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Date: Fri, 12 Jul 2019 17:31:28 +0200
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: Kenton Varda <kenton AT cloudflare DOT com>
Cc: cygwin AT cygwin DOT com
Subject: Re: sigpending() incorrectly returns signals pending on other threads
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On Jul  6 15:46, Kenton Varda wrote:
> Hello Cygwin,
>=20
> According to the (Linux) man page: "sigpending() returns the set of
> signals that are pending for delivery to the calling thread"
>=20
> However, on Cygwin, sigpending() seems to return the set of signals
> pending on any thread, as shown in the attached test program.
>=20
> Among other things, this can cause deadlocks in programs which use
> sigpending() to check for pending signals, then use sigsuspend() to
> induce delivery of the specific signals that are pending. Because the
> signal is not actually pending on the current thread, sigsuspend()
> will unexpectedly block, potentially forever.
>=20
> Output of test program:
> $ uname -srv
> CYGWIN_NT-6.1 3.0.7(0.338/5/3) 2019-04-30 18:08
> $ gcc -std=3Dc11 -Wall test-sigpending.c -o test-sigpending -pthread &&
> ./test-sigpending
> sending signal to child thread with pthread_kill()...
> sigpending() says signal is pending in main thread (WRONG)
> sigpending() says signal is pending in child thread (CORRECT)
> received signal in child thread (CORRECT)

Thanks for the testcase.  This should work now in current git master.
I uploaded new developer snapshots to https://cygwin.com/snapshots/
Please give them a try.


Thanks,
Corinna

--=20
Corinna Vinschen
Cygwin Maintainer

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