m4/ax_pthread.m4 - third_party/protobuf - Git at Google

 # ===========================================================================
 #        https://www.gnu.org/software/autoconf-archive/ax_pthread.html
 # ===========================================================================
 #
 # SYNOPSIS
 #
 #   AX_PTHREAD([ACTION-IF-FOUND[, ACTION-IF-NOT-FOUND]])
 #
 # DESCRIPTION
 #
 #   This macro figures out how to build C programs using POSIX threads. It
 #   sets the PTHREAD_LIBS output variable to the threads library and linker
 #   flags, and the PTHREAD_CFLAGS output variable to any special C compiler
 #   flags that are needed. (The user can also force certain compiler
 #   flags/libs to be tested by setting these environment variables.)
 #
 #   Also sets PTHREAD_CC to any special C compiler that is needed for
 #   multi-threaded programs (defaults to the value of CC otherwise). (This
 #   is necessary on AIX to use the special cc_r compiler alias.)
 #
 #   NOTE: You are assumed to not only compile your program with these flags,
 #   but also to link with them as well. For example, you might link with
 #   $PTHREAD_CC $CFLAGS $PTHREAD_CFLAGS $LDFLAGS ... $PTHREAD_LIBS $LIBS
 #
 #   If you are only building threaded programs, you may wish to use these
 #   variables in your default LIBS, CFLAGS, and CC:
 #
 #     LIBS="$PTHREAD_LIBS $LIBS"
 #     CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
 #     CC="$PTHREAD_CC"
 #
 #   In addition, if the PTHREAD_CREATE_JOINABLE thread-attribute constant
 #   has a nonstandard name, this macro defines PTHREAD_CREATE_JOINABLE to
 #   that name (e.g. PTHREAD_CREATE_UNDETACHED on AIX).
 #
 #   Also HAVE_PTHREAD_PRIO_INHERIT is defined if pthread is found and the
 #   PTHREAD_PRIO_INHERIT symbol is defined when compiling with
 #   PTHREAD_CFLAGS.
 #
 #   ACTION-IF-FOUND is a list of shell commands to run if a threads library
 #   is found, and ACTION-IF-NOT-FOUND is a list of commands to run it if it
 #   is not found. If ACTION-IF-FOUND is not specified, the default action
 #   will define HAVE_PTHREAD.
 #
 #   Please let the authors know if this macro fails on any platform, or if
 #   you have any other suggestions or comments. This macro was based on work
 #   by SGJ on autoconf scripts for FFTW (http://www.fftw.org/) (with help
 #   from M. Frigo), as well as ac_pthread and hb_pthread macros posted by
 #   Alejandro Forero Cuervo to the autoconf macro repository. We are also
 #   grateful for the helpful feedback of numerous users.
 #
 #   Updated for Autoconf 2.68 by Daniel Richard G.
 #
 # LICENSE
 #
 #   Copyright (c) 2008 Steven G. Johnson <stevenj@alum.mit.edu>
 #   Copyright (c) 2011 Daniel Richard G. <skunk@iSKUNK.ORG>
 #   Copyright (c) 2019 Marc Stevens <marc.stevens@cwi.nl>
 #
 #   This program is free software: you can redistribute it and/or modify it
 #   under the terms of the GNU General Public License as published by the
 #   Free Software Foundation, either version 3 of the License, or (at your
 #   option) any later version.
 #
 #   This program is distributed in the hope that it will be useful, but
 #   WITHOUT ANY WARRANTY; without even the implied warranty of
 #   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
 #   Public License for more details.
 #
 #   You should have received a copy of the GNU General Public License along
 #   with this program. If not, see <https://www.gnu.org/licenses/>.
 #
 #   As a special exception, the respective Autoconf Macro's copyright owner
 #   gives unlimited permission to copy, distribute and modify the configure
 #   scripts that are the output of Autoconf when processing the Macro. You
 #   need not follow the terms of the GNU General Public License when using
 #   or distributing such scripts, even though portions of the text of the
 #   Macro appear in them. The GNU General Public License (GPL) does govern
 #   all other use of the material that constitutes the Autoconf Macro.
 #
 #   This special exception to the GPL applies to versions of the Autoconf
 #   Macro released by the Autoconf Archive. When you make and distribute a
 #   modified version of the Autoconf Macro, you may extend this special
 #   exception to the GPL to apply to your modified version as well.

 #serial 27

 AU_ALIAS([ACX_PTHREAD], [AX_PTHREAD])
 AC_DEFUN([AX_PTHREAD], [
 AC_REQUIRE([AC_CANONICAL_HOST])
 AC_REQUIRE([AC_PROG_CC])
 AC_REQUIRE([AC_PROG_SED])
 AC_LANG_PUSH([C])
 ax_pthread_ok=no

 # We used to check for pthread.h first, but this fails if pthread.h
 # requires special compiler flags (e.g. on Tru64 or Sequent).
 # It gets checked for in the link test anyway.

 # First of all, check if the user has set any of the PTHREAD_LIBS,
 # etcetera environment variables, and if threads linking works using
 # them:
 if test "x$PTHREAD_CFLAGS$PTHREAD_LIBS" != "x"; then
         ax_pthread_save_CC="$CC"
         ax_pthread_save_CFLAGS="$CFLAGS"
         ax_pthread_save_LIBS="$LIBS"
         AS_IF([test "x$PTHREAD_CC" != "x"], [CC="$PTHREAD_CC"])
         CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
         LIBS="$PTHREAD_LIBS $LIBS"
         AC_MSG_CHECKING([for pthread_join using $CC $PTHREAD_CFLAGS $PTHREAD_LIBS])
         AC_LINK_IFELSE([AC_LANG_CALL([], [pthread_join])], [ax_pthread_ok=yes])
         AC_MSG_RESULT([$ax_pthread_ok])
         if test "x$ax_pthread_ok" = "xno"; then
                 PTHREAD_LIBS=""
                 PTHREAD_CFLAGS=""
         fi
         CC="$ax_pthread_save_CC"
         CFLAGS="$ax_pthread_save_CFLAGS"
         LIBS="$ax_pthread_save_LIBS"
 fi

 # We must check for the threads library under a number of different
 # names; the ordering is very important because some systems
 # (e.g. DEC) have both -lpthread and -lpthreads, where one of the
 # libraries is broken (non-POSIX).

