module Make_suspension_resistant: 
functor (P : PCLOCK) -> 
functor (M : MCLOCK) -> 
functor (MT : MTICK) -> 
functor (E : LIFECYCLE) -> WATCHER_FUN 

Best-effort, program suspension resistant, monotonic, clock tick watchers.

Given a watcher w:

• If there is no Tick.LIFECYCLE.suspend event while Tick.WATCHER.waiting w is true, the value of Tick.WATCHER.linger_ns w is an accurate and exact wall-clock time span.
• If there is one or more pairs of Tick.LIFECYCLE.suspend and Tick.LIFECYCLE.resume events while Tick.WATCHER.waiting w is true and that the difference between the value of Tick.PCLOCK.now_d_ps at these events provides an accurate measure of the actual wall-clock time span that elapsed during suspension, the value of Tick.WATCHER.linger_ns w is an accurate and exact wall-clock time span.

  This condition is typically satisfied if Tick.PCLOCK is well synchronized at Tick.LIFECYCLE.suspend and Tick.LIFECYCLE.resume and no leap second occurs between these two events. The absolute value of Tick.PCLOCK doesn't matter.

• Watcher triggers being functions they are not persisted and do not survive a Tick.LIFECYCLE.poweroff event.

type t 

type trigger = t -> unit 

include Tick.WATCHER