Asynchronous execution

minizinc(mzn, *dzn_files[, args, data, …])

Coroutine version of the pymzn.minizinc function.

PyMzn supports asynchronous solving through Python coroutines. The package pymzn.aio contains the coroutine version of the standard pymzn.minizinc function. This coroutine allows to execute the minizinc as an asynchronous process and to obtain intermediate solutions while the solver is still in execution. This is useful e.g. when the solver may take a long time to finish and one needs to keep track of the progress or when the number of returned solutions is very high, so the MiniZinc process does not have to keep the solutions in memory before the caller can start consuming them.

To use the minizinc coroutine, you need to have an event loop running in the main thread of your application. Awaiting the minizinc coroutine produces a lazy solution stream that, when addressed or iterated over returns all the solutions found so far by the solver. The following is a full example of how to use the minizinc coroutine:

async.mzn
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% Use a large domain to simulate a long solving process
var 0 .. 100000: x;
solve satisfy;
async.mzn
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import pymzn
import asyncio
from pymzn.aio import minizinc

async def main():
    solns = await minizinc('async.mzn', all_solutions=True, keep_solutions=False)
    while solns.status is not pymzn.Status.COMPLETE:
        await asyncio.sleep(1)
        for i, soln in enumerate(solns):
            if i == 0:
                print(soln)

asyncio.run(main())

This code will execute the main coroutine, which calls minizinc to find all solutions of the async.mzn file. The option keep_solutions is set to False to avoid saving the solutions in memory. Each time the solns object is iterated over, it will return all the solutions found until that point. Between iterations, a period 1 second is waited to simulate other work performed on the main thread.