TimoYang

Is Parallel.For a Thread that isn't BackGround=True？

i do not know ... however, if you're interested, the .NET Framework 4 is now open source since around 2008:

http://www.hanselman.com/blog/ASPNETMVC4ASPNETWebAPIAndASPNETWebPagesV2RazorNowAllOpenSourceWithContributions.aspx

http://weblogs.asp.net/scottgu/archive/2008/01/16/net-framework-library-source-code-now-available.aspx

http://weblogs.asp.net/scottgu/archive/2007/10/03/releasing-the-source-code-for-the-net-framework-libraries.aspx

http://blogs.msdn.com/b/sburke/archive/2008/01/16/configuring-visual-studio-to-debug-net-framework-source-code.aspx

http://www.codeproject.com/Articles/23552/NET-Mass-Downloader-Download-the-NET-Framework-So
   "With this tool you can download whole .NET Framework source code at once, and enjoy offline browsing.
    With it, you can have whole the source code without any Visual Studio product installed"

vs2010:  http://www.codeproject.com/Articles/93423/Step-Into-NET-Framework-4-0-Source-Code
               "How to configure your Visual Studio 2010 to step into the source code of .NET Framework 4.0."

http://referencesource.microsoft.com/

http://referencesource.microsoft.com/netframework.aspx  "Available Source Code Components"

g.