TimeScheduler3

The current TimeScheduler2 class has a few deficiencies:

• taskReady() should only set next-execution-time if its argument is less than next-execution-time
• no_tasks: when setting this CAS, the result is only checked in 1 location, but not the other
• Potential loss of task: when calling schedule() on an existing Entry (same execution time), and - before adding the task to Entry - Entry is removed by _run() as it was executed, then the newly added task will never get to run !
• Simplification: instead of headMap(), just use firstEntry(), removeFirstEntry(). See pseudo code below.

As a workaround, timer_type="old" will switch back to the previous default timer. The reason for TimeScheduler3 (versus changing TimeScheduler2) is that we can simply switch to the new impl by setting (a new) timer_type="new2". Should this have a bug, we can simply switch back to "new" or "old" (or "wheel".

Over time, TimeScheduler2 will get removed.

Pseudo code:

• loop while has tasks
  • get the first task
  • if its time is less than the current time: execute it and remove it
  • else block (on the next task or 10s) until an element is added