* Fixes lock, and the underlying keepalive implmentation.
The previous implementation is buggy when a lot of locks happen at the same time,
as the cpprestsdk's threadpool use a fixed number of thread for posix platform:
https://github.com/microsoft/cpprestsdk/blob/master/Release/src/pplx/threadpool.cpp#L198
Signed-off-by: Tao He <sighingnow@gmail.com>
* Handling (or checking) possible failure in lease's KeepAlive.
* Add documentation.
* Enhance documentations.
Signed-off-by: Tao He <sighingnow@gmail.com>