime(), but that wasn't done. 4.1cBSD implemented a higher-precision time function gettimeofday() to replace ftime() and reimplemented time() in terms of that. Since FreeBSD 9 the implementation of time() uses clock_gettime(CLOCK_SECOND) instead of gettimeofday() for performance reasons. With most valuable input from Warner (imp@). Reviewed by: 0mp, jilles, imp Differential Revision: https://reviews.freebsd.org/D34751 (cherry picked from commit 3e0f3678eca7c3f296b9f702992737356f1792da) --- lib/libc/gen/time.3 | 57 +++++++++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 49 insertions(+), 8 deletions(-) diff --git a/lib/libc/gen/time.3 b/lib/libc/gen/time.3 index 1563e672b3ba..52785057a56b 100644 --- a/lib/libc/gen/time.3 +++ b/lib/libc/gen/time.3 @@ -32,7 +32,7 @@ .\" @(#)time.3 8.1 (Berkeley) 6/4/93 .\" $FreeBSD$ .\" -.Dd March 4, 2022 +.Dd April 14, 2022 .Dt TIME 3 .Os .Sh NAME @@ -49,7 +49,7 @@ The .Fn time function returns the value of time in seconds since 0 hours, 0 minutes, -0 seconds, January 1, 1970, Coordinated Universal Time. +0 seconds, January 1, 1970, Coordinated Universal Time (UTC). If an error occurs, .Fn time returns the value @@ -73,12 +73,54 @@ function may fail for any of the reasons described in The .Nm function conforms to -.St -p1003.1-2001 . +.St -p1003.1-2008 . .Sh HISTORY -A +The +.Fn time +system call first appeared in +.At v1 . +Through the +.At v3 , +it returned 60 Hz ticks since an epoch that changed occasionally, because it +was a 32-bit value that overflowed in a little over 2 years. +.Pp +In +.At v4 +the granularity of the return value was reduced to whole seconds, +delaying the aforementioned overflow until 2038. +.Pp +.At v7 +introduced the +.Fn ftime +system call, which returned time at a millisecond level, +though retained the +.Fn gtime +system call (exposed as +.Fn time +in userland). +.Fn time +could have been implemented as a wrapper around +.Fn ftime , +but that wasn't done. +.Pp +.Bx 4.1c +implemented a higher-precision time function +.Fn gettimeofday +to replace +.Fn ftime +and reimplemented +.Fn time +in terms of that. +.Pp +Since +.Fx 9 +the implementation of .Fn time -function appeared in -.At v6 . +uses +.Fn clock_gettime "CLOCK_SECOND" +instead of +.Fn gettimeofday +for performance reasons. .Sh BUGS Neither .St -isoC-99 @@ -92,8 +134,7 @@ on failure; thus, it is impossible for an application to distinguish the valid time value \-1 (representing the last UTC second of 1969) from the error return value. .Pp -Systems conforming to earlier versions of the C and -.Tn POSIX +Systems conforming to earlier versions of the C and POSIX standards (including older versions of .Fx ) did not set