From: "Ted Unangst" Subject: flockfile.3 To: tech@openbsd.org Date: Tue, 08 Jul 2025 23:30:44 -0400 Here's a new man page for flockfile.3 to be placed in libc/stdio. Also, a diff for the getc.3 and putc.3 for the unlocked functions. .\" $OpenBSD$ .\" .\" Copyright (c) 2025 Ted Unangst .\" .\" Permission to use, copy, modify, and distribute this software for any .\" purpose with or without fee is hereby granted, provided that the above .\" copyright notice and this permission notice appear in all copies. .\" .\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES .\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF .\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR .\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES .\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. .\" .Dd $Mdocdate$ .Dt FLOCKFILE 3 .Os .Sh NAME .Nm flockfile , .Nm ftrylockfile , .Nm funlockfile .Nd locking for stdio streams .Sh SYNOPSIS .In stdio.h .Ft void .Fn flockfile "FILE *file" .Ft int .Fn ftrylockfile "FILE *file" .Ft void .Fn funlockfile "FILE *file" .Sh DESCRIPTION These functions provide application control over the locking of stdio streams. .Fn flockfile increments the lock count associated with .Fa file , blocking until the lock is available. .Fn ftrylockfile does the same but will not block if another thread owns the lock. .Pp .Fn funlockfile decrements the lock count by one. .Pp Functions such as .Xr fread 3 and .Xr fprintf 3 are internally thread safe by default, but additional locking may be used to coordinate sequences of multiple calls. .Sh RETURN VALUES .Fn ftrylockfile returns zero for success and non-zero for failure. .Sh ERRORS None. .Sh SEE ALSO .Xr getc_unlocked , .Xr putc_unlocked , .Xr pthreads 3 .Sh STANDARDS These functions conform to .St -p1003.1-2024 . .Sh HISTORY These functions have been available since .Ox 2.5 . .Sh CAVEATS Reading from one stream can flush a different buffered output stream, leading to deadlocks. Index: Makefile.inc =================================================================== RCS file: /home/cvs/src/lib/libc/stdio/Makefile.inc,v diff -u -p -r1.31 Makefile.inc --- Makefile.inc 12 Aug 2024 20:56:55 -0000 1.31 +++ Makefile.inc 9 Jul 2025 03:14:10 -0000 @@ -22,7 +22,8 @@ SRCS+= asprintf.c clrerr.c fclose.c fdop getdelim.c getline.c dprintf.c vdprintf.c \ fpending.c freadahead.c freading.c freadptr.c fseterr.c fwriting.c -MAN+= fclose.3 ferror.3 fflush.3 fgetln.3 fgets.3 fgetwln.3 fmemopen.3 \ +MAN+= fclose.3 ferror.3 fflush.3 fgetln.3 fgets.3 fgetwln.3 \ + flockfile.3 fmemopen.3 \ fopen.3 __fpending.3 fputs.3 fread.3 fseek.3 funopen.3 getc.3 \ open_memstream.3 perror.3 printf.3 putc.3 remove.3 scanf.3 setbuf.3 \ setvbuf.3 stdio.3 tmpnam.3 ungetc.3 fgetws.3 fputws.3 fwide.3 getwc.3 \ Index: getc.3 =================================================================== RCS file: /home/cvs/src/lib/libc/stdio/getc.3,v diff -u -p -r1.17 getc.3 --- getc.3 28 Sep 2023 01:51:00 -0000 1.17 +++ getc.3 9 Jul 2025 03:25:14 -0000 @@ -49,6 +49,10 @@ .Ft int .Fn getchar "void" .Ft int +.Fn getc_unlocked "FILE *stream" +.Ft int +.Fn getchar_unlocked "void" +.Ft int .Fn getw "FILE *stream" .Sh DESCRIPTION The @@ -73,6 +77,14 @@ with the argument .Em stdin . .Pp The +.Fn getc_unlocked +and +.Fn getchar_unlocked +functions perform the same action, but do not obtain the stream lock. +They require that the stream first be locked with +.Xr flockfile 3 . +.Pp +The .Fn getw function obtains the next .Vt int @@ -99,6 +111,7 @@ until the condition is cleared with .Xr clearerr 3 . .Sh SEE ALSO .Xr ferror 3 , +.Xr flockfile , .Xr fopen 3 , .Xr fread 3 , .Xr getwc 3 , @@ -112,6 +125,12 @@ and .Fn getchar functions conform to .St -ansiC . +The +.Fn getc_unlocked +and +.Fn getchar_unlocked +conform to +.St -p1003.1-2024 . .Sh HISTORY The .Fn getc Index: putc.3 =================================================================== RCS file: /home/cvs/src/lib/libc/stdio/putc.3,v diff -u -p -r1.14 putc.3 --- putc.3 11 Sep 2022 06:38:11 -0000 1.14 +++ putc.3 9 Jul 2025 03:24:34 -0000 @@ -49,6 +49,10 @@ .Ft int .Fn putchar "int c" .Ft int +.Fn putc_unlocked "int c" "FILE *stream" +.Ft int +.Fn putchar_unlocked "int c" +.Ft int .Fn putw "int w" "FILE *stream" .Sh DESCRIPTION The @@ -77,6 +81,14 @@ with an output stream of .Em stdout . .Pp The +.Fn putc_unlocked +and +.Fn putchar_unlocked +functions perform the same action, but do not obtain the stream lock. +They require that the stream first be locked with +.Xr flockfile 3 . +.Pp +The .Fn putw function writes the specified .Vt int @@ -115,6 +127,7 @@ or .Xr realloc 3 . .Sh SEE ALSO .Xr ferror 3 , +.Xr flockfile , .Xr fopen 3 , .Xr getc 3 , .Xr putwc 3 , @@ -127,6 +140,12 @@ and .Fn putchar , conform to .St -ansiC . +The +.Fn putc_unlocked +and +.Fn putchar_unlocked +conform to +.St -p1003.1-2024 . .Sh HISTORY The .Fn putc