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gnulib/m4/pthread_sigmask.m4
Paul Eggert 87fb310b69 doc: be more like POSIX in threading terms 
In documentation and comments, be more like POSIX in terminology
involving multithreading.  Explain the distinction between
multithreaded process vs multithreaded program.  Change “program”
to “process” when the latter wording is more accurate or informative.
Simplify the wording for the constraints on processes that use
unlocked I/O.  Change “multithread-safe” to “thread-safe”.
Change “thread-safety” to “thread safety”.
However, do not change “multithreaded” to “multi-threaded” even
though there are some uses of both spellinga, as there are a whole
bunch of uses of “multithreaded”, also in identifier names;
perhaps Gnulib should even standardize on “multithreaded”
(not “multi-threaded”), contra POSIX.
2026-04-11 13:21:19 -07:00

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# pthread_sigmask.m4
# serial 26
dnl Copyright (C) 2011-2026 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
dnl with or without modifications, as long as this notice is preserved.
dnl This file is offered as-is, without any warranty.
AC_DEFUN([gl_FUNC_PTHREAD_SIGMASK],
[
AC_REQUIRE([gl_SIGNAL_H_DEFAULTS])
AC_CHECK_FUNCS_ONCE([pthread_sigmask])
dnl On MinGW pthread_sigmask is just a macro which always returns 0.
dnl It does not exist as a real function, which is required by POSIX.
AC_CACHE_CHECK([whether pthread_sigmask is a macro],
[gl_cv_func_pthread_sigmask_macro],
[AC_EGREP_CPP([headers_define_pthread_sigmask], [
#include <pthread.h>
#include <signal.h>
#if defined _WIN32 && defined pthread_sigmask
headers_define_pthread_sigmask
#endif],
[gl_cv_func_pthread_sigmask_macro=yes],
[gl_cv_func_pthread_sigmask_macro=no])
])
PTHREAD_SIGMASK_LIB=
if test $gl_cv_func_pthread_sigmask_macro = yes; then
dnl pthread_sigmask is a dummy macro.
HAVE_PTHREAD_SIGMASK=0
dnl Make sure to '#undef pthread_sigmask' before defining it.
REPLACE_PTHREAD_SIGMASK=1
else
dnl Test whether the gnulib module 'threadlib' is in use.
dnl Some packages like Emacs use --avoid=threadlib.
dnl Write the symbol in such a way that it does not cause 'aclocal' to pick
dnl the threadlib.m4 file that is installed in $PREFIX/share/aclocal/.
m4_ifdef([gl_][THREADLIB], [
AC_REQUIRE([gl_][THREADLIB])
if test "$gl_threads_api" = posix; then
if test $ac_cv_func_pthread_sigmask = yes; then
dnl pthread_sigmask is available without -lpthread.
:
else
if test -n "$LIBMULTITHREAD"; then
AC_CACHE_CHECK([for pthread_sigmask in $LIBMULTITHREAD],
[gl_cv_func_pthread_sigmask_in_LIBMULTITHREAD],
[gl_saved_LIBS="$LIBS"
LIBS="$LIBS $LIBMULTITHREAD"
AC_LINK_IFELSE(
[AC_LANG_PROGRAM(
[[#include <pthread.h>
#include <signal.h>
]],
[[return pthread_sigmask (0, (sigset_t *) 0, (sigset_t *) 0);]])
],
[gl_cv_func_pthread_sigmask_in_LIBMULTITHREAD=yes],
[gl_cv_func_pthread_sigmask_in_LIBMULTITHREAD=no])
LIBS="$gl_saved_LIBS"
])
if test $gl_cv_func_pthread_sigmask_in_LIBMULTITHREAD = yes; then
dnl pthread_sigmask is available with -pthread or -lpthread.
PTHREAD_SIGMASK_LIB="$LIBMULTITHREAD"
else
dnl pthread_sigmask is not available at all.
HAVE_PTHREAD_SIGMASK=0
fi
else
dnl pthread_sigmask is not available at all.
HAVE_PTHREAD_SIGMASK=0
fi
fi
else
dnl pthread_sigmask may exist but does not interoperate with the chosen
dnl multithreading facility.
if test $ac_cv_func_pthread_sigmask = yes; then
REPLACE_PTHREAD_SIGMASK=1
else
HAVE_PTHREAD_SIGMASK=0
fi
fi
], [
dnl The module 'threadlib' is not in use, due to --avoid=threadlib being
dnl specified.
dnl The package either has prepared CPPFLAGS and LIBS for use of
dnl POSIX:2008 threads, or wants to build single-threaded programs.
if test $ac_cv_func_pthread_sigmask = yes; then
dnl pthread_sigmask exists and does not require extra libraries.
dnl Assume that it is declared.
:
else
dnl pthread_sigmask either does not exist or needs extra libraries.
HAVE_PTHREAD_SIGMASK=0
dnl Define the symbol rpl_pthread_sigmask, not pthread_sigmask,
dnl so as to not accidentally override the system's pthread_sigmask
dnl symbol from libpthread.
