In my Asp.Net MVC projects, I use NInject providers to create instances of UnitOfWork. (I use Mindscape.LightSpeed)
Here is a sample of binding in my NinjectModule class:
base.Bind<IUnitOfWork>().ToProvider(UnitOfWorkProvider<UnitOfWork>.CreateInstance(_lightSpeedContext, UnitOfWorkProvider.CreateUnitOfWork)).InRequestScope();
And here is an example of what I'm doing in the provider to create instances:
protected override T CreateInstance(IContext context)
{
T unitOfWork = default(T);
unitOfWork = this.CreateUnitOfWork();
if (this.ConnectionStrategy != null)
unitOfWork.ConnectionStrategy = this.ConnectionStrategy;
return unitOfWork;
}
Should it be better to use mutex object like the example below?
private static readonly Mutex _mutex = new Mutex();
protected override T CreateInstance(IContext context)
{
_mutex.WaitOne();
try
{
T unitOfWork = default(T);
unitOfWork = this.CreateUnitOfWork();
if (this.ConnectionStrategy != null)
unitOfWork.ConnectionStrategy = this.ConnectionStrategy;
return unitOfWork;
}
finally
{
_mutex.ReleaseMutex();
}
}
I don't found any example of using mutex with Ninject provider on the Net and this is why I ask the question.
It would be nice to have an explanation of why mutex is or not good in the context of Asp.Net MVC.
Thank you very much.
Why do you want to use mutex, when you are declaring your IUnitOfWork in request scope?
It would be bottle-neck for your web application, because parallel requests will be waiting for another to create an instance of IUnitOfWork. Widely used practice is to create one instance of unit of work or database context (connection) etc. per web request (IDisposable objects will be disposed at the end of the request). Even if you declare your component InSingletonScope, Ninject should take care of concurrency issues.
Related
The application was developed on ASP NET Core 3. To log user actions, I decided to use a single method in the Project class. Faced the problem of using one singleton dbContext from different threads.
Startup.cs
public void ConfigureServices(IServiceCollection services)
{
string connection = Configuration.GetConnectionString("ConnectionDB");
services.AddDbContext<DataBaseContext>(options => options.UseSqlServer(connection), ServiceLifetime.Transient, ServiceLifetime.Singleton);
services.AddSingleton<Project>();
}
Project.cs
public async Task AddUserLog(string action, string message, int userId)
{
try
{
UserLog userLog = new UserLog()
{
Action = action,
Message = message,
UserId = userId
Datepoint = DateTime.Now
};
_dbContext.UserLog.Add(userLog);
await _dbContext.SaveChangesAsync();
}
catch (Exception ex)
{
await AddSystemLog("Project", "AddUserLog", ex.Message);
}
}
SchemeController.cs
public class SchemeController : ControllerBase
{
private readonly Project _project;
public SchemeController(Project project)
{
_project = project;
}
[Authorize(Policy = "AdvancedControl")]
[HttpPost("[action]")]
public async Task SomeMethode()
{
for (int i = 0; i < 10; i++)
{
await _project.AddUserLog("Text", "Message", 42);
}
}
}
Already at the second iteration of the loop, I catch an exception in the AddUserLog method:
"A second operation started on this context before a previous operation completed. This is usually caused by different threads using the same instance of DbContext."
I suggest several solutions:
Add the log to the buffer table and then save it to the database by timer. But this is not the best way out;
Block the method while it is being saved to the database.
But I don’t like any of the options.
Please tell me the correct approach in solving this issue.
So, you trying to use shared resource (singleton Project class) to perform parallel operations (save UserLogs) while your shared resource implementation is not thread-safe (exceptions raised).
You have at lease three ways to solve this:
Do not use shared resource: register Project per scope instead of singletone;
Do not perform operations in parallel: seems hard to achieve because you making webapp and you can't force user(s) to wait
Refactor your resource to be thread-safe: add locks/mutexes/buffering... inside Project
There is no one "correct" way - all 3 are correct. Choose one you like (or combine several).
Usually using scoped dbcontext is recommended (because connections are pooled), but it's the creator of app who should decide.
Having an huge customers profile page if two or more users start using same page and start editing big change will happen in my database so planing to implement Threads concept where only one user can use that customer page
i'm aware about threads concept but confused how to implement it
hope i need to use Singleton class as well
Any suggestion or Logic's will be helpful
I'm using Struts,Hibernate frame work
You may use application context to store a flag variable. Action will use its value to allow only one simultaneous execution.
public class TestAction extends ActionSupport implements ApplicationAware {
private static final String APP_BUSY_KEY = "APP_BUSY";
Map<String, Object> map;
#Override
public void setApplication(Map<String, Object> map) {
this.map = map;
}
#Override
public String execute() throws Exception {
if (map.containsKey(APP_BUSY_KEY)) {
return ERROR;
} else {
map.put(APP_BUSY_KEY, "1");
try {
// action logic here
} finally {
map.remove(APP_BUSY_KEY);
}
return SUCCESS;
}
}
}
If you plan to implement similar logic for two requests (lock after displaying values and release lock after submitting new values) then logic will be more complex and you will also need to handle lock release after timeout.
I've seen so many questions similar to mine, but no answers that quite seem to apply to my situation.
My ASP.NET MVC app with EF 6 Code first and Unity has a web service that adds something to the database, then fires off another thread that adds more stuff to the database. The reason for using the other thread is to return the original request as quickly as possible. The context class is obtained using the Unity container RegisterType().
