Path: csiph.com!goblin1!goblin.stu.neva.ru!usenet.stanford.edu!not-for-mail
From: Denys Vlasenko <dvlasenk@redhat.com>
Newsgroups: gnu.bash.bug
Subject: Re: "wait" loses signals
Date: Mon, 24 Feb 2020 18:19:46 +0100
Lines: 22
Approved: bug-bash@gnu.org
Message-ID: <mailman.1505.1582564797.2412.bug-bash@gnu.org>
References: <dab35be8-4b56-5887-bfa4-37ea7383864a@case.edu> <750d460d-b8a4-4157-1488-9f4d9f973715@redhat.com> <35034c85-fd5a-5034-a2d5-e3903888069d@case.edu> <cf7adbec-e705-1071-34e1-50f8188f0edc@redhat.com> <d60f1dbc-990d-7291-e075-b67c07f61a86@case.edu> <00620c20-19ea-e71e-dc1b-926847901f82@redhat.com> <25750.1582534783@jinx.noi.kre.to> <96ce0406-36fd-f93e-6ebc-49bd58b52148@case.edu> <a7e82b8b-046e-dbac-2f10-3f4dcac69f72@redhat.com>
NNTP-Posting-Host: lists.gnu.org
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Cc: Harald van Dijk <harald@gigawatt.nl>, Daniel Colascione <dancol@google.com>, bug-bash@gnu.org
To: chet.ramey@case.edu, Robert Elz <kre@munnari.OZ.AU>
Envelope-to: bug-bash@gnu.org
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0
In-Reply-To: <96ce0406-36fd-f93e-6ebc-49bd58b52148@case.edu>
Content-Language: en-US
Precedence: list
Xref: csiph.com gnu.bash.bug:15963

On 2/24/20 5:18 PM, Chet Ramey wrote:
> The first case is trickier: there's always going to be a window between
> the time the shell checks for pending traps and the time the wait builtin
> starts to run. You can't really close it unless you're willing to run the
> trap out of the signal handler, which everyone agrees is a bad idea, but
> you can squeeze it down to practially nothing.

dash uses something along these lines:

         sigfillset(&mask);
         sigprocmask(SIG_SETMASK, &mask, &mask);
         while (!pending_sig)
                 sigsuspend(&mask);
         sigprocmask(SIG_SETMASK, &mask, NULL);
         if (pending_sig)
                 handle_signals(pending_sig);
         pid = waitpid(... WNOHANG);

It sleeps in sigsuspend(), not in waitpid(). This way we wait for both
signals *and* children (by virtue of getting SIGCHLD for them).