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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.


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

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