how does CLR run beginXXX in a thread pool thread?
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I try to figure out how CLR put asynchronous operations BeginXXX into thread pool's queue.
and which ThreadPool's API is called.
But I did not find anything when I pokeed aroud BeginRead() in System.IO.Stream  
and BeginExecuteReader() in System.Data.Sqlclient.SqlCommand by Reflector 6.