Make forkProcess work with +RTS -N

Consider this experimental for the time being.  There are a lot of
things that could go wrong, but I've verified that at least it works
on the test cases we have.

I also did some API cleanups while I was here.  Previously we had:

Capability * rts_eval (Capability *cap, HaskellObj p, /*out*/HaskellObj *ret);

but this API is particularly error-prone: if you forget to discard the
Capability * you passed in and use the return value instead, then
you're in for subtle bugs with +RTS -N later on.  So I changed all
these functions to this form:

void rts_eval (/* inout */ Capability **cap,
               /* in    */ HaskellObj p,
               /* out */   HaskellObj *ret)

It's much harder to use this version incorrectly, because you have to
pass the Capability in by reference.

1 files changed, 4 insertions, 5 deletions

diff --git a/rts/posix/Signals.c b/rts/posix/Signals.c
index 9f5bf9f370..38c9792552 100644
--- a/rts/posix/Signals.c
+++ b/rts/posix/Signals.c
@@ -145,11 +145,10 @@ ioManagerDie (void)
     }
 }
 
-Capability *
-ioManagerStartCap (Capability *cap)
+void
+ioManagerStartCap (Capability **cap)
 {
-    return rts_evalIO(
-        cap,&base_GHCziConcziIO_ensureIOManagerIsRunning_closure,NULL);
+    rts_evalIO(cap,&base_GHCziConcziIO_ensureIOManagerIsRunning_closure,NULL);
 }
 
 void
@@ -159,7 +158,7 @@ ioManagerStart (void)
     Capability *cap;
     if (io_manager_control_fd < 0 || io_manager_wakeup_fd < 0) {
 	cap = rts_lock();
-	cap = ioManagerStartCap(cap);
+        ioManagerStartCap(&cap);
 	rts_unlock(cap);
     }
 }