Fix autoconf's check for create_timer()

GHC build system have custom autoconf check for `create_timer()`
function from librt. Check description says that it checks for
`CLOCK_REALTIME` timer, but checking code also checks for
`CLOCK_PROCESS_CPUTIME_ID` timer, which is not commonly present (for
example, FreeBSD doesn't have it). This makes whole check fail despite
the fact that FreeBSD have `create_timer()` call and supports
`CLOCK_REALTIME`. As a consequence, GHC RTS falls back to using SIGALRM
for its timing machinery. Not only it's very ancient codepath, it also
break some FFI bindings to C code that isn't prepared for syscall
interruption caused by SIGALRM delivery.

Grepping through ghc source code reveals that `USE_TIMER_CREATE`
defininition in the config.h doesn't imply having
`CLOCK_PROCESS_CPUTIME_ID`. The only place where
`CLOCK_PROCESS_CPUTIME_ID` is used is rts/posix/GetTime.c and this code
handles the absence of `CLOCK_PROCESS_CPUTIME_ID` gracefully.

This patch makes autoconf checking code to check only for
`timer_create(CLOCK_REALTIME, ...)` and fixes check description.

Reviewed By: austin

Differential Revision: https://phabricator.haskell.org/D831

1 files changed, 2 insertions, 32 deletions

diff --git a/aclocal.m4 b/aclocal.m4
index 226e15aec5..33a51badbb 100644
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -1654,7 +1654,7 @@ then
   then
     # We can't test timer_create when we're cross-compiling, so we
     # optimistiaclly assume that it actually works properly.
-    AC_DEFINE([USE_TIMER_CREATE], 1,  [Define to 1 if we can use timer_create(CLOCK_PROCESS_CPUTIME_ID,...)])
+    AC_DEFINE([USE_TIMER_CREATE], 1,  [Define to 1 if we can use timer_create(CLOCK_REALTIME,...)])
   else
   AC_CACHE_CHECK([for a working timer_create(CLOCK_REALTIME)],
     [fptools_cv_timer_create_works],
@@ -1715,36 +1715,6 @@ int main(int argc, char *argv[])
     }
     alarm(1);
 
-    if (timer_create(CLOCK_PROCESS_CPUTIME_ID, &ev, &timer) != 0) {
-        fprintf(stderr,"No CLOCK_PROCESS_CPUTIME_ID timer\n");
-       exit(1);
-    }
-
-    it.it_value.tv_sec = 0;
-    it.it_value.tv_nsec = 1;
-    it.it_interval = it.it_value;
-    if (timer_settime(timer, 0, &it, NULL) != 0) {
-        fprintf(stderr,"settime problem\n");
-        exit(4);
-    }
-
-    tock = 0;
-
-    for(n = 3; n < 20000; n++){
-        for(m = 2; m <= n/2; m++){
-            if (!(n%m)) count++;
-            if (tock) goto out;
-        }
-    }
-out:
-
-    if (!tock) {
-        fprintf(stderr,"no CLOCK_PROCESS_CPUTIME_ID signal\n");
-        exit(5);
-    }
-
-    timer_delete(timer);
-
     if (timer_create(CLOCK_REALTIME, &ev, &timer) != 0) {
         fprintf(stderr,"No CLOCK_REALTIME timer\n");
         exit(2);
@@ -1777,7 +1747,7 @@ out:
   ])
 case $fptools_cv_timer_create_works in
     yes) AC_DEFINE([USE_TIMER_CREATE], 1,
-                   [Define to 1 if we can use timer_create(CLOCK_PROCESS_CPUTIME_ID,...)]);;
+                   [Define to 1 if we can use timer_create(CLOCK_REALTIME,...)]);;
 esac
   fi
 fi