[PATCH 2/5] os: add OsBlockSIGIO and OsReleaseSIGIO

[Peter Hutterer]

On Mon, Jul 02, 2012 at 11:30:13PM -0700, Keith Packard wrote:
> Peter Hutterer <peter.hutterer at who-t.net> writes:
> 
> >  void
> >  OsReleaseSignals(void)
> >  {
> >  #ifdef SIG_BLOCK
> >      if (--BlockedSignalCount == 0) {
> >          sigprocmask(SIG_SETMASK, &PreviousSignalMask, 0);
> > +        OsReleaseSIGIO();
> >      }
> >  #endif
> 
> Should you use SIG_UNBLOCK instead of SIG_SETMASK? It took me several
> minutes to figure out that SIG_SETMASK will work because
> PreviousSignalMask *always* contains SIGIO as it is set after
> the call to OsBlockSIGIO in OsBlockSignals. Either that, or a comment
> explaining why this works so future-me doesn't get confused again...
 
We'd have to mask out SIGIO from PrevSignalMask then for SIG_UNBLOCK to
work:

diff --git a/os/utils.c b/os/utils.c
index 55f58b9..0f6419c 100644
--- a/os/utils.c
+++ b/os/utils.c
@@ -1179,6 +1179,11 @@ OsBlockSignals(void)
         sigaddset(&set, SIGTTOU);
         sigaddset(&set, SIGCHLD);
         sigprocmask(SIG_BLOCK, &set, &PreviousSignalMask);
+
+#ifdef SIGIO
+        /* OsBlockSIGIO is in charge of SIGIO*/
+        sigdelset(&PreviousSignalMask, SIGIO);
+#endif
     }
 #endif
 }
@@ -1235,7 +1240,7 @@ OsReleaseSignals(void)
 {
 #ifdef SIG_BLOCK
     if (--BlockedSignalCount == 0) {
-        sigprocmask(SIG_SETMASK, &PreviousSignalMask, 0);
+        sigprocmask(SIG_UNBLOCK, &PreviousSignalMask, 0);
         OsReleaseSIGIO();
     }
 #endif

Works for for me too, whichever you prefer.

Cheers,
  Peter