收集被修改; 枚举操作可能无法执行

Question

我无法理解这个错误的底部,因为它只发生在一个实例中,我找不到任何可能导致错误的代码.

我有一个3.5 Web服务,我从一个多线程的CAB客户端调用.我有一堆针对Web服务的单元测试(来自3.5和2.0代码),它工作正常.但是,在实际应用中,它在90%的时间内不起作用,而剩余的10%的时间,它决定工作.

代码:

Friend Function ExecuteSearch(ByVal query As String) As List(Of SomeObject)
    Dim searchResults As List(of Object) = _searcher.UserSearch(query)
    Return searchResults
End Function 

// In Searcher
Public Function UserSearch(ByVal query As String) As List(Of SomeObject)
    Return Translate(Search.GetResults(query))
End Function

// In Search
Public Function GetResults(ByVal query As String) As List(Of SomeObject)
    Dim service As New FinderService.FinderService()
    Dim results As New List(Of String)
    Dim serviceResults As IEnumerable(Of String) = service.Search(query)    // <-- ERRORS OUT HERE 

    results.AddRange(serviceResults)

    Return results
End Function

// In the service
Public Function Search(ByVal query As String) As IEnumerable(Of String)
        Initialize() // Initializes the _accounts variable
        Dim results As New List(of String)
        For Each account As User In _accounts
            If a bunch of conditions Then
                results.Add(account.Name)
            End IF 
        End For 

        Return results 
End Function 

断点击中了这些代码(按此顺序).出错的行在"GetResults"方法中.

任何帮助,将不胜感激.

Answer 1

啊,Heisenbugs:D

显然_accounts在循环期间被修改.你可以通过这样做来缓解它

For Each account As User In _accounts.ToList()

因此创建并枚举当前_accounts的副本,而不是可能更改的实际集合