Beefy Boxes and Bandwidth Generously Provided by pair Networks
We don't bite newbies here... much

Comment on

( #3333=superdoc: print w/replies, xml ) Need Help??

The problems (long term; I previously put it down to my not using the module correctly), I've been encountering with IO::Select come down to the fact that the module relies upon fileno to do its thing.

Where this falls down is if the handle gets closed before the program gets around to remove()ing it from the IO::Select object. For example, if you code:

... $client->close; $sel->remove( $client ); ...

You won't get any errors or warnings, but your server simply will not work correctly.

Because the socket was closed before it was removed, fileno( $client ) will return undef and the attempt to remove the handle from the select object fails. SILENTLY!

After that, pretty much nothing works properly.

I realise that the above code can be seen to be in error, and switching the order of the two statements makes it work. But that doesn't cover all the bases, because it is perfectly possible for a file handle to get closed without the program doing it explicitly.

This turns out to be a known problem that was reported in 2010, previously reported in 2005 and (apparently) probably existed since circa. 1998..

And, despite that the RT suggests a fix has been applied in May 2010, inspecting the CPAN source shows that it will still fail -- silently -- today.

Even a simple warning that you've made an attempt to remove a closed handle would help; but it isn't hard to fall back on a linear search of the array of file handles and relate their position in the array back to a fileno and hence bit vector bit.

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

RIP Neil Armstrong

In reply to Re: Does IO::Select work? (Problem partially resolved) by BrowserUk
in thread Does IO::Select work? Anywhere? by BrowserUk

Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":

  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?

    What's my password?
    Create A New User
    and all is quiet...

    How do I use this? | Other CB clients
    Other Users?
    Others pondering the Monastery: (3)
    As of 2018-01-24 00:51 GMT
    Find Nodes?
      Voting Booth?
      How did you see in the new year?

      Results (254 votes). Check out past polls.