IMobileServiceClient.PullAsync 尝试与 Azure 移动服务同步时出现死锁

Question

我有下面的 classes。

public class AzureMobileDataContext : IAsyncInitialization
    {
        private static readonly Lazy<AzureMobileDataContext> lazy =
            new Lazy<AzureMobileDataContext> (() => 
                new AzureMobileDataContext(
                    new MobileServiceClient(
                                "http://myservice.azure-mobile.net/",
                                "123456789ABCDEFGHIJKLMNOP")));

        public static AzureMobileDataContext Instance { get { return lazy.Value; } }
        public Task Initialization { get; private set; }
        public IMobileServiceClient Context { get; private set; }

        private Object lockObj = new Object ();
        private static MobileServiceSQLiteStore store;

        public AzureMobileDataContext (IMobileServiceClient context)
        {
            Context = context;
            Initialization = Init ();
            Initialization.ContinueWith (async (antecedent) => {
                await Context.SyncContext.InitializeAsync (store, new MobileServiceSyncHandler ());
            });
        }

        private Task Init ()
        {
            return Task.Run (() => {
                lock (lockObj) {
                    if (!Context.SyncContext.IsInitialized) {
                        try {
                            store = new MobileServiceSQLiteStore ("mysqlite.db3");

                            store.DefineTable<Post> ();
                            store.DefineTable<PostPhotoUrl> ();
                            store.DefineTable<User> ();
                            store.DefineTable<Club> ();
                            store.DefineTable<District> ();
                        } catch (Exception ex) {
                            Debug.WriteLine ("Init: {0}", ex.Message);
                        }
                    }
                }
            });
        }

        public async Task<IMobileServiceSyncTable<TEntity>> GetTableAsync<TEntity> ()
        {
            await Initialization;
            return Context.GetSyncTable<TEntity> ();
        }

        public async Task PushAsync ()
        {
            try {
                await Initialization;
                await Context.SyncContext.PushAsync ();
            } catch (MobileServiceInvalidOperationException invalidOperationEx) {
                Debug.WriteLine (invalidOperationEx.Message);
            } catch (MobileServicePushFailedException pushFailedException) {
                Debug.WriteLine (pushFailedException.Message);
            }
        }

        public async Task PullAsync<TEntity> (IMobileServiceTableQuery<TEntity> query)
        {
            try {
                await Initialization;
                IMobileServiceSyncTable<TEntity> entityTable = await GetTableAsync<TEntity> ();
                await entityTable.PullAsync (typeof(TEntity).ToString (), query); // Never returns, no exception is caught or thrown.
                await entityTable.PurgeAsync ();
            } catch (MobileServiceInvalidOperationException preconditionFailedEx) {
                Debug.WriteLine (preconditionFailedEx.Message);
            } catch (Exception ex) {
                Debug.WriteLine (ex.Message);
            }
        }

        public async Task SyncAsync<TEntity> ()
        {
            await PushAsync ();
            IMobileServiceSyncTable<TEntity> syncTable = await GetTableAsync<TEntity> ();
            await PullAsync (syncTable.CreateQuery ());
        }
    }

我使用我拥有的 BaseRepository 中的这个单例，它是 5 个不同实体存储库的基础 class。

public abstract class BaseRepository<TEntity> : IRepository<TEntity> where TEntity : class
    {
        protected AzureMobileDataContext MobileServiceContext { get { return AzureMobileDataContext.Instance; } }

        protected virtual Task PushAsync ()
        {
            return MobileServiceContext.PushAsync ();
        }

        protected virtual Task PullAsync (IMobileServiceTableQuery<TEntity> query)
        {
            return MobileServiceContext.PullAsync (query);
        }

        public virtual async Task<DataObjectResponse<IEnumerable<TEntity>>> FindAsync (Expression<Func<TEntity, bool>> predicate)
        {
            IMobileServiceSyncTable<TEntity> syncTable = await MobileServiceContext.GetTableAsync<TEntity> ();
            await PullAsync (syncTable.CreateQuery ());
            IEnumerable<TEntity> entities = await syncTable.Where (predicate).ToEnumerableAsync ();
            return new DataObjectResponse<IEnumerable<TEntity>> (entities);
        }
}

用户存储库。

public class UsersAzureRepository : BaseRepository<User>, IUsersRepository
    {
        public UsersAzureRepository ()
        {
        }

        public async Task<DataObjectResponse<User>> FindByIdAsync (string entityId)
        {
            DataObjectResponse<IEnumerable<User>> users = await FindAsync (p => p.Id == entityId);
            return new DataObjectResponse<User>(users.Data.FirstOrDefault ());
        }
    }

包含 GetUserById 方法的 DataService Facade class。

public async Task<UserModel> GetUserById (string userId)
        {
            DataObjectResponse<User> users = await UsersRepository.FindByIdAsync (userId);
            UserModel userModel = Mapper.Map<User, UserModel> (users.Data);
            return userModel;
        }

用户查看模型方法。

public async Task<UserModel> GetUsersAsync() // testing purposes
        {
            UserModel user = await _dataService.GetUserById("032beb3b-1cbf-4a0d-809c-a25c71139c55"); 
            if (user != null) {
                Debug.WriteLine ("User loaded: {0}", user.Id);
            }
            return user;
        }

从 iOS UIViewController 调用。

public async override void ViewDidLoad ()
        {
            base.ViewDidLoad ();

            UserModel user = await ViewModel.GetUsersAsync ();
        }

AzureMobileDataContext 更像是 IMobileServiceClient 上下文操作的线程安全包装器，确保不会有多个线程尝试初始化数据库（我在直接使用它时出现异常BaseRepository<T>之前）。

从这里我不太确定问题出在哪里。我怀疑包装器不是最佳解决方案，欢迎提出任何建议。

还有其他调试 PullAsync 方法的方法吗？

[编辑]

本地 SQLite 数据库从远程服务同步 table 数据，但仍然没有调用 return。

Answer 1

问题出在服务器端的 Azure 移动服务中。

我从 TableController returning 一个 IEnumerable 但 SDK 使用 OData 查询表达式来完成它自己的工作，returning 一个 IEnumerable 是不够的，更改为 IQueryable 解决了这个问题拉取数据时不断循环。

我坚信服务器 return 类型不应该与 SDK 相关，但这就是它的工作方式。

IMobileServiceClient.PullAsync 尝试与 Azure 移动服务同步时出现死锁

IMobileServiceClient.PullAsync deadlock when trying to sync with Azure Mobile Services

deadlock

ios

async-await

xamarin

azure-mobile-services