From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:47667)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <paolo.bonzini@gmail.com>) id 1VgCtq-0000sO-8l
	for qemu-devel@nongnu.org; Tue, 12 Nov 2013 07:17:02 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <paolo.bonzini@gmail.com>) id 1VgCth-0000xE-SV
	for qemu-devel@nongnu.org; Tue, 12 Nov 2013 07:16:54 -0500
Received: from mail-ea0-x22e.google.com ([2a00:1450:4013:c01::22e]:47848)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <paolo.bonzini@gmail.com>) id 1VgCth-0000wk-Lo
	for qemu-devel@nongnu.org; Tue, 12 Nov 2013 07:16:45 -0500
Received: by mail-ea0-f174.google.com with SMTP id n15so2832466ead.33
	for <qemu-devel@nongnu.org>; Tue, 12 Nov 2013 04:16:44 -0800 (PST)
Sender: Paolo Bonzini <paolo.bonzini@gmail.com>
Message-ID: <52821C29.5020005@redhat.com>
Date: Tue, 12 Nov 2013 13:16:41 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
MIME-Version: 1.0
References: <1384245814-15010-1-git-send-email-kraxel@redhat.com>
	<528216C7.10705@redhat.com>
In-Reply-To: <528216C7.10705@redhat.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH] curses: fixup SIGWINCH handler mess
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Laszlo Ersek <lersek@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>, Anthony Liguori <aliguori@amazon.com>, qemu-devel@nongnu.org

Il 12/11/2013 12:53, Laszlo Ersek ha scritto:
> Also, I grepped the source for SIGWINCH, and I think it is never masked
> with pthread_sigmask(), or -- while the process is single-threaded
> initially -- with sigprocmask(). Hence this signal can be delivered at
> any time and interrupt interruptible functions (which is good
> justification for the patch.) My point though is that after this patch a
> narrow window seems to exist where you can lose a signal, namely between
> checking "got_sigwinch" and resetting it.

You don't really lose it, it is delayed to the next refresh.

> (SIGWINCH is not a standard signal but I do think it it's not a realtime
> one, hence it doesn't queue up; it can only be pending or not.)

Indeed.

> For ultimate pedantry we could maybe write
> 
>     bool local;
> 
>     /* block the signal with pthread_sigmask()
>      * for atomic retrieval and reset
>      */
>     local = got_sigwinch;
>     got_sigwinch = false;
>     /* unblock the signal */
> 
>     if (!local) {
>         return;
>     }
> 
> but it's likely overkill.

Or just use an atomic function:

    if (!atomic_xchg(&got_sigwinch, false)) {
        return;
    }

Paolo