1 files changed, 45 insertions, 0 deletions
diff --git a/m4/semaphore.m4 b/m4/semaphore.m4
new file mode 100644
index 0000000..ca20c76
--- /dev/null
+++ b/m4/semaphore.m4
@@ -0,0 +1,45 @@
+# semaphore.m4 serial 1
+dnl Copyright (C) 2019-2020 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.
+
+# Sets LIB_SEMAPHORE to the library needed, in addition to $(LIBMULTITHREAD),
+# for getting the <semaphore.h> functions.
+
+AC_DEFUN([gl_SEMAPHORE],
+[
+  AC_REQUIRE([gl_THREADLIB])
+  dnl sem_post is
+  dnl   - in libc on macOS, FreeBSD, AIX, IRIX, Solaris 11, Haiku, Cygwin,
+  dnl   - in libpthread on glibc systems, OpenBSD,
+  dnl   - in libpthread or librt on NetBSD,
+  dnl   - in librt on HP-UX 11, OSF/1, Solaris 10.
+  dnl On the platforms where -lpthread is needed, it is contained in
+  dnl $LIBMULTITHREAD. Therefore, the only library we need to test for is -lrt.
+  AC_CACHE_CHECK([for library needed for semaphore functions],
+    [gl_cv_semaphore_lib],
+    [save_LIBS="$LIBS"
+     LIBS="$LIBS $LIBMULTITHREAD"
+     AC_LINK_IFELSE(
+       [AC_LANG_PROGRAM(
+          [[#include <semaphore.h>]],
+          [[sem_post ((sem_t *)0);]])],
+       [gl_cv_semaphore_lib=none],
+       [LIBS="$LIBS -lrt"
+        AC_LINK_IFELSE(
+          [AC_LANG_PROGRAM(
+             [[#include <semaphore.h>]],
+             [[sem_post ((sem_t *)0);]])],
+          [gl_cv_semaphore_lib='-lrt'],
+          [gl_cv_semaphore_lib=none])
+       ])
+     LIBS="$save_LIBS"
+    ])
+  if test "x$gl_cv_semaphore_lib" = xnone; then
+    LIB_SEMAPHORE=
+  else
+    LIB_SEMAPHORE="$gl_cv_semaphore_lib"
+  fi
+  AC_SUBST([LIB_SEMAPHORE])
+])