LazySingleton.cs

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using System;
using System.Threading;
 
namespace Csla
{
  public sealed class LazySingleton<T> : Core.IUseApplicationContext
    where T : class
  {
    private readonly object _syncRoot = new object();
    private T _value;
    private readonly Func<T> _delegate;
    private bool _isValueCreated;
 
    ApplicationContext Core.IUseApplicationContext.ApplicationContext { get => ApplicationContext; set => ApplicationContext = value; }
    private ApplicationContext ApplicationContext { get; set; }
 
    public LazySingleton()
    {
      _delegate = () => (T)ApplicationContext.CreateInstanceDI(typeof(T));
    }
 
    public LazySingleton(Func<T> @delegate)
    {
      _delegate = @delegate;
    }
 
    public bool IsValueCreated
    {
      get { return _isValueCreated; }
    }
 
    public T Value
    {
      get
      {
        if (!_isValueCreated) // not initialized 
        {
          lock (_syncRoot)       // lock syncobject
          {
            if (!_isValueCreated) // recheck for initialized after lock is taken
            {
               _value = _delegate.Invoke();
              _isValueCreated = true;   // mark as initialized
            }
          }
        }
 
        return _value;
      }
    }
  }
}