Just like the thread stats and poll stats earlier, the queue stats
are now moved to worker.
A litte refactoring still, and the polling will only work on local
data.
Each worker now has a separate structure for collecting the
polling statistics that is passed to epoll_waitevents(). When
the stats are asked for, we loop over all separate stats and
combine them. So, instead of having every statistics of each
thread one cacheline apart, each thread has all its statistics
in one lump that, for obvious reasons, are going to be apart.
The primary purpose of this excersize is to remove the hardwired
nature of the statistics collection. For instance, the admin
thread will be doing I/O but that I/O should not be included
in the statistics of the workers.
The Worker no longer creates a pipe and implements the cross
worker/thread message mechanism itself. Instead it has a
MessageQueue instance variable for that purpose.
Now the epoll instance of the Worker is used when polling. The
work is still done in poll.cc and the worker provides the descriptor
and thread id.
The comments of poll_waitevents() have been removed; they were not
accurate anymore so better to let the code speak for itself.
And add the Worker header...
The epoll instance is not used yet, but the common creation of epoll
instances in poll.cc will be removed and the epoll instances of each
worker used instead.
This is the first step in turning the worker mechanism and everything
around it into a set of C++ classes. In this change, the original C
API is still present, but in subsequent changes that will be removed.