 # Create a list of thread flags to try. Items with a "," contain both
 # C compiler flags (before ",") and linker flags (after ","). Other items
 # starting with a "-" are C compiler flags, and remaining items are
 # library names, except for "none" which indicates that we try without
 # any flags at all, and "pthread-config" which is a program returning
 # the flags for the Pth emulation library.

 ax_pthread_flags="pthreads none -Kthread -pthread -pthreads -mthreads pthread --thread-safe -mt pthread-config"

 # The ordering *is* (sometimes) important.  Some notes on the
 # individual items follow:

 # pthreads: AIX (must check this before -lpthread)
 # none: in case threads are in libc; should be tried before -Kthread and
 #       other compiler flags to prevent continual compiler warnings
 # -Kthread: Sequent (threads in libc, but -Kthread needed for pthread.h)
 # -pthread: Linux/gcc (kernel threads), BSD/gcc (userland threads), Tru64
 #           (Note: HP C rejects this with "bad form for `-t' option")
 # -pthreads: Solaris/gcc (Note: HP C also rejects)
 # -mt: Sun Workshop C (may only link SunOS threads [-lthread], but it
 #      doesn't hurt to check since this sometimes defines pthreads and
 #      -D_REENTRANT too), HP C (must be checked before -lpthread, which
 #      is present but should not be used directly; and before -mthreads,
 #      because the compiler interprets this as "-mt" + "-hreads")
 # -mthreads: Mingw32/gcc, Lynx/gcc
 # pthread: Linux, etcetera
 # --thread-safe: KAI C++
 # pthread-config: use pthread-config program (for GNU Pth library)

 case $host_os in

         freebsd*)

         # -kthread: FreeBSD kernel threads (preferred to -pthread since SMP-able)
         # lthread: LinuxThreads port on FreeBSD (also preferred to -pthread)

         ax_pthread_flags="-kthread lthread $ax_pthread_flags"
         ;;

         hpux*)

         # From the cc(1) man page: "[-mt] Sets various -D flags to enable
         # multi-threading and also sets -lpthread."

         ax_pthread_flags="-mt -pthread pthread $ax_pthread_flags"
         ;;

         openedition*)

         # IBM z/OS requires a feature-test macro to be defined in order to
         # enable POSIX threads at all, so give the user a hint if this is
         # not set. (We don't define these ourselves, as they can affect
         # other portions of the system API in unpredictable ways.)

         AC_EGREP_CPP([AX_PTHREAD_ZOS_MISSING],
             [
 #            if !defined(_OPEN_THREADS) && !defined(_UNIX03_THREADS)
              AX_PTHREAD_ZOS_MISSING
 #            endif
             ],
             [AC_MSG_WARN([IBM z/OS requires -D_OPEN_THREADS or -D_UNIX03_THREADS to enable pthreads support.])])
         ;;

         solaris*)

         # On Solaris (at least, for some versions), libc contains stubbed
         # (non-functional) versions of the pthreads routines, so link-based
         # tests will erroneously succeed. (N.B.: The stubs are missing
         # pthread_cleanup_push, or rather a function called by this macro,
         # so we could check for that, but who knows whether they'll stub
         # that too in a future libc.)  So we'll check first for the
         # standard Solaris way of linking pthreads (-mt -lpthread).

         ax_pthread_flags="-mt,-lpthread pthread $ax_pthread_flags"
         ;;
 esac

 # Are we compiling with Clang?

 AC_CACHE_CHECK([whether $CC is Clang],
     [ax_cv_PTHREAD_CLANG],
     [ax_cv_PTHREAD_CLANG=no
      # Note that Autoconf sets GCC=yes for Clang as well as GCC
      if test "x$GCC" = "xyes"; then
         AC_EGREP_CPP([AX_PTHREAD_CC_IS_CLANG],
             [/* Note: Clang 2.7 lacks __clang_[a-z]+__ */
 #            if defined(__clang__) && defined(__llvm__)
              AX_PTHREAD_CC_IS_CLANG
 #            endif
             ],
             [ax_cv_PTHREAD_CLANG=yes])
      fi
     ])
 ax_pthread_clang="$ax_cv_PTHREAD_CLANG"


 # GCC generally uses -pthread, or -pthreads on some platforms (e.g. SPARC)

 # Note that for GCC and Clang -pthread generally implies -lpthread,
 # except when -nostdlib is passed.
 # This is problematic using libtool to build C++ shared libraries with pthread:
 # [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=25460
 # [2] https://bugzilla.redhat.com/show_bug.cgi?id=661333
 # [3] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=468555
 # To solve this, first try -pthread together with -lpthread for GCC

 AS_IF([test "x$GCC" = "xyes"],
       [ax_pthread_flags="-pthread,-lpthread -pthread -pthreads $ax_pthread_flags"])

 # Clang takes -pthread (never supported any other flag), but we'll try with -lpthread first

 AS_IF([test "x$ax_pthread_clang" = "xyes"],
       [ax_pthread_flags="-pthread,-lpthread -pthread"])


 # The presence of a feature test macro requesting re-entrant function
 # definitions is, on some systems, a strong hint that pthreads support is
 # correctly enabled

 case $host_os in
         darwin* | hpux* | linux* | osf* | solaris*)
         ax_pthread_check_macro="_REENTRANT"
         ;;

         aix*)
         ax_pthread_check_macro="_THREAD_SAFE"
         ;;

