[BUG] Pure virtual method called when using `BatchSolve(...)`

[araml]

When running batch solve after setting the variables to CONTINUOUS you get eventually a pure virtual method called with termination

Steps/Code to reproduce bug

This snippet reproduces it on my machine pretty often, using flugpl which is a very small MIP problem https://miplib.zib.de/instance_details_flugpl.html

import numpy as np

import cuopt_mps_parser
from cuopt.linear_programming.problem import CONTINUOUS, solver
from cuopt.linear_programming.solver_settings import SolverSettings
from cuopt.linear_programming.solver.solver_parameters import (
    solver_params,
    CUOPT_ABSOLUTE_DUAL_TOLERANCE,
    CUOPT_PDLP_SOLVER_MODE,
    CUOPT_PRESOLVE
)
from cuopt.linear_programming.solver_settings import (
    PDLPSolverMode
)

if __name__ == '__main__':
    test_path: str = 'flugpl.mps'

    settings = SolverSettings()
    settings.set_parameter('log_to_console', False)
    settings.set_parameter(CUOPT_PRESOLVE, 0)
    settings.set_parameter(CUOPT_PDLP_SOLVER_MODE, PDLPSolverMode.Stable2)
    settings.set_parameter(CUOPT_ABSOLUTE_DUAL_TOLERANCE, 1e-4)

    problems = []
    for i in range(10):
        problems.append(cuopt_mps_parser.ParseMps(test_path))
    for p in problems:
        for j in range(len(p.variable_types)):
            p.variable_types[j] = CONTINUOUS

    lower_bounds = np.array(problems[0].get_variable_lower_bounds())
    for j in range(10000):
        print(f'Iteration number {j}')
        sol, tim = solver.BatchSolve(problems, settings)
        print(tim)

Expected behavior
No crash

Environment details (please complete the following information):

• Environment location: Ubuntu 24.04 LTS
• Method of cuOpt install: pip3/poetry

[anandhkb]

Trace I am seeing:

(cuopt_env) aanandh@viking-prod-206:~/ncuopt$ python repro_944.py
Iteration number 0
1.958
Iteration number 1
0.227
Iteration number 2
0.189
Iteration number 3
0.178
Iteration number 4
0.205
Iteration number 5
0.253
Iteration number 6
0.26
Iteration number 7
0.185
Iteration number 8
0.187
Iteration number 9
0.251
Iteration number 10
0.906
Iteration number 11
0.304
Iteration number 12
0.212
Iteration number 13
0.254
Iteration number 14
0.199
Iteration number 15
0.201
Iteration number 16
0.184
Iteration number 17
0.186
Iteration number 18
0.181
Iteration number 19
0.283
Iteration number 20
0.897
Iteration number 21
0.328
Iteration number 22
0.199
Iteration number 23
0.218
Iteration number 24
0.204
Iteration number 25
0.199
Iteration number 26
0.181
Iteration number 27
0.183
Iteration number 28
0.204
Iteration number 29
0.196
Iteration number 30
0.428
Iteration number 31
0.666
Iteration number 32
0.317
Iteration number 33
0.209
Iteration number 34
0.197
Iteration number 35
0.182
Iteration number 36
0.186
Iteration number 37
0.216
Iteration number 38
0.19
Iteration number 39
0.222
Iteration number 40
0.646
Iteration number 41
0.589
Iteration number 42
0.228
Iteration number 43
0.189
Iteration number 44
0.196
Iteration number 45
0.207
Iteration number 46
0.204
Iteration number 47
0.185
Iteration number 48
0.193
Iteration number 49
0.2
Iteration number 50
0.304
Iteration number 51
0.879
Iteration number 52
0.359
Iteration number 53
0.228
Iteration number 54
0.197
Iteration number 55
0.201
Iteration number 56
0.195
Iteration number 57
0.179
Iteration number 58
0.189
Iteration number 59
0.195
Iteration number 60
0.278
Iteration number 61
0.944
Iteration number 62
pure virtual method called
terminate called without an active exception
Aborted (core dumped)
(cuopt_env) aanandh@viking-prod-206:~/ncuopt$ 

[anandhkb]

Observations:
Intermittent – Crash around iteration 62, earlier runs are OK.
Solve times – Most solves ~0.18–0.25 s; some spikes (0.9–1.0 s) at 10, 20, 31, 40, 41, 51, 61.
Crash context – Happens during BatchSolve

[anandhkb]

OMP_NUM_THREADS=1 python repro_944.py - does not help. Still crashes in iteration number 56.

[anandhkb]

@Kh4ster @Bubullzz for viz