third_party/protobuf/3.6.1/m4/ax_pthread.m4 - bazel - Git at Google

 # ===========================================================================
 #        http://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>
 #
 #   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 <http://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 22

 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 starting with a "-" are
 # C compiler flags, and other 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,pthread pthread $ax_pthread_flags"
 	;;
 esac

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

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

 # 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* | freebsd*)
 	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)"])

 # 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"

 ax_pthread_clang_warning=no

 # 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.)

 	PTHREAD_CFLAGS="-pthread"
 	PTHREAD_LIBS=

 	ax_pthread_ok=yes

 	# 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

 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])
 		;;

 		-mt,pthread)
 		AC_MSG_CHECKING([whether pthreads work with -mt -lpthread])
 		PTHREAD_CFLAGS="-mt"
 		PTHREAD_LIBS="-lpthread"
 		;;

 		-*)
 		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 routine(void *a) { a = 0; }
 			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

 # 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;]])],
 			    [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
	# ===========================================================================
	# http://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>
	#
	# 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 <http://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 22

	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 starting with a "-" are
	# C compiler flags, and other 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,pthread pthread $ax_pthread_flags"
	;;
	esac

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

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

	# 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* \| freebsd*)
	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)"])

	# 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"

	ax_pthread_clang_warning=no

	# 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.)

	PTHREAD_CFLAGS="-pthread"
	PTHREAD_LIBS=

	ax_pthread_ok=yes

	# 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

	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])
	;;

	-mt,pthread)
	AC_MSG_CHECKING([whether pthreads work with -mt -lpthread])
	PTHREAD_CFLAGS="-mt"
	PTHREAD_LIBS="-lpthread"
	;;

	-*)
	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 routine(void *a) { a = 0; }
	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

	# 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;]])],
	[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