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 Function AsyncMethodCaller() As String
Public Class Sample
Public Sub DoSomething()
Dim Example As New AsyncExample()
Dim Caller As New AsyncMethodCaller(Example.SomeMethod)
' Initiate the asynchronous call.
Dim Result As IAsyncResult = Caller.BeginInvoke(Nothing, Nothing) ' Noncompliant: Not paired With EndInvoke
End Sub
End Class
BeginInvoke with callback:
Public Delegate Function AsyncMethodCaller() As String
Public Class Sample
Public Sub DoSomething()
Dim Example As New AsyncExample()
Dim Caller As New AsyncMethodCaller(Example.SomeMethod)
' Initiate the asynchronous call.
Dim Result As IAsyncResult = Caller.BeginInvoke(New AsyncCallback(Sub(ar)
End Sub), Nothing) ' Noncompliant: Not paired With EndInvoke
End Sub
End Class
Compliant solution
BeginInvoke without callback:
Public Delegate Function AsyncMethodCaller() As String
Public Class Sample
Public Function DoSomething() As String
Dim Example As New AsyncExample()
Dim Caller As New AsyncMethodCaller(Example.SomeMethod)
' Initiate the asynchronous call.
Dim Result As IAsyncResult = Caller.BeginInvoke(Nothing, Nothing)
' ...
Return Caller.EndInvoke(Result)
End Function
End Class
BeginInvoke with callback:
Public Delegate Function AsyncMethodCaller() As String
Public Class Sample
Public Sub DoSomething()
Dim Example As New AsyncExample()
Dim Caller As New AsyncMethodCaller(Example.SomeMethod)
' Initiate the asynchronous call.
Dim Result As IAsyncResult = Caller.BeginInvoke(New AsyncCallback(Sub(ar)
' Call EndInvoke to retrieve the results.
Dim Ret As String = Caller.EndInvoke(ar)
' ...
End Sub), Nothing)
End Sub
End Class
Resources
Documentation
