Threadpool does not complete a full cycle on quit

[ethanrublee]

The Threadpool scheduler, on ecto::QUIT, stops the graph prematurely. Notice how the Dealer has dealt 72 times, and everyone else less? People are loosing cards.

Module ecto::Dealer returned ecto::QUIT Stopping everything.
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*                 Cell Name   Calls   Hz(theo max) Hz(observed) load (%)
*              ecto::Dealer   72      79911.03     10.53        0.01    
*                 db_reader   71      10.57        10.39        98.25   
*                FPS drawer   70      511.46       10.24        2.00    
*             image display   69      113516.06    10.09        0.01    
*             depth display   70      623.07       10.24        1.64    
*              mask display   70      86160.40     10.24        0.01    
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