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Marc A. Lehmann


Coro::LWP - make LWP non-blocking - as much as possible


 use Coro::LWP; # afterwards LWP should not block


This module tries to make LWP non-blocking with respect to other coroutines as much as possible, and with whatever means it takes.

LWP really tries very hard to be blocking, so this module had to be very invasive and must be loaded very early to take the proper effect.

Here is what it currently does (future versions of LWP might require different tricks):

It loads Coro::Select, overwriting the perl select builtin globally.

This is necessary because LWP calls select quite often for timeouts and who-knows-what.

Impact: everybody else uses this (slower) version of select, too. It should be quite compatible to perls builtin select, though.

It overwrites Socket::inet_aton with Coro::Util::inet_aton.

This is necessary because LWP might (and does) try to resolve hostnames this way.

Impact: likely little, the two functions should be pretty equivalent.

It replaces the base class of Net::HTTP, Net::FTP, Net::NNTP.

This is necessary because LWP does not always use select to see wether a filehandle can be read/written without blocking, so the base class IO::Socket::INET needs to be replaced by Coro::Socket.

Impact: Coro::Socket is not at all compatible to IO::Socket::INET. While it duplicates some undocumented functionality required by LWP, it does not have all the methods of IO::Socket::INET and might act quite differently in practise. Also, protocols other than the above mentioned will still block, at least some of the time.

All this likely makes other libraries than just LWP not block, but thats just a side effect you cannot rely on.

Increases parallelism is not supported by all libraries, some might cache data globally.


 Marc Lehmann <schmorp@schmorp.de>