Raise an event when all asynchronous method calls are completed

Question

I have the following problem: In an asynchronous context, I need to initialize the fields of some user object before I can continue with other operations on it, so I do:

class ContainingObject
{    
   private CustomObject _co;

   SomeMethod()
   {
     _co = new CustomObject();
     _co.InitObjectAsyncCompleted += (s,e) => DoStuff();
     _co.InitObjectAsync();
   }    
}

class CustomObject
{
   public string Field1, Field2, Field3, Field4;

   public EventHandler InitObjectAsyncCompleted;

   public void InitObjectAsync()
   {
   }    
}

The trick is that the fields are also initialized via asynchronous calls to the WCF service, and they must all be initialized before I raise the InitObjectAsyncCompleted event. There are quite a few such fields, each of which is initialized using another WCF call, and implying that I cannot change part of WCF at the moment, I see two ways to solve the problem:

1) Chain WCF , , WCF .., , "" WCF.

public void InitObjectAsync()
{  
    var proxy = new ProxyFactory.GetCustomObjectProxy;
    proxy.GetDataForField1Completed += (s,e) => 
    { 
        Field1 = e.Result;
        proxy.GetDataForField2Completed += (s1,e1) => 
        { 
          Field2 = e1.Result; 
          //keep this up building a chain of events, when Field4 is filled, raise
          // InitObjectAsyncCompleted(this, null);          
        };
        proxy.GetDataForField2();
    };
    proxy.GetDataForField1();
} 

2) , , 4 .

public void InitObjectAsync()
{  
    int counter = 0;
    var proxy = new ProxyFactory.GetCustomObjectProxy;
    proxy.GetDataForField1Completed += (s,e) => 
    { 
        Field1 = e.Result;
        if(counter >= 3)
            InitObjectAsyncCompleted(this, null);
        else
            counter++;
    };
    proxy.GetDataForField1();
    proxy.GetDataForField2Completed += (s,e) => 
    { 
        Field2 = e.Result;
        if(counter >= 3)
            InitObjectAsyncCompleted(this, null);
        else
            counter++;
    };
    proxy.GetDataForField2();
    //repeat for all fields
}

, , - ... - - ?

Answer 1

, , .

, , , . , :

private int _outstandingRequests = 0;

public void InitObjectAsync()
{
    RequestField( proxy.GetDataForField1,
                  proxy.GetDataForField1Completed, 
                  s => Field1 = s );

    RequestField( proxy.GetDataForField2, 
                  proxy.GetDataForField2Completed,
                  s => Field2 = s );

    RequestField( proxy.GetDataForField3, 
                  proxy.GetDataForField3Completed,
                  s => Field3 = s );
    // ... and so on...
}

// This method accepts two actions and a event handler reference.
// It composes a lambda to perform the async field assignment and internally
// manages the count of outstanding requests. When the count drops to zero,
// all async requests are finished, and it raises the completed event.

private void RequestField<T>( Action fieldInitAction, 
                              EventHandler fieldInitCompleteEvent,
                              Action<T> fieldSetter )
{
    // maintain the outstanding request count...
    _outstandingRequests += 1;

    // setup event handler that responds to the field initialize complete        
    fieldInitCompleteEvent += (s,e) =>
    {
        fieldSetter( e.Result );

        _outstandingRequests -= 1;

        // when all outstanding requests finish, raise the completed event
        if( _outstandingRequests == 0 )
           RaiseInitCompleted();
    }

    // call the method that asynchronously retrieves the field value...
    fieldInitAction();
}

private void RaiseInitCompleted()
{
    var initCompleted = InitObjectAsyncCompleted;
    if( initCompleted != null )
        initCompleted(this, null);
}

Answer 2

Parallel extensions .NET 4.0, :

Task[] tasks = new Task[3]
{
    Task.Factory.StartNew(() => MethodA()),
    Task.Factory.StartNew(() => MethodB()),
    Task.Factory.StartNew(() => MethodC())
};

//Block until all tasks complete.
Task.WaitAll(tasks);

Answer 3

WCF -. ( , ), , . .

Monitor.Enter. WCF . . , , , . , init . . , ( waitingRoom, , ).

, WCF, , , , WCF, -.