         *)
         ax_pthread_check_macro="--"
         ;;
 esac
 AS_IF([test "x$ax_pthread_check_macro" = "x--"],
       [ax_pthread_check_cond=0],
       [ax_pthread_check_cond="!defined($ax_pthread_check_macro)"])


 if test "x$ax_pthread_ok" = "xno"; then
 for ax_pthread_try_flag in $ax_pthread_flags; do

         case $ax_pthread_try_flag in
                 none)
                 AC_MSG_CHECKING([whether pthreads work without any flags])
                 ;;

                 *,*)
                 PTHREAD_CFLAGS=`echo $ax_pthread_try_flag | sed "s/^\(.*\),\(.*\)$/\1/"`
                 PTHREAD_LIBS=`echo $ax_pthread_try_flag | sed "s/^\(.*\),\(.*\)$/\2/"`
                 AC_MSG_CHECKING([whether pthreads work with "$PTHREAD_CFLAGS" and "$PTHREAD_LIBS"])
                 ;;

                 -*)
                 AC_MSG_CHECKING([whether pthreads work with $ax_pthread_try_flag])
                 PTHREAD_CFLAGS="$ax_pthread_try_flag"
                 ;;

                 pthread-config)
                 AC_CHECK_PROG([ax_pthread_config], [pthread-config], [yes], [no])
                 AS_IF([test "x$ax_pthread_config" = "xno"], [continue])
                 PTHREAD_CFLAGS="`pthread-config --cflags`"
                 PTHREAD_LIBS="`pthread-config --ldflags` `pthread-config --libs`"
                 ;;

                 *)
                 AC_MSG_CHECKING([for the pthreads library -l$ax_pthread_try_flag])
                 PTHREAD_LIBS="-l$ax_pthread_try_flag"
                 ;;
         esac

         ax_pthread_save_CFLAGS="$CFLAGS"
         ax_pthread_save_LIBS="$LIBS"
         CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
         LIBS="$PTHREAD_LIBS $LIBS"

         # Check for various functions.  We must include pthread.h,
         # since some functions may be macros.  (On the Sequent, we
         # need a special flag -Kthread to make this header compile.)
         # We check for pthread_join because it is in -lpthread on IRIX
         # while pthread_create is in libc.  We check for pthread_attr_init
         # due to DEC craziness with -lpthreads.  We check for
         # pthread_cleanup_push because it is one of the few pthread
         # functions on Solaris that doesn't have a non-functional libc stub.
         # We try pthread_create on general principles.

         AC_LINK_IFELSE([AC_LANG_PROGRAM([#include <pthread.h>
 #                       if $ax_pthread_check_cond
 #                        error "$ax_pthread_check_macro must be defined"
 #                       endif
                         static void *some_global = NULL;
                         static void routine(void *a)
                           {
                              /* To avoid any unused-parameter or
                                 unused-but-set-parameter warning.  */
                              some_global = a;
                           }
                         static void *start_routine(void *a) { return a; }],
                        [pthread_t th; pthread_attr_t attr;
                         pthread_create(&th, 0, start_routine, 0);
                         pthread_join(th, 0);
                         pthread_attr_init(&attr);
                         pthread_cleanup_push(routine, 0);
                         pthread_cleanup_pop(0) /* ; */])],
             [ax_pthread_ok=yes],
             [])

         CFLAGS="$ax_pthread_save_CFLAGS"
         LIBS="$ax_pthread_save_LIBS"

         AC_MSG_RESULT([$ax_pthread_ok])
         AS_IF([test "x$ax_pthread_ok" = "xyes"], [break])

         PTHREAD_LIBS=""
         PTHREAD_CFLAGS=""
 done
 fi


 # Clang needs special handling, because older versions handle the -pthread
 # option in a rather... idiosyncratic way

 if test "x$ax_pthread_clang" = "xyes"; then

         # Clang takes -pthread; it has never supported any other flag

         # (Note 1: This will need to be revisited if a system that Clang
         # supports has POSIX threads in a separate library.  This tends not
         # to be the way of modern systems, but it's conceivable.)

         # (Note 2: On some systems, notably Darwin, -pthread is not needed
         # to get POSIX threads support; the API is always present and
         # active.  We could reasonably leave PTHREAD_CFLAGS empty.  But
         # -pthread does define _REENTRANT, and while the Darwin headers
         # ignore this macro, third-party headers might not.)

         # However, older versions of Clang make a point of warning the user
         # that, in an invocation where only linking and no compilation is
         # taking place, the -pthread option has no effect ("argument unused
         # during compilation").  They expect -pthread to be passed in only
         # when source code is being compiled.
         #
         # Problem is, this is at odds with the way Automake and most other
         # C build frameworks function, which is that the same flags used in
         # compilation (CFLAGS) are also used in linking.  Many systems
         # supported by AX_PTHREAD require exactly this for POSIX threads
         # support, and in fact it is often not straightforward to specify a
         # flag that is used only in the compilation phase and not in
         # linking.  Such a scenario is extremely rare in practice.
         #
         # Even though use of the -pthread flag in linking would only print
         # a warning, this can be a nuisance for well-run software projects
         # that build with -Werror.  So if the active version of Clang has
         # this misfeature, we search for an option to squash it.

         AC_CACHE_CHECK([whether Clang needs flag to prevent "argument unused" warning when linking with -pthread],
             [ax_cv_PTHREAD_CLANG_NO_WARN_FLAG],
             [ax_cv_PTHREAD_CLANG_NO_WARN_FLAG=unknown
              # Create an alternate version of $ac_link that compiles and
              # links in two steps (.c -> .o, .o -> exe) instead of one
              # (.c -> exe), because the warning occurs only in the second
              # step
              ax_pthread_save_ac_link="$ac_link"
              ax_pthread_sed='s/conftest\.\$ac_ext/conftest.$ac_objext/g'
              ax_pthread_link_step=`$as_echo "$ac_link" | sed "$ax_pthread_sed"`
              ax_pthread_2step_ac_link="($ac_compile) && (echo ==== >&5) && ($ax_pthread_link_step)"
              ax_pthread_save_CFLAGS="$CFLAGS"
              for ax_pthread_try in '' -Qunused-arguments -Wno-unused-command-line-argument unknown; do
                 AS_IF([test "x$ax_pthread_try" = "xunknown"], [break])
                 CFLAGS="-Werror -Wunknown-warning-option $ax_pthread_try -pthread $ax_pthread_save_CFLAGS"
                 ac_link="$ax_pthread_save_ac_link"
                 AC_LINK_IFELSE([AC_LANG_SOURCE([[int main(void){return 0;}]])],
                     [ac_link="$ax_pthread_2step_ac_link"
                      AC_LINK_IFELSE([AC_LANG_SOURCE([[int main(void){return 0;}]])],
                          [break])
                     ])
              done
              ac_link="$ax_pthread_save_ac_link"
              CFLAGS="$ax_pthread_save_CFLAGS"
              AS_IF([test "x$ax_pthread_try" = "x"], [ax_pthread_try=no])
              ax_cv_PTHREAD_CLANG_NO_WARN_FLAG="$ax_pthread_try"
             ])

