Parallel.ForEach本地存儲

Question

我最近將For Each循環更改爲Parallel.ForEach循環。我擔心一個對象在循環外部被聲明，但是在循環中迭代時被賦值。這是簡化的代碼。

Dim results As ModelResults 
Dim noResultsModel As New List(Of ModelResults) 
Dim lock As New Object 
Parallel.ForEach(_modelEngines, 
    Sub(model) 

    results = model.Execute 

    If results IsNot Nothing Then 

     SyncLock lock 
      noResultsModel.Add(results) 
     End SyncLock 

    End If 

    results = Nothing 

End Sub) 

是否存在與結果對象的潛在競爭條件？如果我將結果聲明移至for循環，會不會有所不同？

Answer 1

是的，肯定是有競爭條件與循環外聲明的變量：

Thread 1: results = model.Execute ' results are from Thread1's current modelEngine 
Thread 2: results = model.Execute ' results are from Thread2's current modelEngine 
Thread 2: If results IsNot Nothing Then ' results are from Thread2's current modelEngine 
Thread 1: If results IsNot Nothing Then ' results are from Thread2's current modelEngine(!) 

只是裏面移動它，我不明白你爲什麼會想反正聲明它的外循環。