Question

我有一个循环，可以创建几个线程：

SomeClass..

Dim someNumber As Integer = 0
Dim somethingElse As Integer = 10
Dim myThread(500) As System.Threading.Thread

For i As Integer = 0 To 500
    someNumber += 1
    somethingElse += 10

    myThread(i) = New Thread(Sub() myThreadFunction(someNumber, somethingElse))
    myThread(i).Start()
Next

For j As Integer = 0 To 500
    myThread(j).Join()
Next

Sub myThreadFunction(ByVal someNumber As Integer, ByRef somethingElse As Integer)

    DoStuff

End Sub

现在我的问题是，有时我得到传递给myThreadFunction的错误值，通常是在循环的下一次迭代中应该传递的值。

我做错了什么，有更好的方法吗？

Answer 1

这是因为lambda在错误的范围内关闭了变量。 Eric Lippert在Closing over the loop variable considered harmful中详细描述了这个问题。

要使其工作，您需要在适当的范围内引入临时变量：

For i As Integer = 0 To 500
    someNumber += 1
    somethingElse += 10

    ' Make some locally scoped variables
    Dim temp1 As Integer = someNumber
    Dim temp2 As Integer = somethingElse 

    ' Use the temporaries
    myThread(i) = New Thread(Sub() myThreadFunction(temp1, temp2))
    myThread(i).Start()
Next

另请注意：我建议您还考虑使用ThreadPool或Task Parallel Library而不是手动创建线程。对于大多数情况，这通常是更好的方法。

将多个参数传递给多个线程

1 个答案: