How to do a production scheduling with preemption (SRPT)?

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Amandine P asked Aug 12, '19 Amandine P commented Aug 19, '19

How to do a production scheduling with preemption (SRPT)?

Hello!

I’m trying to simulate production with arrival schedule and arrival time different to zero. I want that schedule follow the SRPT rule that is the shortest remaining processing time. Therefore, if a product is in production on the machine 1 and another product with a smaller processing time than the processing time remaining on the current product, the production of the latter is stopped and the new replaces it.

I don’t know how to do it, I have tried with process flow but without result.

Could you help me?

Thanks,

preemption production schedule

Answer 1 · 2019-08-13T12:29:57Z

Clair A answered Aug 13, '19 Amandine P commented Aug 19, '19

Hi @Amandine P,

I have built a sample model 2019-08-13-shortest-remaining-processing-time-srpt.fsm based on this arrival schedule:

(source: https://en.wikipedia.org/wiki/Shortest_remaining_time)

I used a Basic Processor logic as a starting point:

To build some kind of SRPT process flow:

The item trace gantt chart shows the same results as the wikipedia example:

Product #6 has been preempted twice by a product with a shorter remaining processing time.

The key behind the logic is a list with all products:

To find the product with the shortest remaining processing time, the query is:

ORDER BY RemainingTime ASC

Hope this helps.

shortest-remaining-time.png (18.2 KiB)

1-basic-processor.png (11.9 KiB)

srpt.png (27.9 KiB)

itemtracegantt.png (12.4 KiB)

list.png (5.4 KiB)

pullfromlist.png (6.0 KiB)

2019-08-13-shortest-remaining-processing-time-srpt.fsm (41.2 KiB)

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Amandine P commented · Aug 19, 2019 at 08:19 AM

@Clair A

Thank you very much,that's what I want! But I don't have the same version of FlexSim, I have version 16.2 and I can't find the right function for expression in ItemList1.

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itemlist1.png (26.0 KiB)

Clair A Amandine P commented · Aug 19, 2019 at 08:27 AM

Why are you using such an old version of the software ? I do recommend to update to the latest release.

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Amandine P Clair A commented · Aug 19, 2019 at 09:06 AM

Because I have the license for this version.

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