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Date: Tue, 11 Oct 2005 17:51:00 +0300
From: Pavel Tsekov <ptsekov AT gmx DOT net>
To: cygwin AT cygwin DOT com
Subject: Re: handle_threadlist_exception: handle_threadlist_exception called    with threadlist_ix -1
In-Reply-To: <Pine.CYG.4.58.0510061840550.1524@mordor>
Message-ID: <Pine.CYG.4.58.0510111733550.1460@mordor>
References: <SERRANOzGZuNY1SWoBD0000004f AT SERRANO DOT CAM DOT ARTIMI DOT COM>  <20050901144331 DOT GH18595 AT trixie DOT casa DOT cgf DOT cx> <Pine DOT CYG DOT 4 DOT 58 DOT 0510061616570 DOT 1556 AT mordor>  <20051006141933 DOT GB17445 AT trixie DOT casa DOT cgf DOT cx> <Pine DOT CYG DOT 4 DOT 58 DOT 0510061735120 DOT 1140 AT mordor>  <20051006150019 DOT GA6197 AT trixie DOT casa DOT cgf DOT cx> <Pine DOT CYG DOT 4 DOT 58 DOT 0510061840550 DOT 1524 AT mordor>
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On Thu, 6 Oct 2005, Pavel Tsekov wrote:

> On Thu, 6 Oct 2005, Christopher Faylor wrote:
>
> > >It might be a different problem but the message is the same.
> >
> > It *is* a different problem.
>
> Ok.
>
> > Some thread is sending a signal 31 (SIGUSR1).  Which thread is doing this?
>
> An application thread signaling another thread to stop its execution. I am
> on it - I'll report back if I manage to find something.

While tracking this problem I found what I suspect is a small bug in
the way sigsuspend() works when it is used to retrieve the list of pending
signals for a thread other than the main one. I think this is related to
the crash I am seeing in some way though this has to be determined yet.

As I read the code, when retrieving the list of pending signals
sigpending() inspects only the list of blocked signals for the main
thread - it doesn't look in the thread specific list of blocked signals
of the calling thread.

The code which I refer to is the following block from wait_sig():

        case __SIGPENDING:
          *pack.mask = 0;
          unsigned bit;
          sigq.reset ();
          while ((q = sigq.next ()))
            if (myself->getsigmask () & (bit = SIGTOMASK (q->si.si_signo)))
              *pack.mask |= bit;
          break;

On the other hand the code in sigpacket::process() does the right thing
when it delivers a signal i.e. it looks the list of blocked signals in
both the main thread and the target thread.

Attached is a simple test case which demonstrates the problem.

On Linux:

pending_set = 00000000
pending_set = 00000000
pending_set = 00000000
pending_set = 00000000
pending_set = 00000000
pending_set = 00000800
exiting thread_loop()

On Cygwin:

pending_set = 00000000
pending_set = 00000000
pending_set = 00000000
pending_set = 00000000
pending_set = 00000000
pending_set = 00000000
pending_set = 00000000
pending_set = 00000000
pending_set = 00000000
pending_set = 00000000
pending_set = 00000000
pending_set = 00000000
pending_set = 00000000

[ keeps looping forever ]
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