-if test "x$enable_context" = "xucontext"; then
- AC_CHECK_HEADERS([ucontext.h])
- ac_header=ucontext.h
- as_ac_Header=`echo "ac_cv_header_$ac_header" | $as_tr_sh`
- if test `eval echo '${'$as_ac_Header'}'` = yes; then
- AC_MSG_RESULT(found ucontext.h. Great!)
+AC_CHECK_HEADER(ucontext.h,,, [#include <sys/types.h>])
+AC_CHECK_FUNCS(makecontext swapcontext getcontext setcontext)
+AC_CHECK_MCSC(mcsc=yes, mcsc=no)
+
+dnl # check for pthread method
+AC_CHECK_HEADERS([pthread.h])
+AC_CHECK_LIB(pthread,pthread_create,pthread=yes, pthread=no)
+
+dnl #
+dnl # 2. make a general decision
+dnl #
+
+if test ".$mcsc" = .yes; then
+ mcsc=yes
+elif test ".$pthread" = .yes; then
+ pthread=yes
+else
+ AC_ERROR([no appropriate backend found])
+fi
+
+dnl #
+dnl # 3. allow decision to be overridden by user
+dnl #
+
+AC_MSG_CHECKING(what kind of backend should we use)
+AC_ARG_WITH(context,
+ [ --with-context=[ucontext/pthread] Use either (System V) swapcontext or pthread [[default=auto]].],,
+ with_context=auto)
+case $with_context in
+ ucontext) ;;
+ pthread) ;;
+ auto) with_context=ucontext;;
+ *) AC_MSG_ERROR("--with-context must be either ucontext or pthread") ;;
+esac
+
+if test "x$with_context" = "xucontext" ; then
+ if test ".$mcsc" = .yes; then
+ AC_MSG_RESULT(found working ucontext. Great!)
+ AC_DEFINE([USE_UCONTEXT],1,[Define if we use ucontext or not])