Support for Pluggable I/O Polling

[ghost]

Default connection implementation is using poll/WSAPoll functions for waiting connection socket to become readable/writable. While this approach works perfectly fine, it does not allow client application to do something else while waiting for connection socket.

In this pull request, I have introduced an abstract base class custom_io_poller, where concrete implementations of this class is responsible for monitoring a socket with timeout. Each connection keeps a pointer to the associated I/O poller, which is set to nullptr by default. On each invocation of connection::wait, connection will either call external I/O poller or poll the socket by itself.

This would make it possible to integrate taoPQ with Asio/Boost.Asio or similar async I/O frameworks. Could you consider adding such custom polling support to taoPQ prior to first public release?

Thanks.

[d-frey]

Looks interesting, but I think the implementation could probably be improved a bit, unifying it with the existing poll implementation. I will have a look when I have more time.

[d-frey]

I committed a more general version, putting the existing poll implementation(s) into a default_poll callback that you can overwrite. You can also set your own callback for a connection pool, which will then be used for all connections opened by the pool. Let me know if this works for you or if you have any other feedback.

[ghost]

Hello,

I think your version is fine too for general use. But it looks like "include/tao/pq/poll.hpp" is missing from the commit.

Thank you.

[d-frey]

My bad, I forgot the git add ... - should be fixed now.