Quick though (last one I promise):

Maybe put() could have an argument to indicate whether to be thread-blocking (i.e. guaranteeing the object to be sent in its current state) or not. The (current) non-thread-blocking mode will have better performance for the put()-calling process if there are a lot of processes trying to write to the queue at once since it can continue regardless (while the _feed thread waits for the internal Pipe to become available).