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


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


Over the years, a number of less-invasive alternatives have popped up, which you might find more acceptable than this rather invasive and fragile module. All of them only support HTTP (and sometimes HTTPS).


Works fine without Coro. Requires using a very different API than LWP. Probably the best choice iff you can do with a completely different event-based API.


Makes LWP use AnyEvent::HTTP. Does not make LWP event-based, but allows Coro threads to schedule unimpeded through its AnyEvent integration.

Lets you use the LWP API normally.


Basically the same as above, distinction unclear. :)


A different user agent implementation, not completely transparent to users, requires Coro.


This module is an AnyEvent user, you need to make sure that you use and run a supported event loop.

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 (and relies on a lot of undocumented functionality in IO::Socket), so this module had to be very invasive and must be loaded very early to take the proper effect.

Note that the module AnyEvent::HTTP might offer an alternative to the full LWP that is designed to be non-blocking.

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: some code might not expect coroutine semantics, for example, when you fork you might prefer the blocking variant because other coroutines shouldn't actually run.

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

This is necessary because LWP does not always use select to see whether 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 that's just a side effect you cannot rely on.

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


   Marc A. Lehmann <>