Why would it not be possible? "Server" and "client" aren't magic words, they're descriptions of roles.

Once you're over the learning curve POE would make something like this trivial, but there's nothing preventing you from doing something like this using select (or IO::Select) directly yourself either.

There are many ways to do this. Which is most appropriate really depends upon the nature of the logic involved.

For example, if the conversations with each of the servers is complex and mostly independant of the other, with only the occasional need to share state, then putting each in it's own thread and sharing state through a queue or shared variables may be the simplest approach.

If however, the conversations are highly interdependant with each driving the other, then the select approach makes more sense.

Each approach has both advantages and caveats. The right choice depends entirely upon the nature of the application.

The "as conditions require" part of your problem is implemented by the select function call. The difficulty with select-based approaches is that all of you logic is "turned inside-out". Modules like POE or even using threads make it easier to write your application logic at a small performance penalty (and learning curve to learn how to use POE.) On the other hand, it is helpful to learn how to multiplex I/O using select so that you have a better understanding of what is really going on when using something like POE.