Adding an example of a dedicated ST EC dispatching to a MT EC

[beta-ziliani]

Benchmarks (all of them with 30s and 40 connections):

• wrk running 2 threads, default workers (4), 1000 bytes request

preview_mt:
  Requests/sec:  79505.69
  Transfer/sec:     82.72M
ec:
  Requests/sec:  64983.74
  Transfer/sec:     67.61MB

• wrk running 2 threads, 8 workers, 1000 bytes request

preview_mt:
  Requests/sec:  73082.06
  Transfer/sec:     76.04MB
ec:
  Requests/sec:  86116.64
  Transfer/sec:     89.60MB 

• wrk running 4 threads, 6 workers, 4000 bytes request

preview_mt:
  Requests/sec:  44979.04
  Transfer/sec:    175.48MB
ec:
  Requests/sec:  45267.99
  Transfer/sec:    176.61MB

[ysbaddaden]

I recall an attempt to isolate the http server to its own thread didn't fare well with preview_mt, but it's apparently working a little better with EC.

Now, wrk keeps the connections alive, so the dispatch only happens at the beginning, then everything happens in the MT context while the ST context sleeps. It could be interesting to have another client that regularly closes & reconnects the connections (e.g. every dozen ones).

[beta-ziliani]

In the last commit I separated the main thread only when running -Dec (no -Dmt).