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Date: Sun, 14 Jul 2019 15:19:17 +0200
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From: Houder <houder AT xs4all DOT nl>
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To: cygwin AT cygwin DOT com
Subject: Re: sigpending() incorrectly returns signals pending on other threads
References: <CAJouXQne09R+j+k+ZNw5fsZTFqDG5_9iwm9KQnxHoycL+ap_KQ AT mail DOT gmail DOT com> <CAJouXQksOsqWV=pVAJrXPn2FKtAyUO3QTxpugJ9R9rLGEN91UQ AT mail DOT gmail DOT com> <20190712153351 DOT GH3772 AT calimero DOT vinschen DOT de>
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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.

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 ...

Regards
Henri


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