Re: sigpending() incorrectly returns signals pending on other threads

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

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On Jul 14 15:19, Houder wrote:
> On Fri, 12 Jul 2019 17:33:51, Corinna Vinschen  wrote:
> 
> > On Jul  6 19:15, Kenton Varda wrote:
> 
> > > I found a second problem which may or may not be related:
> 
> > > If two threads use pthread_kill() to send each other the same signal,
> > > such that the signal should be separately pending on both threads at
> > > the same time, only one of the two signals is actually queued. It
> > > seems that pthread_kill() is ignored if the same signal is already
> > > pending on some other thread.
> > 
> > The current signal mechanism in Cygwin only allows for a signal to be
> > queued once.  Changing that is a pretty ambitioned task, which I simply
> > don't have enought time for.  However, patches to change that are more
> > than welcome.
> 
> .. uhm, just a note in the interest of accuracy ...
> 
>  - standard signals (which include USRSIG1 and USRSIG2) are not queued
>    (traditional signal semantics)
>  - only real-time signals should be queued ...
> 
> The executive (cygwin1.dll) must maintain a record of the signals that
> are pending for the process as a whole,
>  as well as a record of the signals that are pending for each thread.

Yeah, the latter is missing so far.

> A call to sigpending() returns the union of the set of signals that are
> pending for the process
>  and those that are pending for the calling thread.
> 
> Source: 33.2.1 (How the Unix Signal Model maps to threads) of LPI.
> 
> Undoubtedly, the signal mechanism in Cygwin must be "adapted", but
> as far as I can tell, there is no requirement to "queue" any of the
> standard signals ...

I think queing here means just what you outline above.  It's kind of a
queue of pending signals and in Cygwin it's actually literally a queue.


Corinna

-- 
Corinna Vinschen
Cygwin Maintainer

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