Question

abstract class Foo {     private List<Object> container;     private bool update;      Foo Foo()     {         container = new List<object>();         update = false;     }      public abstract Bar CreateBar();      public void BeginUpdate()     {         if (!update)         {             Thread update_thread = new Thread(new ThreadStart(Update));             update_thread.Start();         }     }      private void Update()     {         update = true;         while (update)         {             lock (container)             {                 if (...)                     container.Add(this.CreateBar());                 else                     container.Remove(...);             }              Thread.Sleep(1337);         }     }      public void EndUpdate()     {         update = false;     }      public List<Object> Objects     {         get         {             lock (container)             {                 return this.container;             }         }     } } 

When something outside of Foo calls the Foo’s Object accessor like,

List<Objects> objects = foo_instance.Objects; foreach (Object o in objects) {     Thread.Sleep(31173); } 

How will the locking occur? Will the thread running Update() have to wait until the above foreach is done processing objects list? I would like that these two would work simultaneously, is the only solution to make a deep copy of objects?

Answer 1

Your code does not do what you think it does. This method

public List<Object> Objects {     get     {         lock (container)         {             return this.container;         }     } } 

Does not hold the lock after it has returned the value. So your loop is not locked.

You cannot return the container instance from the clas