为什么 UserManager.GetUserAsync 不返回？

Question

why does UserManager.GetUserAsync not return?

Property IsAdmin will be accessed in blazor UI when i click manually on About page. I don't get why the call to GetUSerAsync does not return. Any clues or mistakes? For simplicity I removed locking code. (doesn't work either without)

About.razor.cs

using System.Collections.Generic;
using System.Linq;
using Common.Server.Logic.Services;
using Common.Shared.Extensions;
using Microsoft.AspNetCore.Components;

namespace Common.Server.UI.Pages
{
    public partial class About : ComponentBase
    {
#nullable disable
        [Inject]
        private UserSessionInfo UserSession { get; set;  }

        private string IsAdminText { get; set; }
        private IEnumerable<string> UserRoleNames { get; set; } = Enumerable.Empty<string>();

#nullable restore

        protected override void OnInitialized()
        {
            IsAdminText = UserSession.IsAdmin.Format();
            UserRoleNames = UserSession.UserRoles;
        }
    }
}

UserSessionInfo.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using AspNetCore.ServiceRegistration.Dynamic.Interfaces;
using Common.Server.Logic.Bases;
using Common.Shared;
using Common.Shared.Extensions;
using Common.Shared.Models.Logging.Bases;
using Microsoft.AspNetCore.Components.Authorization;
using Microsoft.AspNetCore.Identity;

namespace Common.Server.Logic.Services
{
    public class UserSessionInfo : LockingBase, IHasUsername, IScopedService
    {
        public DateTime LoginAt { get; set; }

        private UserManager<IdentityUser> UserManager { get; }
        private AuthenticationStateProvider AuthenticationStateProvider { get; }

        public IEnumerable<string> UserRoles { get; private set; } = Enumerable.Empty<string>();

        private string? _username;
        public string? Username
        {
            get
            {
                CheckInitialized();

                return _username;
            }
        }

        private bool _isAdmin;
        public bool IsAdmin
        {
            get
            {
                CheckInitialized();

                return _isAdmin;
            }
        }

        public UserSessionInfo(IServiceProvider serviceProvider)
        {
            UserManager = serviceProvider.GetRequiredService<UserManager<IdentityUser>>();
            AuthenticationStateProvider = serviceProvider.GetRequiredService<AuthenticationStateProvider>();
        }

        private void CheckInitialized()
        {
            if (_username is null)
                // double lock
                SyncLock.Lock(async () => await InitializeAsync()).GetAwaiter().GetResult();
        }

        private async Task InitializeAsync()
        {
            var claimsPrincipal = (await AuthenticationStateProvider.GetAuthenticationStateAsync()).User;

            var user = await UserManager.GetUserAsync(claimsPrincipal); // Does not return
            _isAdmin = await UserManager.IsInRoleAsync(user, Const.Authorization.Roles.AdminRoleName);

            UserRoles = await UserManager.GetRolesAsync(user);

            var username = await UserManager.GetUserNameAsync(user);
            Interlocked.Exchange(ref _username, username);
        }
    }
}

also (startup.cs):

services.AddDefaultIdentity<IdentityUser>()
                .AddRoles<IdentityRole>()
                .AddClaimsPrincipalFactory<UserClaimsPrincipalFactory<IdentityUser, IdentityRole>>()
                .AddEntityFrameworkStores<ApplicationDbContext>()
                .AddDefaultTokenProviders()
                .AddDefaultUI();

services.AddScoped<AuthenticationStateProvider, RevalidatingIdentityAuthenticationStateProvider<IdentityUser>>();

services.AddScoped<UserSessionInfo>();

Answer 1

When an async method doesn't return then .GetAwaiter().GetResult() is the first suspect.

Most likely your calling code (the renderer?) is getting your Username and IsAdmin properties overlapped, and then you have a deadlock. But we can't be sure without seeing the whole call chain.

As a rule of thumb, you shouldn't need locking or GetResult (or.Wait(), .Result). When you think you do it may be time to back up.

Answer 2

Finally I found the solution. (and the reason why it din't work)

The problem was that I accessed IsAdmin during OnInitialized callback instead of OnInitializedAsync.

Putting access to IsAdmin into OnInitializedAsync everything works!