[PATCH v3 1/3] POSIX Asynchronous I/O support: aio files

[Corinna Vinschen]

Mark,

I think there's a bug in sigtimedwait.  I just found the problem while
looking into this aio_suspend stuff:

On Jul 17 16:51, Corinna Vinschen wrote:
> > +  res = sigtimedwait (&sigmask, &si, to);

You're giving the timeout value verbatim to sigtimedwait().

Let's have a look into sigtimedwait, per your original patch, commit
24ff42d79aab:

+  if (timeout)
+    {
+      if (timeout->tv_sec < 0
+           || timeout->tv_nsec < 0 || timeout->tv_nsec > (NSPERSEC * 100LL))
+       {
+         set_errno (EINVAL);
+         return -1;
+       }

So we're enforcing a positive timeout value.

+      /* convert timespec to 100ns units */
+      waittime.QuadPart = (LONGLONG) timeout->tv_sec * NSPERSEC
+                          + ((LONGLONG) timeout->tv_nsec + 99LL) / 100LL;
+    }

...which is converted to a likewise positive 100ns interval ...

+  return sigwait_common (set, info, timeout ? &waittime : cw_infinite);

...given to sigwait_common, which in turn calls

  cygwait (NULL, waittime, [flags])

cygwait uses this waittime value verbatim in a call to

  NtSetTimer (_my_tls.locals.cw_timer, timeout, [...]);

So NtSetTimer is called with a *positive* waittime value, right?

A positive value given to NtSetTimer is evaluated as a timestamp,
*not* as a time interval.  Look at the lpDueTime description of
SetWaitableTimerEx.  That's the WIN32 API function exposing the
NtSetTimer function:
https://docs.microsoft.com/en-us/windows/desktop/api/synchapi/nf-synchapi-setwaitabletimerex

However, the POSIX description of sigtimedwait indicates that the
timespec value is evaluated as a time interval, which is a relative
time:

http://pubs.opengroup.org/onlinepubs/9699919799/functions/sigtimedwait.html

So bottom line is, shouldn't timeout be converted to a negative waittime
value in sigtimedwait?


Thanks,
Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat
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