I’m learning java and wrote a recursive function search to find the best move in a simple board game for one player using brute force.

class Game {
    class Move{
        int x, y, value;
        //constructors
    };
    class Board{}; //and all necessary functions

    private Move search(Board board) {
        if (gameOver(board)) {
            return new Move(evaluateBoard(board));
        }
        var bestMove = new Move();
        for (var move : getMoves(board)) {
            move.value = search(makeMove(board, move)).value;
            if (move.value > bestMove.value) {
                bestMove = move;
            }
        }
        return bestMove;
    }
}

Now I’m trying to make multi-threaded searchParallel. I can’t use the fork and join framework because I can’t split the function into independent parts. I tried the following but it doesn’t work

    AtomicInteger threadCount = new AtomicInteger();
    private static final int MAX_THREADS = 10;
    ExecutorService executorService = Executors.newFixedThreadPool(MAX_THREADS);

    private Move searchParallel(Board board) throws InterruptedException, ExecutionException {
        if (gameOver(board)) {
            return new Move(evaluateBoard(board));
        }
        List<Callable<Move>> tasks = new ArrayList<>();
        var lock = new Object();
        var bestMove = new Move();
        for (var move : getMoves(board)) {
            if(threadCount.get() < MAX_THREADS){
                threadCount.incrementAndGet();
                tasks.add(() -> {
                    var bestMove1 = new Move();
                    move.value = searchParallel(makeMove(board, move)).value;
                    synchronized (lock){
                        if (move.value > bestMove1.value) {
                            bestMove1 = move;
                        }
                    }
                    threadCount.decrementAndGet();
                    return bestMove1;
                });
            }
            else {
                move.value = searchParallel(makeMove(board, move)).value;
                synchronized (lock) {
                    if (move.value > bestMove.value) {
                        bestMove = move;
                    }
                }
            }
        }
        var results = executorService.invokeAll(tasks);
        for(var move : results){
            if (move.get().value > bestMove.value) {
                bestMove = move.get();
            }
        }
        return bestMove;
    }