         case "$ax_cv_PTHREAD_CLANG_NO_WARN_FLAG" in
                 no | unknown) ;;
                 *) PTHREAD_CFLAGS="$ax_cv_PTHREAD_CLANG_NO_WARN_FLAG $PTHREAD_CFLAGS" ;;
         esac

 fi # $ax_pthread_clang = yes


 # Various other checks:
 if test "x$ax_pthread_ok" = "xyes"; then
         ax_pthread_save_CFLAGS="$CFLAGS"
         ax_pthread_save_LIBS="$LIBS"
         CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
         LIBS="$PTHREAD_LIBS $LIBS"

         # Detect AIX lossage: JOINABLE attribute is called UNDETACHED.
         AC_CACHE_CHECK([for joinable pthread attribute],
             [ax_cv_PTHREAD_JOINABLE_ATTR],
             [ax_cv_PTHREAD_JOINABLE_ATTR=unknown
              for ax_pthread_attr in PTHREAD_CREATE_JOINABLE PTHREAD_CREATE_UNDETACHED; do
                  AC_LINK_IFELSE([AC_LANG_PROGRAM([#include <pthread.h>],
                                                  [int attr = $ax_pthread_attr; return attr /* ; */])],
                                 [ax_cv_PTHREAD_JOINABLE_ATTR=$ax_pthread_attr; break],
                                 [])
              done
             ])
         AS_IF([test "x$ax_cv_PTHREAD_JOINABLE_ATTR" != "xunknown" && \
                test "x$ax_cv_PTHREAD_JOINABLE_ATTR" != "xPTHREAD_CREATE_JOINABLE" && \
                test "x$ax_pthread_joinable_attr_defined" != "xyes"],
               [AC_DEFINE_UNQUOTED([PTHREAD_CREATE_JOINABLE],
                                   [$ax_cv_PTHREAD_JOINABLE_ATTR],
                                   [Define to necessary symbol if this constant
                                    uses a non-standard name on your system.])
                ax_pthread_joinable_attr_defined=yes
               ])

         AC_CACHE_CHECK([whether more special flags are required for pthreads],
             [ax_cv_PTHREAD_SPECIAL_FLAGS],
             [ax_cv_PTHREAD_SPECIAL_FLAGS=no
              case $host_os in
              solaris*)
              ax_cv_PTHREAD_SPECIAL_FLAGS="-D_POSIX_PTHREAD_SEMANTICS"
              ;;
              esac
             ])
         AS_IF([test "x$ax_cv_PTHREAD_SPECIAL_FLAGS" != "xno" && \
                test "x$ax_pthread_special_flags_added" != "xyes"],
               [PTHREAD_CFLAGS="$ax_cv_PTHREAD_SPECIAL_FLAGS $PTHREAD_CFLAGS"
                ax_pthread_special_flags_added=yes])

         AC_CACHE_CHECK([for PTHREAD_PRIO_INHERIT],
             [ax_cv_PTHREAD_PRIO_INHERIT],
             [AC_LINK_IFELSE([AC_LANG_PROGRAM([[#include <pthread.h>]],
                                              [[int i = PTHREAD_PRIO_INHERIT;
                                                return i;]])],
                             [ax_cv_PTHREAD_PRIO_INHERIT=yes],
                             [ax_cv_PTHREAD_PRIO_INHERIT=no])
             ])
         AS_IF([test "x$ax_cv_PTHREAD_PRIO_INHERIT" = "xyes" && \
                test "x$ax_pthread_prio_inherit_defined" != "xyes"],
               [AC_DEFINE([HAVE_PTHREAD_PRIO_INHERIT], [1], [Have PTHREAD_PRIO_INHERIT.])
                ax_pthread_prio_inherit_defined=yes
               ])

         CFLAGS="$ax_pthread_save_CFLAGS"
         LIBS="$ax_pthread_save_LIBS"

         # More AIX lossage: compile with *_r variant
         if test "x$GCC" != "xyes"; then
             case $host_os in
                 aix*)
                 AS_CASE(["x/$CC"],
                     [x*/c89|x*/c89_128|x*/c99|x*/c99_128|x*/cc|x*/cc128|x*/xlc|x*/xlc_v6|x*/xlc128|x*/xlc128_v6],
                     [#handle absolute path differently from PATH based program lookup
                      AS_CASE(["x$CC"],
                          [x/*],
                          [AS_IF([AS_EXECUTABLE_P([${CC}_r])],[PTHREAD_CC="${CC}_r"])],
                          [AC_CHECK_PROGS([PTHREAD_CC],[${CC}_r],[$CC])])])
                 ;;
             esac
         fi
 fi

 test -n "$PTHREAD_CC" || PTHREAD_CC="$CC"

 AC_SUBST([PTHREAD_LIBS])
 AC_SUBST([PTHREAD_CFLAGS])
 AC_SUBST([PTHREAD_CC])

