Re: Help: looking for equivalent syscall to shutdown() but for unix pipes

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

On 18/01/2019 08:11, Florian Weimer wrote:
> * Alexandre Bique:
> 
>> On Thu, Jan 17, 2019 at 9:48 AM Florian Weimer <fweimer@redhat.com> wrote:
>>>
>>> * Alexandre Bique:
>>>
>>>> I'm having an issue with pipes in a multi-threaded application.
>>>>
>>>> I have one thread (T1) reading a pipe in a loop, and I'd like to close
>>>> that pipe from an other thread (T2) and join T1.
>>>>
>>>> With sockets I'd use shutdown(fd, SHUT_RD).
>>>
>>> I don't think something like this exists for pipes.
>>>
>>>> What do you recommend?
>>>
>>> You need some sort of framing layer, so that you can transmit both data
>>> and an EOF indicator.
>>
>> Thank you very much.
>>
>> I'm not very enthusiast with the idea of sending an EOF message,
>> because the original producer comes from an other process, so there
>> could be all sorts of corrupted data over the pipe, unless maybe it is
>> using packets instead of streams. But in our case it is using streams.
>>
>> I was thinking that I could use poll on the file descriptor and then
>> just check a flag before reading the pipe. Now to wake up the poll()
>> syscall I would need an eventfd which is an additional opened file,
>> not awesome.
> 
> How do you detect that you are at the end of the stream if you do not
> have an EOF indicator?  If the other process crashes for any reason, you
> are left with truncated data if you don't have an EOF indicator.
> 
> In the past, I dealt with the crash problem by launching the producer
> process from the consumer, and commit to processing the data in the
> consumer only after the producer has exited with zero status.  Maybe
> that's an approach you could use?
> 
> Thanks,
> Florian
> 

Maybe use socketpair if unidirectional is not required?