diff --git a/configure.ac b/configure.ac
index faa1cdc361..4e3dc61327 100644
--- a/configure.ac
+++ b/configure.ac
@@ -184,9 +184,8 @@ AS_IF([test "$with_protoc" != "no"], [
 ])
 AM_CONDITIONAL([USE_EXTERNAL_PROTOC], [test "$with_protoc" != "no"])
 
-ACX_PTHREAD
-AM_CONDITIONAL([HAVE_PTHREAD], [test "x$acx_pthread_ok" = "xyes"])
-
+AX_PTHREAD
+AM_CONDITIONAL([HAVE_PTHREAD], [test "x$ax_pthread_ok" = "xyes"])
 # We still keep this for improving pbconfig.h for unsupported platforms.
 AC_CXX_STL_HASH
 
diff --git a/m4/acx_pthread.m4 b/m4/acx_pthread.m4
deleted file mode 100644
index 89d42c7449..0000000000
--- a/m4/acx_pthread.m4
+++ /dev/null
@@ -1,397 +0,0 @@
-# This was retrieved from
-#    http://svn.0pointer.de/viewvc/trunk/common/acx_pthread.m4?revision=1277&root=avahi
-# See also (perhaps for new versions?)
-#    http://svn.0pointer.de/viewvc/trunk/common/acx_pthread.m4?root=avahi
-#
-# We've rewritten the inconsistency check code (from avahi), to work
-# more broadly.  In particular, it no longer assumes ld accepts -zdefs.
-# This caused a restructing of the code, but the functionality has only
-# changed a little.
-
-dnl @synopsis ACX_PTHREAD([ACTION-IF-FOUND[, ACTION-IF-NOT-FOUND]])
-dnl
-dnl @summary figure out how to build C programs using POSIX threads
-dnl
-dnl This macro figures out how to build C programs using POSIX threads.
-dnl It sets the PTHREAD_LIBS output variable to the threads library and
-dnl linker flags, and the PTHREAD_CFLAGS output variable to any special
-dnl C compiler flags that are needed. (The user can also force certain
-dnl compiler flags/libs to be tested by setting these environment
-dnl variables.)
-dnl
-dnl Also sets PTHREAD_CC to any special C compiler that is needed for
-dnl multi-threaded programs (defaults to the value of CC otherwise).
-dnl (This is necessary on AIX to use the special cc_r compiler alias.)
-dnl
-dnl NOTE: You are assumed to not only compile your program with these
-dnl flags, but also link it with them as well. e.g. you should link
-dnl with $PTHREAD_CC $CFLAGS $PTHREAD_CFLAGS $LDFLAGS ... $PTHREAD_LIBS
-dnl $LIBS
-dnl
-dnl If you are only building threads programs, you may wish to use
-dnl these variables in your default LIBS, CFLAGS, and CC:
-dnl
-dnl        LIBS="$PTHREAD_LIBS $LIBS"
-dnl        CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
-dnl        CC="$PTHREAD_CC"
-dnl
-dnl In addition, if the PTHREAD_CREATE_JOINABLE thread-attribute
-dnl constant has a nonstandard name, defines PTHREAD_CREATE_JOINABLE to
-dnl that name (e.g. PTHREAD_CREATE_UNDETACHED on AIX).
-dnl
-dnl ACTION-IF-FOUND is a list of shell commands to run if a threads
-dnl library is found, and ACTION-IF-NOT-FOUND is a list of commands to
-dnl run it if it is not found. If ACTION-IF-FOUND is not specified, the
-dnl default action will define HAVE_PTHREAD.
-dnl
-dnl Please let the authors know if this macro fails on any platform, or
-dnl if you have any other suggestions or comments. This macro was based
-dnl on work by SGJ on autoconf scripts for FFTW (www.fftw.org) (with
-dnl help from M. Frigo), as well as ac_pthread and hb_pthread macros
-dnl posted by Alejandro Forero Cuervo to the autoconf macro repository.
-dnl We are also grateful for the helpful feedback of numerous users.
