configure: always check for pthreads when --enable-pthreads is specified

[Keruspe]

Otherwise if threaded resolver is disabled, configure will fail with
configure: error: --enable-pthreads but pthreads was not found

[mention-bot]

@Keruspe, thanks for your PR! By analyzing the history of the files in this pull request, we identified @bagder, @yangtse and @dfandrich to be potential reviewers.

[jay]

Can you give me the exact options to reproduce this in configure? When --enable-pthreads was added I built with and without the threaded resolver and didn't have this problem. Note pthreads detection is supposed to be ignored if --disable-rt is used. Perhaps we should add an error in case of explicit --disable-rt --enable-phtreads:

diff --git a/configure.ac b/configure.ac
index 1e76c49..55d057f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -3420,6 +3420,9 @@ AC_HELP_STRING([--disable-pthreads],[Disable POSIX threads]),
        want_pthreads=no
        ;;
   *)   AC_MSG_RESULT(yes)
+       if test "$dontwant_rt" = "yes"; then
+         AC_MSG_ERROR([options --disable-rt and --enable-pthreads are mutually exclusive])
+       fi
        want_pthreads=yes
        ;;
   esac ], [

[Keruspe]

Just ./configure --enable-pthreads without any other argument.

The problem is that pthreads checks are only performed if --enable-rt, and afterwards, if --enable-pthreads was specified and pthreads not found, we hit an error. As the script never actually checked for pthreads, we hit that error, which is really misleading.

The two solution here I guess are either to error out as you suggested or make --enable-pthreads a noop when --disable-rt (which is what my patch does)

[jay]

Thanks, I see it now. Unfortunately to handle all the combinations is a little more complicated than I thought. Can you please try this:
https://github.com/curl/curl/compare/master...jay:fix_configure_enable-pthreads?expand=1

[Keruspe]

seems to work fine here with your patch

[jay]

Thanks, landed in 5f139d6.