Refactor semaphore internals: make `_get_lease` synchronous (#3679)
Refactor semaphore internals: make `_get_lease` synchronous (#3679)

Co-authored-by: lr4d <a79f0485ef185645d4a05418ce2d8b0d88fb7434@users.noreply.github.com>
dask/distributed,blaze/distributed,dask/distributed,dask/distributed,dask/distributed,blaze/distributed