CpSolverSolutionCallback and num_workers

[alireza...@gmail.com]

Hi Laurent, 

I have a simple CP model (/python3.10/dist-packages (9.9.3963)) as follows ( I need to find all solutions):

X1 + 2X2 + 3X3 =6 

it works fine but when I specify the number of num_workers

it does not work anymore 

Could you please advise ? 

Thanks in advance 

Alireza 

from ortools.sat.python import cp_model

class VarArraySolutionPrinter(cp_model.CpSolverSolutionCallback):

"""Print intermediate solutions."""

def __init__(self, variables):

cp_model.CpSolverSolutionCallback.__init__(self)

self.__variables = variables

self.__solution_count = 0

def on_solution_callback(self):

self.__solution_count += 1

print(f"---------Solution {self.__solution_count} ------------------")

for i,v in self.__variables.items():

print(i, self.Value(v) )

def solution_count(self):

return self.__solution_count

def main() -> None:

model = cp_model.CpModel()

N = 3

coef = [ 1,2,3]

x = {i:model.NewIntVar(0,3, f"x_{i}") for i in range(N)}

model.Add( sum( coef[i]*x[i] for i in range(N) ) == 6)

solver = cp_model.CpSolver()

#solver.parameters.num_workers = 4

solver.parameters.enumerate_all_solutions = True

solution_printer = VarArraySolutionPrinter(x)

status = solver.solve(model, solution_printer)

model.ExportToFile('simplemodel.txt')

if status == cp_model.OPTIMAL or status == cp_model.FEASIBLE:

print(f"Maximum of objective function: {solver.objective_value}\n")

else:

print("No solution found.")

if __name__ == "__main__":

main()

[Laurent Perron]

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Enumerating all solutions does not work in parallel. 

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