DPU master thread dispatches one request at a time near the end of long files

[andradazoltan]

Priority: high

At the start of the program, the DPU master thread correctly dispatches multiple requests at a time. The size of each batch largely depends on how many upper-level threads are in the ORC parser, and should be close to that number. However, towards the end of the program the upper-level threads appear to get out of sync, resulting the the DPU master thread only dispatching one request at a time.

To observe this bug add two print statements:

• One in load_rank after each request's initial information is copied to the DPU
• One in unload_rank after each request's ID is copied back from the DPU

Towards the start of the program, the prints will appear as a batch of "load" followed by a batch of "unload", as desired. Towards the end of the program, the prints will appear as one "load" followed by one "unload" and so on.

This needs to be fixed in hopes of achieving an efficient implementation. It may require some updates to the scheduling policy to prevent it from getting into this state, or recover if it ever gets into this state.