Ted Unangst wrote on Tue, Jul 22, 2025 at 12:58:57AM -0400:

> Another go at this.

OK schwarze@ if you fix the one remaining issue shown inline below.

Yours,
  Ingo

> 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: flockfile.3
> ===================================================================
> RCS file: flockfile.3
> diff -N flockfile.3
> --- /dev/null	1 Jan 1970 00:00:00 -0000
> +++ flockfile.3	11 Jul 2025 03:56:12 -0000
> @@ -0,0 +1,74 @@
> +.\" $OpenBSD$
> +.\"
> +.\" Copyright (c) 2025 Ted Unangst <tedu@openbsd.org>
> +.\"
> +.\" 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
> +and
> +.Fn ftrylockfile
> +increment the lock count associated with
> +.Fa file
> +on behalf of the calling thread.
> +If another thread owns the lock,
> +.Fn flockfile
> +blocks until the lock becomes available, whereas
> +.Fn ftrylockfile
> +returns immediately and indicates failure.
> +.Pp
> +When called by a thread holding the lock,
> +.Fn funlockfile
> +decrements the lock count by one.
> +When the lock count reaches zero, the calling thread relinquishes
> +ownership of the lock.
> +.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 SEE ALSO
> +.Xr getc_unlocked 3 ,
> +.Xr putc_unlocked 3 ,
> +.Xr pthreads 3

The order must be:

.Xr getc_unlocked 3 ,
.Xr pthreads 3 ,
.Xr putc_unlocked 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: 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	11 Jul 2025 03:59:35 -0000
> @@ -38,6 +38,8 @@
>  .Nm fgetc ,
>  .Nm getc ,
>  .Nm getchar ,
> +.Nm getc_unlocked ,
> +.Nm getchar_unlocked ,
>  .Nm getw
>  .Nd get next character or word from input stream
>  .Sh SYNOPSIS
> @@ -49,6 +51,10 @@
>  .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 +79,15 @@ 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
> +for thread safe operation.
> +.Pp
> +The
>  .Fn getw
>  function obtains the next
>  .Vt int
> @@ -99,6 +114,7 @@ until the condition is cleared with
>  .Xr clearerr 3 .
>  .Sh SEE ALSO
>  .Xr ferror 3 ,
> +.Xr flockfile 3 ,
>  .Xr fopen 3 ,
>  .Xr fread 3 ,
>  .Xr getwc 3 ,
> @@ -112,6 +128,12 @@ and
>  .Fn getchar
>  functions conform to
>  .St -ansiC .
> +The
> +.Fn getc_unlocked
> +and
> +.Fn getchar_unlocked
> +functions conform to
> +.St -p1003.1-2024 .
>  .Sh HISTORY
>  The
>  .Fn getc
> @@ -126,6 +148,12 @@ and
>  .Fn fgetc
>  in
>  .At v7 .
> +The
> +.Fn getc_unlocked
> +and
> +.Fn getchar_unlocked
> +functions have been available since
> +.Ox 2.5 .
>  .Sh BUGS
>  Since
>  .Dv EOF
> 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	11 Jul 2025 03:59:50 -0000
> @@ -38,6 +38,8 @@
>  .Nm fputc ,
>  .Nm putc ,
>  .Nm putchar ,
> +.Nm putc_unlocked ,
> +.Nm putchar_unlocked ,
>  .Nm putw
>  .Nd output a character or word to a stream
>  .Sh SYNOPSIS
> @@ -49,6 +51,10 @@
>  .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 +83,15 @@ 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
> +for thread safe operation.
> +.Pp
> +The
>  .Fn putw
>  function writes the specified
>  .Vt int
> @@ -115,6 +130,7 @@ or
>  .Xr realloc 3 .
>  .Sh SEE ALSO
>  .Xr ferror 3 ,
> +.Xr flockfile 3 ,
>  .Xr fopen 3 ,
>  .Xr getc 3 ,
>  .Xr putwc 3 ,
> @@ -127,6 +143,12 @@ and
>  .Fn putchar ,
>  conform to
>  .St -ansiC .
> +The
> +.Fn putc_unlocked
> +and
> +.Fn putchar_unlocked
> +functions conform to
> +.St -p1003.1-2024 .
>  .Sh HISTORY
>  The
>  .Fn putc
> @@ -141,6 +163,12 @@ and
>  .Fn fputc
>  in
>  .At v7 .
> +The
> +.Fn putc_unlocked
> +and
> +.Fn putchar_unlocked
> +functions have been available since
> +.Ox 2.5 .
>  .Sh BUGS
>  Since the size and byte order of an
>  .Vt int