I posted this under a less suitable subject line a week ago, but I got no response. I hope the above live will trigger some help. I 've been doinking around with asio for a few weeks, and I've run into an issue I can't seem to wrap my head around. I've been playing with some code that originally was meant to pound a server with a large amount of packets for benchmarking purposes. It uses threads to launch hundreds of threads per second. When I replaced the old socket code with asio, and used a single io_service with run being called within each thread, I run out of file descriptors very quickly, and if I use a single io_service within each thread it's the same thing but the performance seems worse. Needless to say, this seems like a real limitation and I'm hoping I'm just being limited by my own misunderstanding, because I'm really enjoying the portability of asio. The docs that are there seem great, but there seems to be a lot more the library can do that I am missing out on, and I think the docs seem like they are not mentioning a lot of what asio an do. Can someone point me in the right direction for launching 1-to-N threads with a single send_to and a single receive_from within each thread that doesn't take the hit I'm seeing? It seems to me, that it's obvious that the io-service design is the difference, because I don't get the issue at all when I use plain old sockets, and the OS thread limit is then the only limitation. Any help would be greatly appreciated. FYI, I've done most of my experimenting on Linux and OSX. I can send some code samples if needed, but I think the problem should be apparent if anyone else has tried to use asio with large amounts of threads. Thanks, Pete