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+# This file was copied to Cap'n Proto from the Protocol Buffers distribution,
+# version 2.3.0.
+
+# 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 <[e-mail]>
+dnl @version 2006-05-29
+dnl @license GPLWithACException
+dnl
+dnl Checks for GCC shared/pthread inconsistency based on work by
+dnl Marcin Owsiany <[e-mail]>
+
+
+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
+
+        CFLAGS="$save_CFLAGS"
+        LIBS="$save_LIBS"
+        CC="$save_CC"
+else
+        PTHREAD_CC="$CC"
+fi
+
+if test "x$acx_pthread_ok" = xyes; then
+        # One more check: If we chose to use a compiler flag like -pthread but it is combined with
+        # -nostdlib then the compiler won't implicitly link against libpthread. This can happen
+        # in particular when using some versions of libtool on some distros. See:
+        #     https://bugzilla.redhat.com/show_bug.cgi?id=661333
+
+        save_CFLAGS="$CFLAGS"
+        save_LIBS="$LIBS"
+        save_CC="$CC"
+        CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
+        LIBS="-nostdlib $PTHREAD_LIBS $LIBS -lc"
+        CC="$PTHREAD_CC"
+
+        AC_MSG_CHECKING([whether pthread flag is sufficient with -nostdlib])
+        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); ],
+                    [AC_MSG_RESULT([yes])], [
+          AC_MSG_RESULT([no])
+
+          AC_MSG_CHECKING([whether adding -lpthread fixes that])
+
+          LIBS="-nostdlib $PTHREAD_LIBS -lpthread $save_LIBS -lc"
+          AC_TRY_LINK([#include <pthread.h>],
+                      [pthread_t th; pthread_join(th, 0);
+                       pthread_attr_init(0); pthread_cleanup_push(0, 0);
+                       pthread_create(0,0,0,0); pthread_cleanup_pop(0); ],
+                      [
+            AC_MSG_RESULT([yes])
+            PTHREAD_LIBS="$PTHREAD_LIBS -lpthread"
+          ], [AC_MSG_RESULT([no])])
+        ])
+
+        CFLAGS="$save_CFLAGS"
+        LIBS="$save_LIBS"
+        CC="$save_CC"
+fi
+
+AC_SUBST(PTHREAD_LIBS)
+AC_SUBST(PTHREAD_CFLAGS)
+AC_SUBST(PTHREAD_CC)
+
+# Finally, execute ACTION-IF-FOUND/ACTION-IF-NOT-FOUND:
+if test x"$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