REPLACE_PTHREAD_SIGMASK=1
fi
])
fi
dnl We want to be able to use pthread_sigmask as a thread-safe
dnl replacement of sigprocmask, in both single-threaded and multithreaded
dnl processes. Therefore enforce PTHREAD_SIGMASK_LIB to be empty, whenever
dnl possible.
if test -n "$PTHREAD_SIGMASK_LIB"; then
dnl We get here on glibc ≤ 2.31, NetBSD, OpenBSD ≤ 5.8, AIX.
dnl Except on AIX, pthread_sigmask and sigprocmask are equivalent.
dnl Whereas on AIX, sigprocmask is not allowed in multithreaded processes
dnl <https://www.ibm.com/docs/en/aix/7.2.0?topic=s-sigprocmask-sigsetmask-sigblock-subroutine>.
AC_REQUIRE([AC_CANONICAL_HOST])
case "$host_os" in
aix*) ;;
*)
REPLACE_PTHREAD_SIGMASK=1
AC_DEFINE([PTHREAD_SIGMASK_NOT_IN_LIBC], [1],
[Define to 1 if pthread_sigmask requires linking with some library.])
PTHREAD_SIGMASK_LIB=
;;
esac
fi
AC_SUBST([PTHREAD_SIGMASK_LIB])
dnl For backward compatibility.
LIB_PTHREAD_SIGMASK="$PTHREAD_SIGMASK_LIB"
AC_SUBST([LIB_PTHREAD_SIGMASK])
dnl We don't need a variable LTLIB_PTHREAD_SIGMASK, because when
dnl "$gl_threads_api" = posix, $LTLIBMULTITHREAD and $LIBMULTITHREAD are the
dnl same.
dnl Now test for some bugs in the system function.
if test $HAVE_PTHREAD_SIGMASK = 1; then
AC_REQUIRE([AC_PROG_CC])
AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
dnl On FreeBSD 13.0, MidnightBSD 1.1, HP-UX 11.31, Solaris 9, in programs
dnl that are not linked with -lpthread, the pthread_sigmask() function
dnl always returns 0 and has no effect.
if test -z "$PTHREAD_SIGMASK_LIB"; then
case " $LIBS " in
*' -pthread '*) ;;
*' -lpthread '*) ;;
*)
AC_CACHE_CHECK([whether pthread_sigmask works without -lpthread],
[gl_cv_func_pthread_sigmask_in_libc_works],
[
AC_RUN_IFELSE(
[AC_LANG_SOURCE([[
#include <pthread.h>
#include <signal.h>
#include <stddef.h>
int main ()
{
sigset_t set;
sigemptyset (&set);
return pthread_sigmask (1729, &set, NULL) != 0;
}]])],
[gl_cv_func_pthread_sigmask_in_libc_works=no],
[gl_cv_func_pthread_sigmask_in_libc_works=yes],
[
changequote(,)dnl
case "$host_os" in
freebsd* | midnightbsd* | hpux* | solaris | solaris2.[2-9]*)
gl_cv_func_pthread_sigmask_in_libc_works="guessing no";;
*)
gl_cv_func_pthread_sigmask_in_libc_works="guessing yes";;
esac
changequote([,])dnl
])
])
case "$gl_cv_func_pthread_sigmask_in_libc_works" in
*no)
REPLACE_PTHREAD_SIGMASK=1
AC_DEFINE([PTHREAD_SIGMASK_INEFFECTIVE], [1],
[Define to 1 if pthread_sigmask may return 0 and have no effect.])
;;
esac;;
esac
fi
dnl On Cygwin 1.7.5, the pthread_sigmask() has a wrong return value
dnl convention: Upon failure, it returns -1 and sets errno.
dnl Likewise on NetBSD 9.3, when libpthread is not in use; see
dnl https://gnats.netbsd.org/cgi-bin/query-pr-single.pl?number=57214 .
AC_CACHE_CHECK([whether pthread_sigmask returns error numbers],
[gl_cv_func_pthread_sigmask_return_works],
[
gl_saved_LIBS="$LIBS"
LIBS="$LIBS $PTHREAD_SIGMASK_LIB"
AC_RUN_IFELSE(
[AC_LANG_SOURCE([[
#include <pthread.h>
#include <signal.h>
#include <stddef.h>
int main ()
{
sigset_t set;
sigemptyset (&set);
if (pthread_sigmask (1729, &set, NULL) == -1)
return 1;
return 0;
}]])],
[gl_cv_func_pthread_sigmask_return_works=yes],
[gl_cv_func_pthread_sigmask_return_works=no],
[case "$host_os" in
cygwin*)
gl_cv_func_pthread_sigmask_return_works="guessing no";;
*)
gl_cv_func_pthread_sigmask_return_works="guessing yes";;
esac
])
LIBS="$gl_saved_LIBS"
])
case "$gl_cv_func_pthread_sigmask_return_works" in
*no)
REPLACE_PTHREAD_SIGMASK=1
AC_DEFINE([PTHREAD_SIGMASK_FAILS_WITH_ERRNO], [1],
[Define to 1 if pthread_sigmask(), when it fails, returns -1 and sets errno.])
;;
esac
fi
])
# Prerequisite of lib/pthread_sigmask.c.
AC_DEFUN([gl_PREREQ_PTHREAD_SIGMASK],
[
if test $HAVE_PTHREAD_SIGMASK = 1; then
AC_DEFINE([HAVE_PTHREAD_SIGMASK], [1],
[Define to 1 if the pthread_sigmask function can be used (despite bugs).])
fi
])
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