[PATCH] chgserver: create new process group after fork (issue5051)

[Jun Wu]

Just found setpgrp is in Python std lib. Will update the patch.

On 01/19/2016 06:24 PM, Jun Wu wrote:
> # HG changeset patch
> # User Jun Wu <quark at fb.com>
> # Date 1453227613 0
> #      Tue Jan 19 18:20:13 2016 +0000
> # Node ID 2f7c73708d285349652b72ac774727ef2f0ebc84
> # Parent  d2c5ad3deccb5a504e2553652b66a4110db68afb
> chgserver: create new process group after fork (issue5051)
>
> This is to make SIGTSTP work. Before the patch, the server process group is
> considered "orphaned" and will ignore SIGTSTP, SIGTTIN, SIGTTOU, according to
> POSIX. See the comment above `will_become_orphaned_pgrp` in `kernel/exit.c`
> from Linux 4.3 for details.
>
> SIGTSTP is important if chgserver runs some ncurses commend like `commit -i`.
> Ncurses has its own SIGTSTP handler which will do the following:
>
>    1. Clean the screen
>    2. Stop itself by resending SIGTSTP to itself
>    3. Restore the screen
>
> If SIGTSTP is ignored, step 2 will be a noop, which means the process cannot
> be suspended properly.
>
> In order to make things work, chg client needs to forward SIGTSTP and SIGCONT
> to server as well.
>
> diff --git a/hgext/chgserver.py b/hgext/chgserver.py
> --- a/hgext/chgserver.py
> +++ b/hgext/chgserver.py
> @@ -29,6 +29,7 @@
>   from __future__ import absolute_import
>
>   import SocketServer
> +import ctypes, ctypes.util
>   import errno
>   import os
>   import re
> @@ -353,7 +354,13 @@
>
>   # copied from mercurial/commandserver.py
>   class _requesthandler(SocketServer.StreamRequestHandler):
> +    _libc = ctypes.CDLL(ctypes.util.find_library('c'), use_errno=True)
> +
>       def handle(self):
> +        # use a different process group from the master process, making this
> +        # process pass kernel "is_current_pgrp_orphaned" check so signals like
> +        # SIGTSTP, SIGTTIN, SIGTTOU are not ignored.
> +        self._libc.setpgid(0, 0)
>           ui = self.server.ui
>           repo = self.server.repo
>           sv = chgcmdserver(ui, repo, self.rfile, self.wfile, self.connection)
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