From: Michael Jeanson Date: Thu, 23 Jun 2016 19:20:31 +0000 (-0400) Subject: Fix: update ax_pthread macro to handle newer clang X-Git-Tag: v0.10.0~29 X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=7be759d1adf95b168f09e513232ea26de15e1eaf;p=userspace-rcu.git Fix: update ax_pthread macro to handle newer clang Signed-off-by: Michael Jeanson Signed-off-by: Mathieu Desnoyers --- diff --git a/m4/ax_pthread.m4 b/m4/ax_pthread.m4 index d383ad5..4c4051e 100644 --- a/m4/ax_pthread.m4 +++ b/m4/ax_pthread.m4 @@ -19,10 +19,10 @@ # 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 link it with them as well. e.g. you should link with +# but also to link with them as well. For example, you might link with # $PTHREAD_CC $CFLAGS $PTHREAD_CFLAGS $LDFLAGS ... $PTHREAD_LIBS $LIBS # -# If you are only building threads programs, you may wish to use these +# If you are only building threaded programs, you may wish to use these # variables in your default LIBS, CFLAGS, and CC: # # LIBS="$PTHREAD_LIBS $LIBS" @@ -30,8 +30,8 @@ # CC="$PTHREAD_CC" # # In addition, if the PTHREAD_CREATE_JOINABLE thread-attribute constant -# has a nonstandard name, defines PTHREAD_CREATE_JOINABLE to that name -# (e.g. PTHREAD_CREATE_UNDETACHED on AIX). +# 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 @@ -82,35 +82,40 @@ # modified version of the Autoconf Macro, you may extend this special # exception to the GPL to apply to your modified version as well. -#serial 21 +#serial 23 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 True64 or Sequent). +# 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"$PTHREAD_LIBS$PTHREAD_CFLAGS" != x; then - save_CFLAGS="$CFLAGS" +if test "x$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 $PTHREAD_CFLAGS" - save_LIBS="$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], [ax_pthread_ok=yes]) + 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"$ax_pthread_ok" = xno; then + if test "x$ax_pthread_ok" = "xno"; then PTHREAD_LIBS="" PTHREAD_CFLAGS="" fi - LIBS="$save_LIBS" - CFLAGS="$save_CFLAGS" + 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 @@ -123,7 +128,7 @@ fi # 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 -kthread lthread -pthread -pthreads -mthreads pthread --thread-safe -mt pthread-config" +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: @@ -132,82 +137,225 @@ ax_pthread_flags="pthreads none -Kthread -kthread lthread -pthread -pthreads -mt # 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 +# -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 too; -# also defines -D_REENTRANT) -# ... -mt is also the pthreads flag for HP/aCC +# 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 +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. (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: + # 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) - ax_pthread_flags="-pthreads pthread -mt -pthread $ax_pthread_flags" +AS_IF([test "x$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" ;; - darwin*) - ax_pthread_flags="-pthread $ax_pthread_flags" + aix*) + ax_pthread_check_macro="_THREAD_SAFE" + ;; + + *) + ax_pthread_check_macro="--" ;; esac +AS_IF([test "x$ax_pthread_check_macro" = "x--"], + [ax_pthread_check_cond=0], + [ax_pthread_check_cond="!defined($ax_pthread_check_macro)"]) + +# 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="$ax_pthread_try" + ]) -# Clang doesn't consider unrecognized options an error unless we specify -# -Werror. We throw in some extra Clang-specific options to ensure that -# this doesn't happen for GCC, which also accepts -Werror. + case "$ax_cv_PTHREAD_CLANG_NO_WARN_FLAG" in + no | unknown) ;; + *) PTHREAD_CFLAGS="$ax_cv_PTHREAD_CLANG_NO_WARN_FLAG $PTHREAD_CFLAGS" ;; + esac -AC_MSG_CHECKING([if compiler needs -Werror to reject unknown flags]) -save_CFLAGS="$CFLAGS" -ax_pthread_extra_flags="-Werror" -CFLAGS="$CFLAGS $ax_pthread_extra_flags -Wunknown-warning-option -Wsizeof-array-argument" -AC_COMPILE_IFELSE([AC_LANG_PROGRAM([int foo(void);],[foo()])], - [AC_MSG_RESULT([yes])], - [ax_pthread_extra_flags= - AC_MSG_RESULT([no])]) -CFLAGS="$save_CFLAGS" +fi # $ax_pthread_clang = yes -if test x"$ax_pthread_ok" = xno; then -for flag in $ax_pthread_flags; do +if test "x$ax_pthread_ok" = "xno"; then +for ax_pthread_try_flag in $ax_pthread_flags; do - case $flag in + 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 $flag]) - PTHREAD_CFLAGS="$flag" + 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]) - if test x"$ax_pthread_config" = xno; then continue; fi + AS_IF([test "x$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$flag]) - PTHREAD_LIBS="-l$flag" + AC_MSG_CHECKING([for the pthreads library -l$ax_pthread_try_flag]) + PTHREAD_LIBS="-l$ax_pthread_try_flag" ;; esac - save_LIBS="$LIBS" - save_CFLAGS="$CFLAGS" + ax_pthread_save_CFLAGS="$CFLAGS" + ax_pthread_save_LIBS="$LIBS" + CFLAGS="$CFLAGS $PTHREAD_CFLAGS" LIBS="$PTHREAD_LIBS $LIBS" - CFLAGS="$CFLAGS $PTHREAD_CFLAGS $ax_pthread_extra_flags" # Check for various functions. We must include pthread.h, # since some functions may be macros. (On the Sequent, we @@ -218,7 +366,11 @@ for flag in $ax_pthread_flags; do # 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 +# 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; @@ -227,16 +379,14 @@ for flag in $ax_pthread_flags; do pthread_attr_init(&attr); pthread_cleanup_push(routine, 0); pthread_cleanup_pop(0) /* ; */])], - [ax_pthread_ok=yes], - []) + [ax_pthread_ok=yes], + []) - LIBS="$save_LIBS" - CFLAGS="$save_CFLAGS" + CFLAGS="$ax_pthread_save_CFLAGS" + LIBS="$ax_pthread_save_LIBS" AC_MSG_RESULT([$ax_pthread_ok]) - if test "x$ax_pthread_ok" = xyes; then - break; - fi + AS_IF([test "x$ax_pthread_ok" = "xyes"], [break]) PTHREAD_LIBS="" PTHREAD_CFLAGS="" @@ -244,71 +394,74 @@ done fi # Various other checks: -if test "x$ax_pthread_ok" = xyes; then - save_LIBS="$LIBS" - LIBS="$PTHREAD_LIBS $LIBS" - save_CFLAGS="$CFLAGS" +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_MSG_CHECKING([for joinable pthread attribute]) - attr_name=unknown - for attr in PTHREAD_CREATE_JOINABLE PTHREAD_CREATE_UNDETACHED; do - AC_LINK_IFELSE([AC_LANG_PROGRAM([#include ], - [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 ${host_os} in - aix* | freebsd* | darwin*) flag="-D_THREAD_SAFE";; - osf* | hpux*) flag="-D_REENTRANT";; - solaris*) - if test "$GCC" = "yes"; then - flag="-D_REENTRANT" - else - # TODO: What about Clang on Solaris? - flag="-mt -D_REENTRANT" - fi - ;; - esac - AC_MSG_RESULT([$flag]) - if test "x$flag" != xno; then - PTHREAD_CFLAGS="$flag $PTHREAD_CFLAGS" - fi + 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 ], + [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 $PTHREAD_CFLAGS" + ax_pthread_special_flags_added=yes]) AC_CACHE_CHECK([for PTHREAD_PRIO_INHERIT], - [ax_cv_PTHREAD_PRIO_INHERIT], [ - AC_LINK_IFELSE([AC_LANG_PROGRAM([[#include ]], - [[int i = PTHREAD_PRIO_INHERIT;]])], - [ax_cv_PTHREAD_PRIO_INHERIT=yes], - [ax_cv_PTHREAD_PRIO_INHERIT=no]) + [ax_cv_PTHREAD_PRIO_INHERIT], + [AC_LINK_IFELSE([AC_LANG_PROGRAM([[#include ]], + [[int i = PTHREAD_PRIO_INHERIT;]])], + [ax_cv_PTHREAD_PRIO_INHERIT=yes], + [ax_cv_PTHREAD_PRIO_INHERIT=no]) ]) - AS_IF([test "x$ax_cv_PTHREAD_PRIO_INHERIT" = "xyes"], - [AC_DEFINE([HAVE_PTHREAD_PRIO_INHERIT], [1], [Have PTHREAD_PRIO_INHERIT.])]) + 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 + ]) - LIBS="$save_LIBS" - CFLAGS="$save_CFLAGS" + CFLAGS="$ax_pthread_save_CFLAGS" + LIBS="$ax_pthread_save_LIBS" # More AIX lossage: compile with *_r variant - if test "x$GCC" != xyes; then + if test "x$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],[$CC])])]) + [x*/c89|x*/c89_128|x*/c99|x*/c99_128|x*/cc|x*/cc128|x*/xlc|x*/xlc_v6|x*/xlc128|x*/xlc128_v6], + [#handle absolute path differently from PATH based program lookup + AS_CASE(["x$CC"], + [x/*], + [AS_IF([AS_EXECUTABLE_P([${CC}_r])],[PTHREAD_CC="${CC}_r"])], + [AC_CHECK_PROGS([PTHREAD_CC],[${CC}_r],[$CC])])]) ;; esac fi @@ -321,7 +474,7 @@ AC_SUBST([PTHREAD_CFLAGS]) AC_SUBST([PTHREAD_CC]) # Finally, execute ACTION-IF-FOUND/ACTION-IF-NOT-FOUND: -if test x"$ax_pthread_ok" = xyes; then +if test "x$ax_pthread_ok" = "xyes"; then ifelse([$1],,[AC_DEFINE([HAVE_PTHREAD],[1],[Define if you have POSIX threads libraries and header files.])],[$1]) : else