See task_states.pdf

Explanation of states:

new:      start not called

ready:    task.start()/resume() called. Task is in the 
          scheduler q or has been taken out of it and handed to 
          the thread. Note that task.running = true (doesn't reflect
          the 'running' state below)
          
running:  stack is resumed. task runs normally to completion
          or until Task.pause/yield/exit is called.

pausing:  pause called with a PauseReason object
          pauseReason can be user-defined. Predefined ones are
          YieldReason, TaskDoneReason, Empty_MsgAvListener, 
          Full_SpcAvListener etc.

          Task.running remains true until it moves to paused state.

paused:   waiting for a message. 
          Task.running = false /\ Task.pauseReason.isValid()

done  :   task.execute() returned normally or with an unchecked exception
          or Task.exit() called

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Messages and task scheduling

What happens when a message arrives in each of the above states?

new: no scheduling on msgs. start() explicitly schedules the task whether
     or not there are mailboxes.

ready:
running:   
    no scheduling necessary when msg is put into mbox; task will rcv
    the message on get() The distinction between ready and running is
    not really important from a scheduling or message interaction
    perspective.

pausing: no scheduling yet, because the task is still unwinding,
    But after the task is fully unwound, it'll be scheduled again if there
    are messages in an mbox that caused that task to pause in the first
    place. 

paused: Schedule the task.