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Code Analyzer for VB.NET

There is a newer version: 10.5.0.109200

When using ReaderWriterLock and ReaderWriterLockSlim for managing read and write locks,
you should not release a read lock while holding a write lock and vice versa, otherwise you might have runtime exceptions. The locks should be always
correctly paired so that the shared resource is accessed safely.
This rule raises if:

   you call ReaderWriterLock.AcquireWriterLock or ReaderWriterLock.UpgradeToWriterLock
  and then use ReaderWriterLock.ReleaseReaderLock 
   you call ReaderWriterLockSlim.EnterWriteLock or
  ReaderWriterLockSlim.TryEnterWriteLock and then use ReaderWriterLockSlim.ExitReadLock 
   you call ReaderWriterLock.AcquireReaderLock or ReaderWriterLock.DowngradeFromWriterLock and then use ReaderWriterLock.ReleaseWriterLock 
   or you call ReaderWriterLockSlim.EnterReadLock, ReaderWriterLockSlim.TryEnterReadLock, ReaderWriterLockSlim.EnterUpgradeableReadLock or ReaderWriterLockSlim.TryEnterUpgradeableReadLock and then use ReaderWriterLockSlim.ExitWriteLock 

Why is this an issue?
If you use the ReaderWriterLockSlim class, you will get a LockRecursionException. In the case of
ReaderWriterLock, you’ll get a runtime exception for trying to release a lock that is not owned by the calling thread.
Code examples
Noncompliant code example
Public Class Example

    Private Shared rwLock As New ReaderWriterLock()

    Public Sub Writer()
        rwLock.AcquireWriterLock(2000)
        Try
            ' ...
        Finally
            rwLock.ReleaseReaderLock() ' Noncompliant, will throw runtime exception
        End Try
    End Sub

    Public Sub Reader()
        rwLock.AcquireReaderLock(2000)
        Try
            ' ...
        Finally
            rwLock.ReleaseWriterLock() ' Noncompliant, will throw runtime exception
        End Try
    End Sub

End Class

Compliant solution
Public Class Example

    Private Shared rwLock As New ReaderWriterLock()

    Public Shared Sub Writer()
        rwLock.AcquireWriterLock(2000)
        Try
            ' ...
        Finally
            rwLock.ReleaseWriterLock()
        End Try
    End Sub

    Public Shared Sub Reader()
        rwLock.AcquireReaderLock(2000)
        Try
            ' ...
        Finally
            rwLock.ReleaseReaderLock()
        End Try
    End Sub

End Class

Resources
Documentation

   Microsoft Learn - ReaderWriterLock Class 
   Microsoft Learn - ReaderWriterLockSlim