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X-HELO: calimero.vinschen.de
Date: Wed, 27 May 2015 17:17:34 +0200
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: cygwin-2 process handling
Message-ID: <20150527151734.GM16927@calimero.vinschen.de>
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On May 27 14:23, Corinna Vinschen wrote:
> Hi Takashi,
>=20
> On May 21 20:53, Takashi Yano wrote:
> > [...]
> > +  if (output_handle_local)
> > +    {
> > +      OBJECT_BASIC_INFORMATION obi;
> > +      NTSTATUS status;
> > +      ULONG hdl_cnt =3D 0;
> > +
> > +      status =3D NtQueryObject (output_handle_local, ObjectBasicInform=
ation,
> > +	  &obi, sizeof obi, NULL);
> > +      if (!NT_SUCCESS (status))
> > +	debug_printf ("NtQueryObject: %y", status);
> > +      else
> > +	hdl_cnt =3D obi.HandleCount;
> > +      termios_printf("HandleCount: %d", hdl_cnt);
> > +      if (hdl_cnt =3D=3D 1)
> > +	SetEvent (input_available_event);
> > +      CloseHandle (output_handle_local);
> > +    }
>=20=20
> Isn't that racy?  Consider two processes doing that at the same time.
> Both calls to NtQueryObject could come up with hdl_cnt =3D=3D 2 and the
> problem persists.
>=20
> Wouldn't it be safer to call SetEvent(input_available_event) all the
> time from here?

We discussed this already in March and only briefly talked about a
change like this requiring changes to fhandler_pty_slave::read.
However, I don't see this.  The read code already takes 0 bytes input
and broken pipe scenarios into account.  Do you see something needing
a change I don't?


Thanks,
Corinna

--=20
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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