CpSolver.StopSearch() Dead Lock

[flyish]

What version of OR-Tools and what language are you using?
Version: 9.14.6206
Language: C#

Which solver are you using (e.g. CP-SAT, Routing Solver, GLOP, BOP, Gurobi)
CP-SAT

What operating system (Linux, Windows, ...) and version?
Windows

What did you do?
Steps to reproduce the behavior:

1. Create solver: var solver = new CpSolver();
2. Slove Model: var status = solver.Solve(model, cb);
3. Call solver.StopSearch() by another thread
4. dead lock: StopSearch() do not return, SolveWrapper.Dispose() wait StopSearch() Thread free lock

What did you expect to see

What did you see instead?

Make sure you include information that can help us debug (full error message, model Proto).

Anything else we should know about your project / environment