Implementation of Hybrid Logical Clocks.
This is based on the paper "Logical Physical Clocks and Consistent
Snapshots in Globally Distributed Databases". Provides a
strictly-monotonic clock that can be used to determine if one event
The main clock type.
A value that represents a logical timestamp.
A clock source that returns wall-clock in nanoseconds.
Describes the interface that the inner clock source must provide.