Why is this an issue?

To prevent potential deadlocks in an application, it is crucial to release any locks that are acquired within a method along all possible execution paths.

Failing to release locks properly can lead to potential deadlocks, where the lock might not be released, causing issues in the application.

This rule specifically focuses on tracking the following types from the System.Threading namespace:

An issue is reported when a lock is acquired within a method but not released on all paths.

Exceptions

If the lock is never released within the method, no issue is raised, assuming that the callers will handle the release.

How to fix it

To make sure that a lock is always released correctly, you can follow one of these two methods:

Use a SyncLock statement with your lock object.
Use a Try-Finally statement and put the release of your lock object within a Finally block.

Code examples

Noncompliant code example

Class Example
    Private obj As Object = New Object()

    Public Sub DoSomethingWithMonitor()
        Monitor.Enter(obj) ' Noncompliant: not all paths release the lock

        If IsInitialized() Then
            ' ...
            Monitor.Exit(obj)
        End If
    End Sub
End Class

Class Example
    Private lockObj As ReaderWriterLockSlim = New ReaderWriterLockSlim()

    Public Sub DoSomethingWithReaderWriteLockSlim()
        lockObj.EnterReadLock() ' Noncompliant: not all paths release the lock
        If IsInitialized() Then
            ' ...
            lockObj.ExitReadLock()
        End If
    End Sub
End Class

Compliant solution

Class Example
    Private obj As Object = New Object()

    Public Sub DoSomethingWithMonitor()
        SyncLock obj ' Compliant: the lock will be released at the end of the SyncLock block
            If IsInitialized() Then
                ' ...
            End If
        End SyncLock
    End Sub
End Class