From: Corinna Vinschen <corinna-cygwin@cygwin.com>
To: cygwin@cygwin.com
Subject: Re: cygwin-2 process handling
Date: Wed, 27 May 2015 12:39:00 -0000 [thread overview]
Message-ID: <20150527122312.GF16927@calimero.vinschen.de> (raw)
In-Reply-To: <20150521205357.2c125b3bcaf877d0843b52b1@nifty.ne.jp>
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Hi Takashi,
On May 21 20:53, Takashi Yano wrote:
> [...]
> I was looking into this problem, and found the PeekNamedPipe()
> call is blocked in fhandler_pty_master::close() when the problem
> occurs.
>
> I had not noticed that,
>
> https://msdn.microsoft.com/en-us/library/windows/desktop/aa365779(v=vs.85).aspx
>
> says:
> > The PeekNamedPipe function can block thread execution the same
> > way any I/O function can when called on a synchronous handle in
> > a multi-threaded application.
>
> I have made a patch attached to resolve this problem. Please have
> a look.
>
> With this patch, NtQueryObject() is used instead of PeekNamedPipe()
> to detect closure of the last master handle.
>
> Please refer to the following discussion for more details.
> http://cygwin.com/ml/cygwin/2015-03/msg00221.html
>
>
> ChageLog is as follows.
>
> 2015-05-21 Takashi Yano <...>
>
> * fhandler_tty.cc (fhandler_pty_master::close): Use NtQueryObject()
> instead of PeekNamedPipe() to detect closing the last master handle.
> [...]
> + if (output_handle_local)
> + {
> + OBJECT_BASIC_INFORMATION obi;
> + NTSTATUS status;
> + ULONG hdl_cnt = 0;
> +
> + status = NtQueryObject (output_handle_local, ObjectBasicInformation,
> + &obi, sizeof obi, NULL);
> + if (!NT_SUCCESS (status))
> + debug_printf ("NtQueryObject: %y", status);
> + else
> + hdl_cnt = obi.HandleCount;
> + termios_printf("HandleCount: %d", hdl_cnt);
> + if (hdl_cnt == 1)
> + SetEvent (input_available_event);
> + CloseHandle (output_handle_local);
> + }
Isn't that racy? Consider two processes doing that at the same time.
Both calls to NtQueryObject could come up with hdl_cnt == 2 and the
problem persists.
Wouldn't it be safer to call SetEvent(input_available_event) all the
time from here?
Corinna
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Maintainer cygwin AT cygwin DOT com
Red Hat
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next prev parent reply other threads:[~2015-05-27 12:23 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-18 19:18 Michael Mauger
2015-05-19 17:36 ` Ken Brown
2015-05-20 1:19 ` Ken Brown
2015-05-21 12:13 ` Takashi Yano
2015-05-21 15:50 ` Ken Brown
2015-05-27 12:39 ` Corinna Vinschen [this message]
2015-05-27 15:57 ` Corinna Vinschen
2015-05-28 11:48 ` Corinna Vinschen
2015-05-28 12:44 ` Takashi Yano
2015-05-28 14:16 ` Takashi Yano
2015-05-28 15:53 ` Corinna Vinschen
2015-06-07 0:03 ` cygwin-2 process handling (about SIGHUP) Takashi Yano
2015-06-08 12:09 ` Corinna Vinschen
2015-06-08 13:50 ` Marco Atzeri
2015-06-08 14:18 ` Corinna Vinschen
2015-05-28 12:09 ` cygwin-2 process handling Takashi Yano
2015-05-22 17:34 Michael Mauger
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