# select.m4 serial 11

dnl Copyright (C) 2009-2020 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.

AC_DEFUN([gl_FUNC_SELECT],

[

  AC_REQUIRE([gl_HEADER_SYS_SELECT])

  AC_REQUIRE([AC_C_RESTRICT])

  AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles

  AC_REQUIRE([gl_SOCKETS])

  if test "$ac_cv_header_winsock2_h" = yes; then

    REPLACE_SELECT=1

  else

    dnl On Interix 3.5, select(0, NULL, NULL, NULL, timeout) fails with error

    dnl EFAULT.

    AC_CHECK_HEADERS_ONCE([sys/select.h])

    AC_CACHE_CHECK([whether select supports a 0 argument],

      [gl_cv_func_select_supports0],

      [

        AC_RUN_IFELSE([AC_LANG_SOURCE([[

#include <sys/types.h>

#include <sys/time.h>

#if HAVE_SYS_SELECT_H

#include <sys/select.h>

#endif

int main ()

{

  struct timeval timeout;

  timeout.tv_sec = 0;

  timeout.tv_usec = 5;

  return select (0, (fd_set *)0, (fd_set *)0, (fd_set *)0, &timeout) < 0;

}]])], [gl_cv_func_select_supports0=yes], [gl_cv_func_select_supports0=no],

          [

changequote(,)dnl

           case "$host_os" in

                       # Guess no on Interix.

             interix*) gl_cv_func_select_supports0="guessing no";;

                       # Guess yes otherwise.

             *)        gl_cv_func_select_supports0="guessing yes";;

           esac

changequote([,])dnl

          ])

      ])

    case "$gl_cv_func_select_supports0" in

      *yes) ;;

      *) REPLACE_SELECT=1 ;;

    esac

    dnl On FreeBSD 8.2, select() doesn't always reject bad fds.

    AC_CACHE_CHECK([whether select detects invalid fds],

      [gl_cv_func_select_detects_ebadf],

      [

        AC_RUN_IFELSE([AC_LANG_PROGRAM([[

#include <sys/types.h>

#include <sys/time.h>

#if HAVE_SYS_SELECT_H

# include <sys/select.h>

#endif

#include <unistd.h>

#include <errno.h>

]],[[

  fd_set set;

  dup2(0, 16);

  FD_ZERO(&set);

  FD_SET(16, &set);

  close(16);

  struct timeval timeout;

  timeout.tv_sec = 0;

  timeout.tv_usec = 5;

  return select (17, &set, NULL, NULL, &timeout) != -1 || errno != EBADF;

]])], [gl_cv_func_select_detects_ebadf=yes],

      [gl_cv_func_select_detects_ebadf=no],

          [

           case "$host_os" in

                             # Guess yes on Linux systems.

            linux-* | linux) gl_cv_func_select_detects_ebadf="guessing yes" ;;

                             # Guess yes on glibc systems.

            *-gnu* | gnu*)   gl_cv_func_select_detects_ebadf="guessing yes" ;;

                             # If we don't know, obey --enable-cross-guesses.

            *)               gl_cv_func_select_detects_ebadf="$gl_cross_guess_normal" ;;

           esac

          ])

      ])

    case $gl_cv_func_select_detects_ebadf in

      *yes) ;;

      *) REPLACE_SELECT=1 ;;

    esac

  fi

  dnl Determine the needed libraries.

  LIB_SELECT="$LIBSOCKET"

  if test $REPLACE_SELECT = 1; then

    case "$host_os" in

      mingw*)

        dnl On the MSVC platform, the function MsgWaitForMultipleObjects

        dnl (used in lib/select.c) requires linking with -luser32. On mingw,

        dnl it is implicit.

        AC_LINK_IFELSE(

          [AC_LANG_SOURCE([[

#define WIN32_LEAN_AND_MEAN

#include <windows.h>

int

main ()

{

  MsgWaitForMultipleObjects (0, NULL, 0, 0, 0);

  return 0;

}]])],

          [],

          [LIB_SELECT="$LIB_SELECT -luser32"])

        ;;

    esac

  fi

  AC_SUBST([LIB_SELECT])

])