don't leave the loop if select returned because the timeout expired

but no data is available yet
count requests per client as well as the total per process

and don't queue more than 512 requests when using pipelining

(probably such a low number of requests is limiting performances,
 so a test allowing more pipelined requests would be interesting)
count the number of requests queued in a connection context

and stop reading input data if we have more than 512 queued requests to handle

(NOTE: the limit needs probably to be tuned to ensure the best performances)