[nanomsg] Re: On the use of small integers instead of pointers to identify "sockets"
- From: luca barbato <luca.barbato@xxxxxxxxxxx>
- To: nanomsg@xxxxxxxxxxxxx
- Date: Thu, 5 Sep 2013 09:53:06 +0200
On Thu, Sep 5, 2013 at 7:03 AM, Martin Sustrik <sustrik@xxxxxxxxxx> wrote:
> On 04/09/13 17:50, Nico Williams wrote:
>
>> But surely nanomsg fd numbers can't be passed to POSIX system calls and
>> library functions!
>
>
> No. You can't implement that in user space. POSIX doesn't allow for that
> kind of thing. True file descriptors can be implemented only in the kernel
> space.
>
> However, I've made a patch for Linux kernel that would fix that and allow
> for implementing true fds in the user space. Unfortunately, I don't have
> enough time and morale to push the patch to the mainline.
>
>
>> Or did I miss something? Perhaps you're just trying to
>> match POSIX system call prototypes [for some reason that I missed]?
>
>
> Yes. The goal is not to force developers to memorise two slightly different
> sets of APIs. ZeroMQ have diverged that way lately -- the API is kind od
> socket-like, but there's a lot of differences as well. If you are working
> with both APIs you have to do a lot of mental switching which is not very
> helpful.
>
>
>>> Btw, one minor, but nice feature of ints as socket handles is that you
>>> can close a socket, then try to use it and get EBADF error. In ZeroMQ,
>>> where I've used pointers as handles, your program just crashes.
>>
>>
>> Er, yes, but since usually the next fd allocated is the lowest non-
>> negative number not currently in use... you could end up (particularly
>> in threaded programs, but not only) writing to the wrong fd. The same
>> could happen if you used pointers, of course, but the point is that bugs
>> are bugs, and [likely] crashing is better than [possible] silent
>> corruption.
>
>
> True. Both ways are deficient. I guess matter of personal preference in the
> end.
I guess if somebody volunteers to provide a pointer-API for nanomsg
nobody would kill the project.
lu
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