-dnl
-dnl @category InstalledPackages
-dnl @author Steven G. Johnson <stevenj@alum.mit.edu>
-dnl @version 2006-05-29
-dnl @license GPLWithACException
-dnl 
-dnl Checks for GCC shared/pthread inconsistency based on work by
-dnl Marcin Owsiany <marcin@owsiany.pl>
-
-
-AC_DEFUN([ACX_PTHREAD], [
-AC_REQUIRE([AC_CANONICAL_HOST])
-AC_LANG_SAVE
-AC_LANG_C
-acx_pthread_ok=no
-
-# We used to check for pthread.h first, but this fails if pthread.h
-# requires special compiler flags (e.g. on True64 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"$PTHREAD_LIBS$PTHREAD_CFLAGS" != x; then
-        save_CFLAGS="$CFLAGS"
-        CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
-        save_LIBS="$LIBS"
-        LIBS="$PTHREAD_LIBS $LIBS"
-        AC_MSG_CHECKING([for pthread_join in LIBS=$PTHREAD_LIBS with CFLAGS=$PTHREAD_CFLAGS])
-        AC_TRY_LINK_FUNC(pthread_join, acx_pthread_ok=yes)
-        AC_MSG_RESULT($acx_pthread_ok)
-        if test x"$acx_pthread_ok" = xno; then
-                PTHREAD_LIBS=""
-                PTHREAD_CFLAGS=""
-        fi
-        LIBS="$save_LIBS"
-        CFLAGS="$save_CFLAGS"
-fi
-
-# We must check for the threads library under a number of different
-# names; the ordering is very important because some systems
-# (e.g. DEC) have both -lpthread and -lpthreads, where one of the
-# libraries is broken (non-POSIX).
-
-# Create a list of thread flags to try.  Items starting with a "-" are
-# C compiler flags, and other items are library names, except for "none"
-# which indicates that we try without any flags at all, and "pthread-config"
-# which is a program returning the flags for the Pth emulation library.
-
-acx_pthread_flags="pthreads none -Kthread -kthread lthread -pthread -pthreads -mthreads pthread --thread-safe -mt pthread-config"
-
-# The ordering *is* (sometimes) important.  Some notes on the
-# individual items follow:
-
-# pthreads: AIX (must check this before -lpthread)
-# none: in case threads are in libc; should be tried before -Kthread and
-#       other compiler flags to prevent continual compiler warnings
-# -Kthread: Sequent (threads in libc, but -Kthread needed for pthread.h)
-# -kthread: FreeBSD kernel threads (preferred to -pthread since SMP-able)
-# lthread: LinuxThreads port on FreeBSD (also preferred to -pthread)
-# -pthread: Linux/gcc (kernel threads), BSD/gcc (userland threads)
-# -pthreads: Solaris/gcc
-# -mthreads: Mingw32/gcc, Lynx/gcc
-# -mt: Sun Workshop C (may only link SunOS threads [-lthread], but it
-#      doesn't hurt to check since this sometimes defines pthreads too;
-#      also defines -D_REENTRANT)
-#      ... -mt is also the pthreads flag for HP/aCC
-# pthread: Linux, etcetera
-# --thread-safe: KAI C++
-# pthread-config: use pthread-config program (for GNU Pth library)
-
-case "${host_cpu}-${host_os}" in
-        *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.  (We need to link with -pthreads/-mt/
-        # -lpthread.)  (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 just look for -pthreads and -lpthread first:
-
-        acx_pthread_flags="-pthreads pthread -mt -pthread $acx_pthread_flags"
-        ;;
-esac
-
-if test x"$acx_pthread_ok" = xno; then
-for flag in $acx_pthread_flags; do
-
-        case $flag in
-                none)
-                AC_MSG_CHECKING([whether pthreads work without any flags])
-                ;;
-
-                -*)
-                AC_MSG_CHECKING([whether pthreads work with $flag])
-                PTHREAD_CFLAGS="$flag"
-                ;;
-
-		pthread-config)
-		AC_CHECK_PROG(acx_pthread_config, pthread-config, yes, no)
-		if test x"$acx_pthread_config" = xno; then continue; fi
-		PTHREAD_CFLAGS="`pthread-config --cflags`"
-		PTHREAD_LIBS="`pthread-config --ldflags` `pthread-config --libs`"
-		;;
-
-                *)
-                AC_MSG_CHECKING([for the pthreads library -l$flag])
-                PTHREAD_LIBS="-l$flag"
-                ;;
-        esac
-
-        save_LIBS="$LIBS"
-        save_CFLAGS="$CFLAGS"
-        LIBS="$PTHREAD_LIBS $LIBS"
-        CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
-
-        # Check for various functions.  We must include pthread.h,
-        # since some functions may be macros.  (On the Sequent, we
-        # need a special flag -Kthread to make this header compile.)
-        # We check for pthread_join because it is in -lpthread on IRIX
-        # while pthread_create is in libc.  We check for pthread_attr_init
-        # due to DEC craziness with -lpthreads.  We check for
-        # pthread_cleanup_push because it is one of the few pthread
-        # functions on Solaris that doesn't have a non-functional libc stub.
-        # We try pthread_create on general principles.
