Date: Tue, 4 Oct 2011 12:39:34 -0400
From: Christopher Faylor <cgf-use-the-mailinglist-please AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: 1.7.9 Missing SIGPIPE?
Message-ID: <20111004163934.GA30117@ednor.casa.cgf.cx>
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On Tue, Oct 04, 2011 at 04:33:33PM +0200, Marco Atzeri wrote:
>On 10/4/2011 4:09 PM, Christopher Faylor wrote:
>> On Tue, Oct 04, 2011 at 04:00:13PM +0200, Marco Atzeri wrote:
>>> On 10/4/2011 3:53 PM, Peter Rosin wrote:
>>>> Peter Rosin skrev 2011-09-28 17:26:
>>>>> Hi!
>>>>>
>>>>> When I use bash to build pipelines, they sometimes don't finish but
>>>>> instead some process remains running. Example:
>>>>>
>>>>> $ tail -f -n 10000 log.txt | grep . | head -n 2
>>>>>
>>>>> Almost instantly I get the expected two lines of output, but no prompt
>>>>> back. I have to use ctrl-c. If I don't ctrl-c I can run pstree in
>>>>> another terminal and see this:
>>>>>
>>>>> $ pstree
>>>>> ??????????mintty?????????bash?????????tail
>>>>>     ??????mintty?????????bash?????????pstree
>>>>
>>>> This example is a poor one, as tail simply waits for a new line, when it
>>>> gets a new line it forwards it to the pipe and promptly receives a
>>>> SIGPIPE as grep is not there anymore.
>>>>
>>>> I'll get back when I have distilled a better STC. If I can...
>>>
>>> Hi Peter,
>>> are you referring on something like SIGHUP on PTY closure ?
>>>
>>> http://cygwin.com/ml/cygwin/2011-07/msg00295.html
>>> http://pubs.opengroup.org/onlinepubs/9699919799/functions/close.html
>>
>> Note that this thread contains your assertion that something isn't
>> happening correctly but it isn't clear that your analysis is correct.
>>
>> But, no, SIGPIPE != SIGHUP and the above example clearly shows a
>> completely different scenario than what is described in the above
>> thread.
>>
>> cgf
>
>Hi Cgf,
>I know that SIGPIPE != SIGHUP, but Peter mentioned that the example
>is not really representative of the PIPE problem he found, so eventually
>he catched the same problem I saw on mc.
>Of course, it could be a different one.
>
>Referring to the SIGHUP thread
>This portion of the standard, if I am not wrong,
>it is not currently implemented in cygwin:
>
>"If fildes refers to the master side of a pseudo-terminal, and this is 
>the last close, a SIGHUP signal shall be sent to the controlling 
>process, if any, for which the slave side of the pseudo-terminal is the 
>controlling terminal. It is unspecified whether closing the master side 
>of the pseudo-terminal flushes all queued input and output."

As I mentioned in the thread, that is supposed to be implemented in
Cygwin.  I could never see a case where it wasn't sent.

cgf

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