| Clock | Interface for getting the current time. |
| MonotonicClock | A clock that is guaranteed not to go backward. |
| MonotonicNanoClock | A clock that is guaranteed not to go backward. |
| AwakeTimeSinceBootClock | A clock that returns number of milliseconds since boot. |
| CurrentThreadTimeClock | A clock that returns milliseconds running in the current thread. |
| RealtimeSinceBootClock | A clock that returns number of milliseconds since boot. |
| SystemClock | Implementation of Clock that delegates to the system clock. |