-        AC_TRY_LINK([#include <pthread.h>],
-                    [pthread_t th; pthread_join(th, 0);
-                     pthread_attr_init(0); pthread_cleanup_push(0, 0);
-                     pthread_create(0,0,0,0); pthread_cleanup_pop(0); ],
-                    [acx_pthread_ok=yes])
-
-        LIBS="$save_LIBS"
-        CFLAGS="$save_CFLAGS"
-
-        AC_MSG_RESULT($acx_pthread_ok)
-        if test "x$acx_pthread_ok" = xyes; then
-                break;
-        fi
-
-        PTHREAD_LIBS=""
-        PTHREAD_CFLAGS=""
-done
-fi
-
-# Various other checks:
-if test "x$acx_pthread_ok" = xyes; then
-        save_LIBS="$LIBS"
-        LIBS="$PTHREAD_LIBS $LIBS"
-        save_CFLAGS="$CFLAGS"
-        CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
-
-        # Detect AIX lossage: JOINABLE attribute is called UNDETACHED.
-	AC_MSG_CHECKING([for joinable pthread attribute])
-	attr_name=unknown
-	for attr in PTHREAD_CREATE_JOINABLE PTHREAD_CREATE_UNDETACHED; do
-	    AC_TRY_LINK([#include <pthread.h>], [int attr=$attr; return attr;],
-                        [attr_name=$attr; break])
-	done
-        AC_MSG_RESULT($attr_name)
-        if test "$attr_name" != PTHREAD_CREATE_JOINABLE; then
-            AC_DEFINE_UNQUOTED(PTHREAD_CREATE_JOINABLE, $attr_name,
-                               [Define to necessary symbol if this constant
-                                uses a non-standard name on your system.])
-        fi
-
-        AC_MSG_CHECKING([if more special flags are required for pthreads])
-        flag=no
-        case "${host_cpu}-${host_os}" in
-            *-aix* | *-freebsd* | *-darwin*) flag="-D_THREAD_SAFE";;
-            *solaris* | *-osf* | *-hpux*) flag="-D_REENTRANT";;
-        esac
-        AC_MSG_RESULT(${flag})
-        if test "x$flag" != xno; then
-            PTHREAD_CFLAGS="$flag $PTHREAD_CFLAGS"
-        fi
-
-        LIBS="$save_LIBS"
-        CFLAGS="$save_CFLAGS"
-        # More AIX lossage: must compile with xlc_r or cc_r
-	if test x"$GCC" != xyes; then
-          AC_CHECK_PROGS(PTHREAD_CC, xlc_r cc_r, ${CC})
-        else
-          PTHREAD_CC=$CC
-	fi
-
-	# The next part tries to detect GCC inconsistency with -shared on some
-	# architectures and systems. The problem is that in certain
-	# configurations, when -shared is specified, GCC "forgets" to
-	# internally use various flags which are still necessary.
-	
-	#
-	# Prepare the flags
-	#
-	save_CFLAGS="$CFLAGS"
-	save_LIBS="$LIBS"
-	save_CC="$CC"
-	
-	# Try with the flags determined by the earlier checks.
-	#
-	# -Wl,-z,defs forces link-time symbol resolution, so that the
-	# linking checks with -shared actually have any value
-	#
-	# FIXME: -fPIC is required for -shared on many architectures,
-	# so we specify it here, but the right way would probably be to
-	# properly detect whether it is actually required.
-	CFLAGS="-shared -fPIC -Wl,-z,defs $CFLAGS $PTHREAD_CFLAGS"
-	LIBS="$PTHREAD_LIBS $LIBS"
-	CC="$PTHREAD_CC"
-	
-	# In order not to create several levels of indentation, we test
-	# the value of "$done" until we find the cure or run out of ideas.
-	done="no"
-	
-	# First, make sure the CFLAGS we added are actually accepted by our
-	# compiler.  If not (and OS X's ld, for instance, does not accept -z),
-	# then we can't do this test.
