Why is this an issue?

When calling the BeginInvoke method of a delegate, resources are allocated that are only freed up when EndInvoke is called. Failing to pair BeginInvoke with EndInvoke can lead to resource leaks and incomplete asynchronous calls.

This rule raises an issue in the following scenarios:

• The BeginInvoke method is called without any callback, and it is not paired with a call to EndInvoke in the same block.
• A callback with a single parameter of type IAsyncResult does not contain a call to EndInvoke in the same block.

How to fix it

Code examples

Noncompliant code example

BeginInvoke without callback:

public delegate string AsyncMethodCaller();

public static void Main()
{
    AsyncExample asyncExample = new AsyncExample();
    AsyncMethodCaller caller = new AsyncMethodCaller(asyncExample.MyMethod);

    // Initiate the asynchronous call.
    IAsyncResult result = caller.BeginInvoke(null, null); // Noncompliant: not paired with EndInvoke
}

BeginInvoke with callback:

public delegate string AsyncMethodCaller();

public static void Main()
{
    AsyncExample asyncExample = new AsyncExample();
    AsyncMethodCaller caller = new AsyncMethodCaller(asyncExample.MyMethod);

    IAsyncResult result = caller.BeginInvoke(
        new AsyncCallback((IAsyncResult ar) => {}),
        null); // Noncompliant: not paired with EndInvoke
}

Compliant solution

BeginInvoke without callback:

public delegate string AsyncMethodCaller();

public static void Main()
{
    AsyncExample asyncExample = new AsyncExample();
    AsyncMethodCaller caller = new AsyncMethodCaller(asyncExample.MyMethod);

    IAsyncResult result = caller.BeginInvoke(null, null);

    string returnValue = caller.EndInvoke(result);
}

BeginInvoke with callback:

public delegate string AsyncMethodCaller();

public static void Main()
{
    AsyncExample asyncExample = new AsyncExample();
    AsyncMethodCaller caller = new AsyncMethodCaller(asyncExample.MyMethod);

    IAsyncResult result = caller.BeginInvoke(
        new AsyncCallback((IAsyncResult ar) =>
            {
                // Call EndInvoke to retrieve the results.
                string returnValue = caller.EndInvoke(ar);
            }), null);
}

Resources

Documentation

• Calling Synchronous Methods Asynchronously
• Asynchronous Programming Using Delegates
• BeginInvoke()
• EndInvoke()
• AsyncCallback Delegate