TimeService

New service which provides wall clock time at a coarse (configurable) granularity.

Motivation: System.currentTimeMillis() or System.nanoTime() is sometimes called frequently, e.g. by TCPConnectionMap$TCPConnection.updateLastAccessed() or in FD/FD_ALL. This has a cost, especially when a lock is held (system calls while a lock is held cause preemption and the thread losing its time slice).
However, the 2 examples above don't need the exact time, but an approximation of it is OK.

GOALS:

• Provide a time service which returns the last cached value of System.timeCurrentMillis()
• This is a quick and efficient call
• TimeService registers a timer task which updates its internal cached value every N milliseconds (configurable), e.g. every 500 ms

BENEFIT:
For example, in TCPConnection, the timestamp is updated whenever we send or receive a message from the peer. The timestamp is used to expire and close a connection (if configured), and can be updated 100'000 times a second. If the time service provided the current time in ms every 500ms, then System.currentTimeMillis() would only be called 2 times during a second instead of 100'000 times !