Api 控制器抛出一个与异步相关的异常

Question

我正在构建 Tic-Tac_toe api 游戏。游戏运行正常，直到其中一名玩家按下一个方块以完成游戏（他获胜或填满棋盘）。

当我为最后一步启用所有 CLR 异常时，这是我在行 var user = await UserManager.FindByIdAsync(userId);

中看到的异常

"Additional information: A second operation started on this context before a previous asynchronous operation completed. Use 'await' to ensure that any asynchronous operations have completed before calling another method on this context. Any instance members are not guaranteed to be thread safe."

了解玩家何时单击方块很重要，这是一种 'POST' 方法。 这是我的代码：

public class GamesApiController : ApiController
{
    ApplicationDbContext context = new ApplicationDbContext();

    private ApplicationUserManager _userManager;

    public IEnumerable<ApplicationUser> Get()
    {
        return context.Users;
    }

    public ApplicationUserManager UserManager
    {
        get
        {
            return _userManager ?? System.Web.HttpContext.Current.Request.GetOwinContext().GetUserManager<ApplicationUserManager>();
        }
        private set
        {
            _userManager = value;
        }
    }

    #region Methods
    /// <summary>
    /// update the server data by reciving the model and square and returns the new model
    /// </summary>
    /// <param name="_model"></param>
    /// <param name="squareId"></param>
    /// <returns></returns>

    //square clicked via post
    [Route("api/gamesapi/{squareId}")]
    public async Task<HttpResponseMessage> Post([FromBody]GameModel model, int squareId)
    {
        HttpResponseMessage response;

        if (model == null)
        {
            //Utilites.CreateMsgCookie(Response, "Error", "Sorry, an unknown error has occurred");

            response = Request.CreateErrorResponse(HttpStatusCode.NotFound, "model wasn't found");

            return response;
        }

        //GameModel model = JsonConvert.DeserializeObject<GameModel>(_model);

        Game game = GetGameById(model.Game.GameId);

        if (game == null)
        {
            response = Request.CreateErrorResponse(HttpStatusCode.NotFound, "game wasn't found");
        }
        else
        {
            if (game.UserIdTurn == game.User1Id) //pressing user is user1
            {
                ChangeSquareState(game, squareId, true);
                game.UserIdTurn = game.User2Id;
            }
            else //game.UserIdTurn == game.User2Id - pressing user is user2
            {
                ChangeSquareState(game, squareId, false);
                game.UserIdTurn = game.User1Id;
            }

            SquareState[] board = new SquareState[] {game.Square1,game.Square2,game.Square3,game.Square4,
                                                        game.Square5,game.Square6,game.Square7,game.Square8,game.Square9};

            if (didPlayerWin(board))
            {
                game.WinnerId = model.User.Id;
                await UpdateUserGameState(1, game.User1Id);
                await UpdateUserGameState(2, game.User2Id);
                game.IsGameOver = true;
            }
            else
            {
                bool isBoardFull = true;
                for (int i = 0; i < board.Length; i++)
                {
                    if (board[i] == SquareState.Blank)
                    {
                        isBoardFull = false;
                        break;
                    }
                }
                if (isBoardFull)
                {
                    await UpdateUserGameState(3, game.User1Id);
                    await UpdateUserGameState(3, game.User2Id);
                    game.IsGameOver = true;
                }
            }

            context.SaveChanges();

            response = Request.CreateResponse(HttpStatusCode.OK, game);
        }
        return response;
    }

    /// <summary>
    /// When a game is over, recive a gameState and update the user. 1 for a win, 2 for loss, 3 for aa draw
    /// </summary>
    /// <param name="gameState"></param>
    private async Task UpdateUserGameState(int gameState, string userId)
    {
        var user = await UserManager.FindByIdAsync(userId);
        switch (gameState)
        {
            case 1:

                user.GamesWon++;
                break;

            case 2:
                user.GamesLost++;
                break;

            case 3:
                user.GamesDraw++;
                break;
            default:
                break;

        }
        UserManager.UpdateAsync(user);
    }

    [HttpGet]
    [Route("api/gamesapi/{gameId}")]
    /// <summary>
    /// method to bring the latest game's state from the context and send it back in a GameModel
    /// </summary>
    /// <param name="_model"></param>
    /// <returns></returns>
    public HttpResponseMessage Get(int gameId)
    {
        HttpResponseMessage response;
        Game game = GetGameById(gameId);

        if (game == null)
        {
            response = Request.CreateErrorResponse(HttpStatusCode.NotFound, "game wasn't found");
        }
        else
        {
            response = Request.CreateResponse(HttpStatusCode.OK, game);
        }
        return response;
    }

    /// <summary>
    /// method that check if the board have a line(3 squars in a row)
    /// of the same  element of user1 or user2 , defult - returns fault
    /// </summary>
    /// <param name="board"></param>
    /// <returns></returns>
    private bool didPlayerWin(SquareState[] board)
    {

    }

    /// <summary>
    /// change the SquareState of a specific square of the sent game according to the pressing user
    /// </summary>
    /// <param name="game"></param>
    /// <param name="SquareId"></param>
    /// <param name="_isUser1"></param>

    private void ChangeSquareState(Game game, int SquareId, bool _isUser1)
    {

    }

    /// <summary>
    /// get game from context by gameId , Defult result - null
    /// </summary>
    /// <param name="gameId"></param>
    /// <returns></returns>
    private Game GetGameById(int gameId)
    {

    }
    #endregion
}

Answer 1

我想你错过了在方法 UpdateUserGameState() 中等待 UpdateUserAsync():

private async Task UpdateUserGameState(int gameState, string userId)
{
    var user = await UserManager.FindByIdAsync(userId);

    // ...

    // add missing await
    await UserManager.UpdateAsync(user);
}