s/memory/cpu/ noted...

The loop you show looks fine, but you understand that can_read(0) doesn't block? It returns immediately, whether any handles are ready or not. If the surrounding code is essentially:

while(1) {
    foreach $client ($select->can_read(0)) {
        dostuff
    }
}
[download]

then you're going to keep calling can_read() just as fast as you can, rather than truly blocking until a file handle becomes ready.

If you want can_read() to block as long as necessary, then you shouldn't pass a timeout argument. IF you need can_read() to return every so often, then you should pass some timeout other than 0. Only use 0 for the timeout if you don't want the call to block.