ector sw uses thread pool internally to process rle job parallel.
First of all, we lost task handles which allocated to each threads,
we must free the task data after thread done.
Secondly, tasks can be managed by one shape instance,
the instance can't catch upon multiple instances alive.
only last task can be attached to the shape instance.
Thus, obvisouly the instance doesn't expect to handle multiple tasks
at the same time, one instance only take care of one task on threading pool.