Quick POSTs to DisplayPreferences endpoint can lead to database concurrency problems

[ferferga]

Describe the bug When posting to https://api.jellyfin.org/#operation/UpdateDisplayPreferences too quickly, the server's controller might run the same database query at the same time, leading to concurrency problems

System (please complete the following information):

• OS: Debian
• Virtualization: Docker
• Clients: Vue
• Jellyfin Version: RC3
• System: Raspberry Pi 4

To Reproduce

1. Login using jellyfin-vue
2. Change between darkMode and light mode really quick (multiple times in less than a second)
3. Error will appear and the following log will be printed:

[2021-02-17 22:37:16.615 +00:00] [ERR] [101] Jellyfin.Server.Middleware.ExceptionMiddleware: Error processing request. URL "GET" "/DisplayPreferences/usersettings".
Microsoft.EntityFrameworkCore.DbUpdateException: An error occurred while updating the entries. See the inner exception for details.
 ---> Microsoft.Data.Sqlite.SqliteException (0x80004005): SQLite Error 19: 'UNIQUE constraint failed: CustomItemDisplayPreferences.UserId, CustomItemDisplayPreferences.ItemId, CustomItemDisplayPreferences.Client, CustomItemDisplayPreferences.Key'.
   at Microsoft.Data.Sqlite.SqliteException.ThrowExceptionForRC(Int32 rc, sqlite3 db)

Also this appears afterwards:

[2021-02-17 22:37:16.668 +00:00] [ERR] [147] Jellyfin.Server.Middleware.ExceptionMiddleware: Error processing request. URL "POST" "/DisplayPreferences/usersettings".
System.InvalidOperationException: A second operation was started on this context before a previous operation completed. This is usually caused by different threads concurrently using the same instance of DbContext. For more information on how to avoid threading issues with DbContext, see https://go.microsoft.com/fwlink/?linkid=2097913.
   at Microsoft.EntityFrameworkCore.Internal.ConcurrencyDetector.EnterCriticalSection()
   at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.Enumerator.MoveNext()
   at System.Linq.Enumerable.SingleOrDefault[TSource](IEnumerable`1 source)
   at lambda_method537(Closure , QueryContext )
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.Execute[TResult](Expression expression)
   at System.Linq.Queryable.FirstOrDefault[TSource](IQueryable`1 source, Expression`1 predicate)
   at Jellyfin.Server.Implementations.Users.DisplayPreferencesManager.GetDisplayPreferences(Guid userId, Guid itemId, String client)
   at Jellyfin.Api.Controllers.DisplayPreferencesController.UpdateDisplayPreferences(String displayPreferencesId, Guid userId, String client, DisplayPreferencesDto displayPreferences)
   at lambda_method755(Closure , Object , Object[] )
   at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.SyncActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeActionMethodAsync()
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeNextActionFilterAsync()

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[nielsvanvelzen]

Running into this issue in jellyfin-androidtv with 10.7.7 after our move to the SDK for loading display preferences (which makes simultaneous requests to retrieve multiple display preferences). We're just GETting instead of POSTing though.

[2021-10-19 19:37:16.231 +02:00] [ERR] [19] Jellyfin.Server.Middleware.ExceptionMiddleware: Error processing request. URL "GET" "/DisplayPreferences/usersettings".
System.InvalidOperationException: A second operation was started on this context before a previous operation completed. This is usually caused by different threads concurrently using the same instance of DbContext. For more information on how to avoid threading issues with DbContext, see https://go.microsoft.com/fwlink/?linkid=2097913.
   at Microsoft.EntityFrameworkCore.Internal.ConcurrencyDetector.EnterCriticalSection()
   at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.Enumerator.MoveNext()
   at System.Linq.Enumerable.SingleOrDefault[TSource](IEnumerable`1 source)
   at Jellyfin.Server.Implementations.Users.DisplayPreferencesManager.GetDisplayPreferences(Guid userId, Guid itemId, String client)
   at Jellyfin.Api.Controllers.DisplayPreferencesController.GetDisplayPreferences(String displayPreferencesId, Guid userId, String client)
   at lambda_method321(Closure , Object , Object[] )
   at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.SyncObjectResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeActionMethodAsync()
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeNextActionFilterAsync()

[barronpm]

It looks like two different issues are being described here: The first being this stacktrace:

[2021-02-17 22:37:16.615 +00:00] [ERR] [101] Jellyfin.Server.Middleware.ExceptionMiddleware: Error processing request. URL >"GET" "/DisplayPreferences/usersettings".
Microsoft.EntityFrameworkCore.DbUpdateException: An error occurred while updating the entries. See the inner exception for >details.
---> Microsoft.Data.Sqlite.SqliteException (0x80004005): SQLite Error 19: 'UNIQUE constraint failed: >CustomItemDisplayPreferences.UserId, CustomItemDisplayPreferences.ItemId, CustomItemDisplayPreferences.Client, >CustomItemDisplayPreferences.Key'.
  at Microsoft.Data.Sqlite.SqliteException.ThrowExceptionForRC(Int32 rc, sqlite3 db)

which seems to be caused by trying to concurrently update the same entry, the fix for which is non-trivial without extensive locking at first glance.

The second is a problem with multiple requests to the same context being invoked simultaneously due to some weird behavior, potentially in our middleware? I'll have to investigate this further.