This layer allows you to have a single- or multithreaded resource manager. This means that one thread can be handling a write() while another thread handles a read().
You provide the blocking function for the threads to use as well as the handler function that's to be called when the blocking function returns. Most often, you give it the dispatch layer's functions. However, you can also give it the resmgr layer's functions or your own.
You can use this layer independently of the resource manager layer.