Re: stdio [de]merits discussion [Re: [musl] possible getopt stderr output changes]

[Laurent Bercot <ska-dietlibc@skarnet.org>]

On 11/12/2014 18:51, Rich Felker wrote:
> I like it because in all but the tiniest programs, you end up needing
> this kind of functionality, and whenever somebody rolls their own,
> it's inevitably 10x to 100x larger and uglier than musl's printf core.

  You haven't tried skalibs. ;)
  (Sure, calling format functions individually is far from being as
convenient, but the resulting code path is much shorter and there's
no bloat.)
  I agree we need standards. I just wish the existing standards were
better, and I don't want to be forced to use them.


> Of all that, the only thing contributing non-trivial size is floating
> point support.

  Yes, that's the main thing, but it's an important one: in system
programming, floating point operations are uncommon - someone who
cares about code size is probably not using floating points.


> For seekable files, ftello can tell you.

  Same thing: system programming is more about pipes and sockets than
seekable files. In applications that write files, the interesting
logic is probably not in the I/O, and they don't care.


> But it's perfectly usable for producing new output in
> cases where all write errors will simply result in failing the whole
> "make a file" operation.

  I agree.


> This is solved by fflush before fclose.

  I'm surprised that you of all people say this. What if another thread
writes to the FILE between the fflush and the fclose ? Granted, if the
situation arises, it's probably a programming error, but still, since
atomicity is a big thing for FILE, needing 2 operations instead of 1
doesn't scream good design.


> GNU software (gnulib in particular) likes to ignore this problem by poking
> at internals; we gave them an alternate solution with musl a couple
> years back just to avoid this. :(

  Jesus. And you still argue that it's a usable interface, if people have
to hack internal implementation details to get a simple readability
notification working ?


> For event-driven models, yes. For threaded models, it's quite usable
> and IMO it simplifies code by a a larger factor than the size it adds,
> in cases where it's sufficient.

  "If you can't write asynchronous code, use threads and write synchronous
code." :-Þ
  I agree that threads are a good paradigm to have, but the choice of
which model to use should not be dictated by the indigence of available
interfaces.


> The big thing it provides here is a standard point of synchronization
> for error messages in multithreaded programs. Otherwise there would be
> no lock for different library components to agree on to prevent
> interleaved error output.

  write() guarantees atomicity up to PIPE_BUF bytes. I have never seen
an stderr error message that was bigger than that.


> Yes and no. There are some things that could have been done better,
> and some backwards-compatible additions that could be made to make it
> a lot more useful, but I think stdio still largely succeeds in freeing
> the programmer from having to spend lots of effort on IO code, for a
> large class of useful programs (certainly not all, though!).

  I agree it's good enough for Hello World and applications that just
need very basic I/O. What irks me is that stdio sets a potential barrier
to designing better I/O interfaces, and people who need reliable I/O
management often still contort themselves to use stdio, and the results
are ugly. See the aforementioned gnulib case.

-- 
  Laurent