Listen socket handles need to be week_ptr so that they can detect when a listen
socket is removed in the middle of a tracker announce on it. Use a wrapper class
to enforce that no one outside of session_impl can hold ownership of the socket
across event boundaries.
To support unit tests, listen_socket_t is also split into a base class which
holds the members needed to support the public listen socket API.
make the random function produce proper random distributions, based on uniform_int_distribution of C++11. also clean up piece_picker's priority_range to return two results instead of taking pointers to out-parameters. fix recent pe-crypto regression exposed by this change
While the simulation is single threaded, because async_receive_from_impl uses
post() to invoke the receive handler it is possible for multiple receive
handlers to be queued up in the io_service at the same time. If this happens
with a shared receive buffer the last packet received will overwrite all the
other packets before they are handled.
The use of post() is necessary to avoid unbounded recursion in the read handler
so each node must get its own buffer.
Steven Siloti