What does STAThread do

Question

I am learning C  3 5 and I want to know what  STAThread  does in our programs

User · Answer

The STAThreadAttribute marks a thread to use the Single-Threaded COM Apartment if COM is needed. By default, .NET won't initialize COM at all. It's only when COM is needed, like when a COM object or COM Control is created or when drag 'n' drop is needed, that COM is initialized. When that happens, .NET calls the underlying CoInitializeEx function, which takes a flag indicating whether to join the thread to a multi-threaded or single-threaded apartment.

Read more info here (Archived, June 2009)

and

Why is STAThread required?

User · Answer

The STAThreadAttribute is essentially a requirement for the Windows message pump to communicate with COM components  Although core Windows Forms does not use COM  many components of the OS such as system dialogs do use this technology  MSDN explains the reason in slightly more detail   STAThreadAttribute indicates that the COM threading model for the application is single-threaded apartment  This attribute must be present on the entry point of any application that uses Windows Forms  if it is omitted  the Windows components might not work correctly  If the attribute is not present  the application uses the multithreaded apartment model  which is not supported for Windows Forms   This blog post  Why is STAThread required   also explains the requirement quite well  If you want a more in-depth view as to how the threading model works at the CLR level  see this MSDN Magazine article from June 2004  Archived  Apr  2009

User · Answer

It tells the compiler that you re in a Single Thread Apartment model   This is an evil COM thing  it s usually used for Windows Forms  GUI s  as that uses Win32 for its drawing  which is implemented as STA   If you are using something that s STA model from multiple threads then you get corrupted objects   This is why you have to invoke onto the Gui from another thread  if you ve done any forms coding    Basically don t worry about it  just accept that Windows GUI threads must be marked as STA otherwise weird stuff happens

[c#] What does [STAThread] do?

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