-	if test x"$done" = xno; then
-	   AC_MSG_CHECKING([whether to check for GCC pthread/shared inconsistencies])
-	   AC_TRY_LINK(,, , [done=yes])
-	
-	   if test "x$done" = xyes ; then
-	      AC_MSG_RESULT([no])
-	   else
-	      AC_MSG_RESULT([yes])
-	   fi
-	fi
-	
-	if test x"$done" = xno; then
-	   AC_MSG_CHECKING([whether -pthread is sufficient with -shared])
-	   AC_TRY_LINK([#include <pthread.h>],
-	      [pthread_t th; pthread_join(th, 0);
-	      pthread_attr_init(0); pthread_cleanup_push(0, 0);
-	      pthread_create(0,0,0,0); pthread_cleanup_pop(0); ],
-	      [done=yes])
-	   
-	   if test "x$done" = xyes; then
-	      AC_MSG_RESULT([yes])
-	   else
-	      AC_MSG_RESULT([no])
-	   fi
-	fi
-	
-	#
-	# Linux gcc on some architectures such as mips/mipsel forgets
-	# about -lpthread
-	#
-	if test x"$done" = xno; then
-	   AC_MSG_CHECKING([whether -lpthread fixes that])
-	   LIBS="-lpthread $PTHREAD_LIBS $save_LIBS"
-	   AC_TRY_LINK([#include <pthread.h>],
-	      [pthread_t th; pthread_join(th, 0);
-	      pthread_attr_init(0); pthread_cleanup_push(0, 0);
-	      pthread_create(0,0,0,0); pthread_cleanup_pop(0); ],
-	      [done=yes])
-	
-	   if test "x$done" = xyes; then
-	      AC_MSG_RESULT([yes])
-	      PTHREAD_LIBS="-lpthread $PTHREAD_LIBS"
-	   else
-	      AC_MSG_RESULT([no])
-	   fi
-	fi
-	#
-	# FreeBSD 4.10 gcc forgets to use -lc_r instead of -lc
-	#
-	if test x"$done" = xno; then
-	   AC_MSG_CHECKING([whether -lc_r fixes that])
-	   LIBS="-lc_r $PTHREAD_LIBS $save_LIBS"
-	   AC_TRY_LINK([#include <pthread.h>],
-	       [pthread_t th; pthread_join(th, 0);
-	        pthread_attr_init(0); pthread_cleanup_push(0, 0);
-	        pthread_create(0,0,0,0); pthread_cleanup_pop(0); ],
-	       [done=yes])
-	
-	   if test "x$done" = xyes; then
-	      AC_MSG_RESULT([yes])
-	      PTHREAD_LIBS="-lc_r $PTHREAD_LIBS"
-	   else
-	      AC_MSG_RESULT([no])
-	   fi
-	fi
-	if test x"$done" = xno; then
-	   # OK, we have run out of ideas
-	   AC_MSG_WARN([Impossible to determine how to use pthreads with shared libraries])
-	
-	   # so it's not safe to assume that we may use pthreads
-	   acx_pthread_ok=no
-	fi
-	
-	AC_MSG_CHECKING([whether what we have so far is sufficient with -nostdlib])
-	CFLAGS="-nostdlib $CFLAGS"
-	# we need c with nostdlib
-	LIBS="$LIBS -lc"
-	AC_TRY_LINK([#include <pthread.h>],
-	      [pthread_t th; pthread_join(th, 0);
-	       pthread_attr_init(0); pthread_cleanup_push(0, 0);
-	       pthread_create(0,0,0,0); pthread_cleanup_pop(0); ],
-	      [done=yes],[done=no])
-
-	if test "x$done" = xyes; then
-	   AC_MSG_RESULT([yes])
-	else
-	   AC_MSG_RESULT([no])
-	fi
-	
-	if test x"$done" = xno; then
-	   AC_MSG_CHECKING([whether -lpthread saves the day])
-	   LIBS="-lpthread $LIBS"
-	   AC_TRY_LINK([#include <pthread.h>],
-	      [pthread_t th; pthread_join(th, 0);
-	       pthread_attr_init(0); pthread_cleanup_push(0, 0);
-	       pthread_create(0,0,0,0); pthread_cleanup_pop(0); ],
-	      [done=yes],[done=no])
-
-	   if test "x$done" = xyes; then
-	      AC_MSG_RESULT([yes])
-	      PTHREAD_LIBS="$PTHREAD_LIBS -lpthread"
-	   else
-	      AC_MSG_RESULT([no])
-	      AC_MSG_WARN([Impossible to determine how to use pthreads with shared libraries and -nostdlib])
-	   fi
-	fi
-
-	CFLAGS="$save_CFLAGS"
-	LIBS="$save_LIBS"
-	CC="$save_CC"
-else
-        PTHREAD_CC="$CC"
-fi
-
-AC_SUBST(PTHREAD_LIBS)
-AC_SUBST(PTHREAD_CFLAGS)
-AC_SUBST(PTHREAD_CC)
-
-# Finally, execute ACTION-IF-FOUND/ACTION-IF-NOT-FOUND:
-if test x"$acx_pthread_ok" = xyes; then
-        ifelse([$1],,AC_DEFINE(HAVE_PTHREAD,1,[Define if you have POSIX threads libraries and header files.]),[$1])
-        :
-else
-        acx_pthread_ok=no
-        $2
-fi
-AC_LANG_RESTORE
-])dnl ACX_PTHREAD
diff --git a/m4/ax_pthread.m4 b/m4/ax_pthread.m4
new file mode 100644
index 0000000000..d218d1af73
--- /dev/null
+++ b/m4/ax_pthread.m4
@@ -0,0 +1,485 @@
+# ===========================================================================
+#        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