 # Finally, execute ACTION-IF-FOUND/ACTION-IF-NOT-FOUND:
 if test "x$ax_pthread_ok" = "xyes"; then
         ifelse([$1],,[AC_DEFINE([HAVE_PTHREAD],[1],[Define if you have POSIX threads libraries and header files.])],[$1])
         :
 else
         ax_pthread_ok=no
         $2
 fi
 AC_LANG_POP
 ])dnl AX_PTHREAD
	# ===========================================================================
	# https://www.gnu.org/software/autoconf-archive/ax_pthread.html
	# ===========================================================================
	#
	# SYNOPSIS
	#
	# AX_PTHREAD([ACTION-IF-FOUND[, ACTION-IF-NOT-FOUND]])
	#
	# DESCRIPTION
	#
	# This macro figures out how to build C programs using POSIX threads. It
	# sets the PTHREAD_LIBS output variable to the threads library and linker
	# flags, and the PTHREAD_CFLAGS output variable to any special C compiler
	# flags that are needed. (The user can also force certain compiler
	# flags/libs to be tested by setting these environment variables.)
	#
	# Also sets PTHREAD_CC to any special C compiler that is needed for
	# multi-threaded programs (defaults to the value of CC otherwise). (This
	# is necessary on AIX to use the special cc_r compiler alias.)
	#
	# NOTE: You are assumed to not only compile your program with these flags,
	# but also to link with them as well. For example, you might link with
	# $PTHREAD_CC $CFLAGS $PTHREAD_CFLAGS $LDFLAGS ... $PTHREAD_LIBS $LIBS
	#
	# If you are only building threaded programs, you may wish to use these
	# variables in your default LIBS, CFLAGS, and CC:
	#
	# LIBS="$PTHREAD_LIBS $LIBS"
	# CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
	# CC="$PTHREAD_CC"
	#
	# In addition, if the PTHREAD_CREATE_JOINABLE thread-attribute constant
	# has a nonstandard name, this macro defines PTHREAD_CREATE_JOINABLE to
	# that name (e.g. PTHREAD_CREATE_UNDETACHED on AIX).
	#
	# Also HAVE_PTHREAD_PRIO_INHERIT is defined if pthread is found and the
	# PTHREAD_PRIO_INHERIT symbol is defined when compiling with
	# PTHREAD_CFLAGS.
	#
	# ACTION-IF-FOUND is a list of shell commands to run if a threads library
	# is found, and ACTION-IF-NOT-FOUND is a list of commands to run it if it
	# is not found. If ACTION-IF-FOUND is not specified, the default action
	# will define HAVE_PTHREAD.
	#
	# Please let the authors know if this macro fails on any platform, or if
	# you have any other suggestions or comments. This macro was based on work
	# by SGJ on autoconf scripts for FFTW (http://www.fftw.org/) (with help
	# from M. Frigo), as well as ac_pthread and hb_pthread macros posted by
	# Alejandro Forero Cuervo to the autoconf macro repository. We are also
	# grateful for the helpful feedback of numerous users.
	#
	# Updated for Autoconf 2.68 by Daniel Richard G.
	#
	# LICENSE
	#
	# Copyright (c) 2008 Steven G. Johnson <stevenj@alum.mit.edu>
	# Copyright (c) 2011 Daniel Richard G. <skunk@iSKUNK.ORG>
	# Copyright (c) 2019 Marc Stevens <marc.stevens@cwi.nl>
	#
	# This program is free software: you can redistribute it and/or modify it
	# under the terms of the GNU General Public License as published by the
	# Free Software Foundation, either version 3 of the License, or (at your
	# option) any later version.
	#
	# This program is distributed in the hope that it will be useful, but
	# WITHOUT ANY WARRANTY; without even the implied warranty of
	# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
	# Public License for more details.
	#
	# You should have received a copy of the GNU General Public License along
	# with this program. If not, see <https://www.gnu.org/licenses/>.
	#
	# As a special exception, the respective Autoconf Macro's copyright owner
	# gives unlimited permission to copy, distribute and modify the configure
	# scripts that are the output of Autoconf when processing the Macro. You
	# need not follow the terms of the GNU General Public License when using
	# or distributing such scripts, even though portions of the text of the
	# Macro appear in them. The GNU General Public License (GPL) does govern
	# all other use of the material that constitutes the Autoconf Macro.
	#
	# This special exception to the GPL applies to versions of the Autoconf
	# Macro released by the Autoconf Archive. When you make and distribute a
	# modified version of the Autoconf Macro, you may extend this special
	# exception to the GPL to apply to your modified version as well.

	#serial 27

	AU_ALIAS([ACX_PTHREAD], [AX_PTHREAD])
	AC_DEFUN([AX_PTHREAD], [
	AC_REQUIRE([AC_CANONICAL_HOST])
	AC_REQUIRE([AC_PROG_CC])
	AC_REQUIRE([AC_PROG_SED])
	AC_LANG_PUSH([C])
	ax_pthread_ok=no

	# We used to check for pthread.h first, but this fails if pthread.h
	# requires special compiler flags (e.g. on Tru64 or Sequent).
	# It gets checked for in the link test anyway.

	# First of all, check if the user has set any of the PTHREAD_LIBS,
	# etcetera environment variables, and if threads linking works using
	# them:
	if test "x$PTHREAD_CFLAGS$PTHREAD_LIBS" != "x"; then
	ax_pthread_save_CC="$CC"
	ax_pthread_save_CFLAGS="$CFLAGS"
	ax_pthread_save_LIBS="$LIBS"
	AS_IF([test "x$PTHREAD_CC" != "x"], [CC="$PTHREAD_CC"])
	CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
	LIBS="$PTHREAD_LIBS $LIBS"
	AC_MSG_CHECKING([for pthread_join using $CC $PTHREAD_CFLAGS $PTHREAD_LIBS])
	AC_LINK_IFELSE([AC_LANG_CALL([], [pthread_join])], [ax_pthread_ok=yes])
	AC_MSG_RESULT([$ax_pthread_ok])
	if test "x$ax_pthread_ok" = "xno"; then
	PTHREAD_LIBS=""
	PTHREAD_CFLAGS=""
	fi
	CC="$ax_pthread_save_CC"
	CFLAGS="$ax_pthread_save_CFLAGS"
	LIBS="$ax_pthread_save_LIBS"
	fi

	# We must check for the threads library under a number of different
	# names; the ordering is very important because some systems
	# (e.g. DEC) have both -lpthread and -lpthreads, where one of the
	# libraries is broken (non-POSIX).