I've got lots of repository classes all using the same context, so to make sure they get the same instance I could use the PerRequestLifetimeManager in my Unity container, and that's fine for the http request threads but that the other threads can't use the context returned by the PerRequestLifetimeManager because this is only valid on the original http request thread.
So, I can use the PerThreadLifetimeManager. This is great because now the main request thread and the other thread it kicks off get the same instance of the context returned by Unity. The trouble is that so do other requests if they get given the same thread, so this is no good either.
So how can I configure things so that the request threads get their own PerRequest Lifetime Manager created context, and other threads get a different context?
The issue is made a little more difficult by the fact that the new thread calls other classes that need to use a context instance. However, these other classes can be used from the main request thread or the new thread, so grabbing a context instance when the thread is started and then passing it around will be tricky.
Thanks in advance
No takers then...
I'm going to have a go at answering my own question, but could do with some thoughts on my approach.
So I can't use the PerRequestLifetimeManager because worker threads can't use the context that this returns, but I can't use the PerThreadLifetimeManager because the context can last the lifetime of several HTTP requests. This class attempts to provide the best of both worlds.
/// <summary>
/// For the context class the PerRequestLifetimeManager is the most suitable lifetime manager,
/// but this doesn't work when a new worker thread is started as this needs to access the context.
/// The PerThreadLifetimeManager is no good either as the context can last for more than on request.
/// This class attempts to give the best of both worlds: per request lifetime management for HTTP requests
/// and thread storage for worker threads.
/// </summary>
public class PerRequestOrThreadLifetimeManager : PerRequestLifetimeManager, IDisposable
{
private const string threadDataSlotName = "PerRequestOrThreadLifetimeManager";
public override object GetValue()
{
if (System.Web.HttpContext.Current != null)
{
return base.GetValue();
}
else
{
return getManagedObject();
}
}
public override void RemoveValue()
{
throw new NotImplementedException();
}
public override void SetValue(object newValue)
{
if (System.Web.HttpContext.Current != null)
{
base.SetValue(newValue);
}
else
{
Thread.SetData(Thread.GetNamedDataSlot(threadDataSlotName), newValue);
}
}
private object getManagedObject()
{
return Thread.GetData(Thread.GetNamedDataSlot(threadDataSlotName));
}
public void Dispose()
{
try
{
IDisposable obj = getManagedObject() as IDisposable;
if (obj != null)
{
obj.Dispose();
obj = null;
}
}
catch { }
}
}
In an MVC / WebAPI environment I would use InRequestScope to bind the DbContext.
However, I am now on a Console application / Windows service / Azure worker role (doesn't really matter, just there's no Web request scope), which periodically creates a number of Tasks that run asynchronously. I would like each task to have its own DbContext, and since tasks run on their own thread, I tried binding DbContext using InThreadScope.
Unfortunately, I realize that the DbContext is not disposed when a task is finished. What actually happens is, the thread returns to the Thread Pool and when it is assigned a new task, it already has a DbContext, so DbContexts stay alive forever.
Is there a way InThreadScope can be used here or should I use some other scope? How can ThreadScope be used when threads are returning from ThreadPool every now and then?
If you decide to go on with custom scope, the solution is:
public sealed class CurrentScope : INotifyWhenDisposed
{
[ThreadStatic]
private static CurrentScope currentScope;
private CurrentScope()
{
}
public static CurrentScope Instance => currentScope ?? (currentScope = new CurrentScope());
public bool IsDisposed { get; private set; }
public event EventHandler Disposed;
public void Dispose()
{
this.IsDisposed = true;
currentScope = null;
if (this.Disposed != null)
{
this.Disposed(this, EventArgs.Empty);
}
}
}
Binding:
Bind<DbContext>().To<MyDbContext>().InScope(c => CurrentScope.Instance)
And finally:
using (CurrentScope.Instance)
{
// your request...
// you'll get always the same DbContext inside of this using block
// DbContext will be disposed after going out of scope of this using block
}
Using asp.net identity RTW version.
I need to perform several actions in a transaction, including both UserMananger function calls and other operations on my DbContext (example: create new user, add it to group and perform some business-logic operations).
How should I do this?
My thoughts follow.
TransactionScope
using (var scope = new TransactionScope(TransactionScopeOption.Required))
{
// Do what I need
if (everythingIsOk) scope.Complete();
}
The problem is: UserManager functions are all async, and TransactionScope was not designed to work with async/await. It seems to be solved in .Net Framework 4.5.1. But I use Azure Web Sites to host my project builds, so I cannot target 4.5.1 yet.
Database transaction
public class SomeController : Controller
{
private MyDbContext DbContext { get; set; }
private UserManager<User> UserManager { get; set; }
public AccountController()
{
DbContext = new MyDbContext()
var userStore = new UserStore<IdentityUser>(DbContext);
UserManager = new UserManager<IdentityUser>(userStore);
}
public async ActionResult SomeAction()
{
// UserManager uses the same db context, so they can share db transaction
using (var tran = DbContext.Database.BeginTransaction())
{
try
{
// Do what I need
if (everythingIsOk)
tran.Commit();
else
{
tran.Rollback();
}
}
catch (Exception)
{
tran.Rollback();
}
}
}
}
That seems to work, but how can I unit-test it?
UserManager<> constructor accepts IUserStore<>, so I can easily stub it.
UserStore<> constructor accepts DbContext, no idea how I can stub this.
You can implement your own test user store that can be stubbed out for your unit test.
If you want to use the actual EF UserStore in your tests, that also will work, but it will be creating a database using the DefaultConnection string by default. You could specify a DatabaseInitializer to always drop/recreate your tables in your tests if you wanted to ensure a clean db for every test.