1# semaphore.m4 serial 1
2dnl Copyright (C) 2019-2021 Free Software Foundation, Inc.
3dnl This file is free software; the Free Software Foundation
4dnl gives unlimited permission to copy and/or distribute it,
5dnl with or without modifications, as long as this notice is preserved.
6
7# Sets LIB_SEMAPHORE to the library needed, in addition to $(LIBMULTITHREAD),
8# for getting the <semaphore.h> functions.
9
10AC_DEFUN([gl_SEMAPHORE],
11[
12  AC_REQUIRE([gl_THREADLIB])
13  dnl sem_post is
14  dnl   - in libc on macOS, FreeBSD, AIX, IRIX, Solaris 11, Haiku, Cygwin,
15  dnl   - in libpthread on glibc systems, OpenBSD,
16  dnl   - in libpthread or librt on NetBSD,
17  dnl   - in librt on HP-UX 11, OSF/1, Solaris 10.
18  dnl On the platforms where -lpthread is needed, it is contained in
19  dnl $LIBMULTITHREAD. Therefore, the only library we need to test for is -lrt.
20  AC_CACHE_CHECK([for library needed for semaphore functions],
21    [gl_cv_semaphore_lib],
22    [save_LIBS="$LIBS"
23     LIBS="$LIBS $LIBMULTITHREAD"
24     AC_LINK_IFELSE(
25       [AC_LANG_PROGRAM(
26          [[#include <semaphore.h>]],
27          [[sem_post ((sem_t *)0);]])],
28       [gl_cv_semaphore_lib=none],
29       [LIBS="$LIBS -lrt"
30        AC_LINK_IFELSE(
31          [AC_LANG_PROGRAM(
32             [[#include <semaphore.h>]],
33             [[sem_post ((sem_t *)0);]])],
34          [gl_cv_semaphore_lib='-lrt'],
35          [gl_cv_semaphore_lib=none])
36       ])
37     LIBS="$save_LIBS"
38    ])
39  if test "x$gl_cv_semaphore_lib" = xnone; then
40    LIB_SEMAPHORE=
41  else
42    LIB_SEMAPHORE="$gl_cv_semaphore_lib"
43  fi
44  AC_SUBST([LIB_SEMAPHORE])
45])
46