	# Create a list of thread flags to try. Items with a "," contain both
	# C compiler flags (before ",") and linker flags (after ","). Other items
	# starting with a "-" are C compiler flags, and remaining items are
	# library names, except for "none" which indicates that we try without
	# any flags at all, and "pthread-config" which is a program returning
	# the flags for the Pth emulation library.

	ax_pthread_flags="pthreads none -Kthread -pthread -pthreads -mthreads pthread --thread-safe -mt pthread-config"

	# The ordering is (sometimes) important. Some notes on the
	# individual items follow:

	# pthreads: AIX (must check this before -lpthread)
	# none: in case threads are in libc; should be tried before -Kthread and
	# other compiler flags to prevent continual compiler warnings
	# -Kthread: Sequent (threads in libc, but -Kthread needed for pthread.h)
	# -pthread: Linux/gcc (kernel threads), BSD/gcc (userland threads), Tru64
	# (Note: HP C rejects this with "bad form for `-t' option")
	# -pthreads: Solaris/gcc (Note: HP C also rejects)
	# -mt: Sun Workshop C (may only link SunOS threads [-lthread], but it
	# doesn't hurt to check since this sometimes defines pthreads and
	# -D_REENTRANT too), HP C (must be checked before -lpthread, which
	# is present but should not be used directly; and before -mthreads,
	# because the compiler interprets this as "-mt" + "-hreads")
	# -mthreads: Mingw32/gcc, Lynx/gcc
	# pthread: Linux, etcetera
	# --thread-safe: KAI C++
	# pthread-config: use pthread-config program (for GNU Pth library)

	case $host_os in

	freebsd*)

	# -kthread: FreeBSD kernel threads (preferred to -pthread since SMP-able)
	# lthread: LinuxThreads port on FreeBSD (also preferred to -pthread)

	ax_pthread_flags="-kthread lthread $ax_pthread_flags"
	;;

	hpux*)

	# From the cc(1) man page: "[-mt] Sets various -D flags to enable
	# multi-threading and also sets -lpthread."

	ax_pthread_flags="-mt -pthread pthread $ax_pthread_flags"
	;;

	openedition*)

	# IBM z/OS requires a feature-test macro to be defined in order to
	# enable POSIX threads at all, so give the user a hint if this is
	# not set. (We don't define these ourselves, as they can affect
	# other portions of the system API in unpredictable ways.)

	AC_EGREP_CPP([AX_PTHREAD_ZOS_MISSING],
	[
	# if !defined(_OPEN_THREADS) && !defined(_UNIX03_THREADS)
	AX_PTHREAD_ZOS_MISSING
	# endif
	],
	[AC_MSG_WARN([IBM z/OS requires -D_OPEN_THREADS or -D_UNIX03_THREADS to enable pthreads support.])])
	;;

	solaris*)

	# On Solaris (at least, for some versions), libc contains stubbed
	# (non-functional) versions of the pthreads routines, so link-based
	# tests will erroneously succeed. (N.B.: The stubs are missing
	# pthread_cleanup_push, or rather a function called by this macro,
	# so we could check for that, but who knows whether they'll stub
	# that too in a future libc.) So we'll check first for the
	# standard Solaris way of linking pthreads (-mt -lpthread).

	ax_pthread_flags="-mt,-lpthread pthread $ax_pthread_flags"
	;;
	esac

	# Are we compiling with Clang?

	AC_CACHE_CHECK([whether $CC is Clang],
	[ax_cv_PTHREAD_CLANG],
	[ax_cv_PTHREAD_CLANG=no
	# Note that Autoconf sets GCC=yes for Clang as well as GCC
	if test "x$GCC" = "xyes"; then
	AC_EGREP_CPP([AX_PTHREAD_CC_IS_CLANG],
	[/* Note: Clang 2.7 lacks __clang_[a-z]+__ */
	# if defined(__clang__) && defined(__llvm__)
	AX_PTHREAD_CC_IS_CLANG
	# endif
	],
	[ax_cv_PTHREAD_CLANG=yes])
	fi
	])
	ax_pthread_clang="$ax_cv_PTHREAD_CLANG"


	# GCC generally uses -pthread, or -pthreads on some platforms (e.g. SPARC)

	# Note that for GCC and Clang -pthread generally implies -lpthread,
	# except when -nostdlib is passed.
	# This is problematic using libtool to build C++ shared libraries with pthread:
	# [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=25460
	# [2] https://bugzilla.redhat.com/show_bug.cgi?id=661333
	# [3] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=468555
	# To solve this, first try -pthread together with -lpthread for GCC

	AS_IF([test "x$GCC" = "xyes"],
	[ax_pthread_flags="-pthread,-lpthread -pthread -pthreads $ax_pthread_flags"])

	# Clang takes -pthread (never supported any other flag), but we'll try with -lpthread first

	AS_IF([test "x$ax_pthread_clang" = "xyes"],
	[ax_pthread_flags="-pthread,-lpthread -pthread"])


	# The presence of a feature test macro requesting re-entrant function
	# definitions is, on some systems, a strong hint that pthreads support is
	# correctly enabled

	case $host_os in
	darwin* \| hpux* \| linux* \| osf* \| solaris*)
	ax_pthread_check_macro="_REENTRANT"
	;;

	aix*)
	ax_pthread_check_macro="_THREAD_SAFE"
	;;

