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