Task A
Task B
Task C
Task D
Task E
_wait Adding done callback
_wait Adding done callback
_wait Adding done callback
_wait Adding done callback
_wait Adding done callback
_wait Removing done callback
_wait Removing done callback
_wait Removing done callback
_wait Removing done callback
_wait Removing done callback
_wait returning 1 done, 4 pending
_wait Adding done callback
_wait Adding done callback
_wait Adding done callback
_wait Adding done callback
_wait Removing done callback
_wait Removing done callback
_wait Removing done callback
_wait Removing done callback
_wait returning 1 done, 3 pending
_wait Adding done callback
_wait Adding done callback
_wait Adding done callback
_wait Removing done callback
_wait Removing done callback
_wait Removing done callback
_wait returning 1 done, 2 pending
_wait Adding done callback
_wait Adding done callback
_wait Removing done callback
_wait Removing done callback
_wait returning 1 done, 1 pending
_wait Adding done callback
_wait Removing done callback
_wait returning 1 done, 0 pending