Removed the double circular link list to single.
Removed the double circular link list to single.

Rational:

1. Julia used to accumulate many events before scheduling the events
processing thread. Accumulation had to be carried out as a FIFO. With
thread sync now managed in OMP there is no need for large accumulation.
LIFO is ok as well.
2. If system starves the computation thread for any reason, the memory
footprint will not increase significantly if single linklist is used.

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