	*)
	ax_pthread_check_macro="--"
	;;
	esac
	AS_IF([test "x$ax_pthread_check_macro" = "x--"],
	[ax_pthread_check_cond=0],
	[ax_pthread_check_cond="!defined($ax_pthread_check_macro)"])


	if test "x$ax_pthread_ok" = "xno"; then
	for ax_pthread_try_flag in $ax_pthread_flags; do

	case $ax_pthread_try_flag in
	none)
	AC_MSG_CHECKING([whether pthreads work without any flags])
	;;

	,)
	PTHREAD_CFLAGS=`echo $ax_pthread_try_flag \| sed "s/^\(.\),\(.\)$/\1/"`
	PTHREAD_LIBS=`echo $ax_pthread_try_flag \| sed "s/^\(.\),\(.\)$/\2/"`
	AC_MSG_CHECKING([whether pthreads work with "$PTHREAD_CFLAGS" and "$PTHREAD_LIBS"])
	;;

	-*)
	AC_MSG_CHECKING([whether pthreads work with $ax_pthread_try_flag])
	PTHREAD_CFLAGS="$ax_pthread_try_flag"
	;;

	pthread-config)
	AC_CHECK_PROG([ax_pthread_config], [pthread-config], [yes], [no])
	AS_IF([test "x$ax_pthread_config" = "xno"], [continue])
	PTHREAD_CFLAGS="`pthread-config --cflags`"
	PTHREAD_LIBS="`pthread-config --ldflags` `pthread-config --libs`"
	;;

	*)
	AC_MSG_CHECKING([for the pthreads library -l$ax_pthread_try_flag])
	PTHREAD_LIBS="-l$ax_pthread_try_flag"
	;;
	esac

	ax_pthread_save_CFLAGS="$CFLAGS"
	ax_pthread_save_LIBS="$LIBS"
	CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
	LIBS="$PTHREAD_LIBS $LIBS"

	# Check for various functions. We must include pthread.h,
	# since some functions may be macros. (On the Sequent, we
	# need a special flag -Kthread to make this header compile.)
	# We check for pthread_join because it is in -lpthread on IRIX
	# while pthread_create is in libc. We check for pthread_attr_init
	# due to DEC craziness with -lpthreads. We check for
	# pthread_cleanup_push because it is one of the few pthread
	# functions on Solaris that doesn't have a non-functional libc stub.
	# We try pthread_create on general principles.

	AC_LINK_IFELSE([AC_LANG_PROGRAM([#include <pthread.h>
	# if $ax_pthread_check_cond
	# error "$ax_pthread_check_macro must be defined"
	# endif
	static void *some_global = NULL;
	static void routine(void *a)
	{
	/* To avoid any unused-parameter or
	unused-but-set-parameter warning. */
	some_global = a;
	}
	static void start_routine(void a) { return a; }],
	[pthread_t th; pthread_attr_t attr;
	pthread_create(&th, 0, start_routine, 0);
	pthread_join(th, 0);
	pthread_attr_init(&attr);
	pthread_cleanup_push(routine, 0);
	pthread_cleanup_pop(0) /* ; */])],
	[ax_pthread_ok=yes],
	[])

	CFLAGS="$ax_pthread_save_CFLAGS"
	LIBS="$ax_pthread_save_LIBS"

	AC_MSG_RESULT([$ax_pthread_ok])
	AS_IF([test "x$ax_pthread_ok" = "xyes"], [break])

	PTHREAD_LIBS=""
	PTHREAD_CFLAGS=""
	done
	fi


	# Clang needs special handling, because older versions handle the -pthread
	# option in a rather... idiosyncratic way

	if test "x$ax_pthread_clang" = "xyes"; then

	# Clang takes -pthread; it has never supported any other flag

	# (Note 1: This will need to be revisited if a system that Clang
	# supports has POSIX threads in a separate library. This tends not
	# to be the way of modern systems, but it's conceivable.)

	# (Note 2: On some systems, notably Darwin, -pthread is not needed
	# to get POSIX threads support; the API is always present and
	# active. We could reasonably leave PTHREAD_CFLAGS empty. But
	# -pthread does define _REENTRANT, and while the Darwin headers
	# ignore this macro, third-party headers might not.)

	# However, older versions of Clang make a point of warning the user
	# that, in an invocation where only linking and no compilation is
	# taking place, the -pthread option has no effect ("argument unused
	# during compilation"). They expect -pthread to be passed in only
	# when source code is being compiled.
	#
	# Problem is, this is at odds with the way Automake and most other
	# C build frameworks function, which is that the same flags used in
	# compilation (CFLAGS) are also used in linking. Many systems
	# supported by AX_PTHREAD require exactly this for POSIX threads
	# support, and in fact it is often not straightforward to specify a
	# flag that is used only in the compilation phase and not in
	# linking. Such a scenario is extremely rare in practice.
	#
	# Even though use of the -pthread flag in linking would only print
	# a warning, this can be a nuisance for well-run software projects
	# that build with -Werror. So if the active version of Clang has
	# this misfeature, we search for an option to squash it.

	AC_CACHE_CHECK([whether Clang needs flag to prevent "argument unused" warning when linking with -pthread],
	[ax_cv_PTHREAD_CLANG_NO_WARN_FLAG],
	[ax_cv_PTHREAD_CLANG_NO_WARN_FLAG=unknown
	# Create an alternate version of $ac_link that compiles and
	# links in two steps (.c -> .o, .o -> exe) instead of one
	# (.c -> exe), because the warning occurs only in the second
	# step
	ax_pthread_save_ac_link="$ac_link"
	ax_pthread_sed='s/conftest\.\$ac_ext/conftest.$ac_objext/g'
	ax_pthread_link_step=`$as_echo "$ac_link" \| sed "$ax_pthread_sed"`
	ax_pthread_2step_ac_link="($ac_compile) && (echo ==== >&5) && ($ax_pthread_link_step)"
	ax_pthread_save_CFLAGS="$CFLAGS"
	for ax_pthread_try in '' -Qunused-arguments -Wno-unused-command-line-argument unknown; do
	AS_IF([test "x$ax_pthread_try" = "xunknown"], [break])
	CFLAGS="-Werror -Wunknown-warning-option $ax_pthread_try -pthread $ax_pthread_save_CFLAGS"
	ac_link="$ax_pthread_save_ac_link"
	AC_LINK_IFELSE([AC_LANG_SOURCE([[int main(void){return 0;}]])],
	[ac_link="$ax_pthread_2step_ac_link"
	AC_LINK_IFELSE([AC_LANG_SOURCE([[int main(void){return 0;}]])],
	[break])
	])
	done
	ac_link="$ax_pthread_save_ac_link"
	CFLAGS="$ax_pthread_save_CFLAGS"
	AS_IF([test "x$ax_pthread_try" = "x"], [ax_pthread_try=no])
	ax_cv_PTHREAD_CLANG_NO_WARN_FLAG="$ax_pthread_try"
	])

