TODO

/* TODO(benh): Improve link/connection management. For example, make
   links be about sockets. Then see whether or not already connected
   sockets can be used for sending a message back (without opening a
   new socket first). */

/* TODO(benh): When a link fails, try and reconnect a configurable
   number of times before you just assume the link is dead. */

/* TODO(benh): Fix link functionality (processes need to send
   process_exit message since a dead process on one node might not
   know that a process on another node linked with it). */

/* TODO(benh): What happens when a remote link exits? Do we close the
   socket correclty?. */

/* TODO(benh): Handle/Enable forking. */

/* TODO(benh): Use multiple processing threads (do process affinity). */

/* TODO(benh): Better error handling (i.e., warn if re-spawn process
   instead of just returning bad pid). */

/* TODO(benh): Use different backends for files and sockets. */

/* TODO(benh): Allow messages to be received out-of-order (i.e., allow
   someone to do a receive with a message id and let other messages
   queue until a message with that message id is received).  */

/* TODO(benh): LinkManager::link and LinkManager::send are pretty big
   functions, we could probably create some queue that the I/O thread
   checks for sending messages and creating links instead ... that
   would probably be faster, and have less contention for the mutex
   (that might mean we can eliminate contention for the mutex!). */