CODEWITHSUNDEEP
vb.netmultithreadingtestingsynchronizationsynclock
Mike Perrenoud
Mike Perrenoud

Reputation: 67898

SyncLock not working in unit tests

I've got a Module that I'm wanting to use to cache some stuff. It's pretty simple. I wanted to shy away from the ConcurrentDictionary because it needs to be a guaranteed operation.

Public Module SchemaTableCache
    Private lockObject As New Object
    Private columnCache As New Dictionary(Of String, SortedSet(Of String))

    <Extension>
    Public Sub CacheSchemaTable(dataReader As IDataReader, name As String)
        SyncLock lockObject
            Dim rows As New List(Of DataRow)
            If columnCache.ContainsKey(name) Then
                Return
            End If

            rows = dataReader.GetSchemaTable().Rows.OfType(Of DataRow)().ToList()
            columnCache.Add(name, New SortedSet(Of String)(rows.Select(Function(r) r.Field(Of String)("ColumnName"))))
        End SyncLock
    End Sub

    <Extension>
    Public Function HasColumn(name As String, column As String) As Boolean
        SyncLock lockObject
            Dim cols As New SortedSet(Of String)
            If Not columnCache.TryGetValue(name, cols) Then
                Return False
            End If

            Return cols.Contains(column)
        End SyncLock
    End Function
End Module

Here's the thing. I have some unit tests that test the code that leverages the HasColumn function. I set these tests up like this:

dataReader.Setup(Function(x) x(field)).Returns(val)

' setup the schema table
Dim table As New DataTable()
table.Columns.Add("ColumnName", GetType(String))
If setupTable Then
    table.Rows.Add(field)
End If
dataReader.Setup(Function(x) x.GetSchemaTable()) _
    .Returns(table)

dataReader.Object.CacheSchemaTable("table")

Then they test this function:

Dim typeName = GetType(T).Name
Debug.WriteLine($"IDataReader_Value({schemaTableName}.{column})")

If Not schemaTableName.HasColumn(column) Then
    Debug.WriteLine($"Could not find column {column}; returning default value.")
    Return typeName.DefaultValue()
End If

Dim input = dr(column)
Debug.WriteLine($"Found column {column}; returning value {input}.")
Return Value(Of T)(input)

You can see here where I hit the HasColumn method. Here's the thing. If I execute these tests individually they succeed; however, they fail if I execute the entire set of tests.

Clearly there is a thread-safety issue here, but I can't for the life of me figure out what I did wrong. Can somebody help me see where I went wrong?

The output of a test when it's failing is:

Test Name:  IDataReader_ValueBoolean
Test Outcome:   Failed
Result Message: Assert.AreEqual failed. Expected:<True>. Actual:<False>.
Result StandardOutput:  
Debug Trace:
IDataReader_Value(table.field)
Could not find column field; returning default value.

The output of a test when it succeeds is:

Test Name:  IDataReader_ValueBoolean
Test Outcome:   Passed
Result StandardOutput:  
Debug Trace:
IDataReader_Value(table.field)
Found column field; returning value True.

Upvotes: 0

Views: 148

Answers (1)

Mike Perrenoud
Mike Perrenoud

Reputation: 67898

I figured it out. The issue wasn't with SyncLock, it was just with my logic. Each test is hitting a different problem. Some are testing the missing column, while some are expecting it to exist. Because of this I needed to be able to update the cache.

Here is the new logic:

SyncLock lockObject
    Debug.WriteLine($"Caching schema table {name}.")
    Dim rows As New List(Of DataRow)
    If Not columnCache.ContainsKey(name) Then
        Debug.WriteLine($"Adding cache key for {name}.")
        columnCache.Add(name, New SortedSet(Of String)())
    End If

    rows = dataReader.GetSchemaTable().Rows.OfType(Of DataRow)().ToList()
    Debug.WriteLine($"Schema table rows count: {rows.Count}")
    columnCache(name) = New SortedSet(Of String)(rows.Select(Function(r) r.Field(Of String)("ColumnName")))
    Debug.WriteLine($"Successfully cached {name}.")
End SyncLock

Upvotes: 1

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