	case "$ax_cv_PTHREAD_CLANG_NO_WARN_FLAG" in
	no \| unknown) ;;
	*) PTHREAD_CFLAGS="$ax_cv_PTHREAD_CLANG_NO_WARN_FLAG $PTHREAD_CFLAGS" ;;
	esac

	fi # $ax_pthread_clang = yes



	# Various other checks:
	if test "x$ax_pthread_ok" = "xyes"; then
	ax_pthread_save_CFLAGS="$CFLAGS"
	ax_pthread_save_LIBS="$LIBS"
	CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
	LIBS="$PTHREAD_LIBS $LIBS"

	# Detect AIX lossage: JOINABLE attribute is called UNDETACHED.
	AC_CACHE_CHECK([for joinable pthread attribute],
	[ax_cv_PTHREAD_JOINABLE_ATTR],
	[ax_cv_PTHREAD_JOINABLE_ATTR=unknown
	for ax_pthread_attr in PTHREAD_CREATE_JOINABLE PTHREAD_CREATE_UNDETACHED; do
	AC_LINK_IFELSE([AC_LANG_PROGRAM([#include <pthread.h>],
	[int attr = $ax_pthread_attr; return attr /* ; */])],
	[ax_cv_PTHREAD_JOINABLE_ATTR=$ax_pthread_attr; break],
	[])
	done
	])
	AS_IF([test "x$ax_cv_PTHREAD_JOINABLE_ATTR" != "xunknown" && \
	test "x$ax_cv_PTHREAD_JOINABLE_ATTR" != "xPTHREAD_CREATE_JOINABLE" && \
	test "x$ax_pthread_joinable_attr_defined" != "xyes"],
	[AC_DEFINE_UNQUOTED([PTHREAD_CREATE_JOINABLE],
	[$ax_cv_PTHREAD_JOINABLE_ATTR],
	[Define to necessary symbol if this constant
	uses a non-standard name on your system.])
	ax_pthread_joinable_attr_defined=yes
	])

	AC_CACHE_CHECK([whether more special flags are required for pthreads],
	[ax_cv_PTHREAD_SPECIAL_FLAGS],
	[ax_cv_PTHREAD_SPECIAL_FLAGS=no
	case $host_os in
	solaris*)
	ax_cv_PTHREAD_SPECIAL_FLAGS="-D_POSIX_PTHREAD_SEMANTICS"
	;;
	esac
	])
	AS_IF([test "x$ax_cv_PTHREAD_SPECIAL_FLAGS" != "xno" && \
	test "x$ax_pthread_special_flags_added" != "xyes"],
	[PTHREAD_CFLAGS="$ax_cv_PTHREAD_SPECIAL_FLAGS $PTHREAD_CFLAGS"
	ax_pthread_special_flags_added=yes])

	AC_CACHE_CHECK([for PTHREAD_PRIO_INHERIT],
	[ax_cv_PTHREAD_PRIO_INHERIT],
	[AC_LINK_IFELSE([AC_LANG_PROGRAM([[#include <pthread.h>]],
	[[int i = PTHREAD_PRIO_INHERIT;
	return i;]])],
	[ax_cv_PTHREAD_PRIO_INHERIT=yes],
	[ax_cv_PTHREAD_PRIO_INHERIT=no])
	])
	AS_IF([test "x$ax_cv_PTHREAD_PRIO_INHERIT" = "xyes" && \
	test "x$ax_pthread_prio_inherit_defined" != "xyes"],
	[AC_DEFINE([HAVE_PTHREAD_PRIO_INHERIT], [1], [Have PTHREAD_PRIO_INHERIT.])
	ax_pthread_prio_inherit_defined=yes
	])

	CFLAGS="$ax_pthread_save_CFLAGS"
	LIBS="$ax_pthread_save_LIBS"

	# More AIX lossage: compile with *_r variant
	if test "x$GCC" != "xyes"; then
	case $host_os in
	aix*)
	AS_CASE(["x/$CC"],
	[x/c89\|x/c89_128\|x/c99\|x/c99_128\|x/cc\|x/cc128\|x/xlc\|x/xlc_v6\|x/xlc128\|x/xlc128_v6],
	[#handle absolute path differently from PATH based program lookup
	AS_CASE(["x$CC"],
	[x/*],
	[AS_IF([AS_EXECUTABLE_P([${CC}_r])],[PTHREAD_CC="${CC}_r"])],
	[AC_CHECK_PROGS([PTHREAD_CC],[${CC}_r],[$CC])])])
	;;
	esac
	fi
	fi

	test -n "$PTHREAD_CC" \|\| PTHREAD_CC="$CC"

	AC_SUBST([PTHREAD_LIBS])
	AC_SUBST([PTHREAD_CFLAGS])
	AC_SUBST([PTHREAD_CC])

	# Finally, execute ACTION-IF-FOUND/ACTION-IF-NOT-FOUND:
	if test "x$ax_pthread_ok" = "xyes"; then
	ifelse([$1],,[AC_DEFINE([HAVE_PTHREAD],[1],[Define if you have POSIX threads libraries and header files.])],[$1])
	:
	else
	ax_pthread_ok=no
	$2
	fi
	AC_LANG_POP
	])dnl AX_PTHREAD