An apartment is a logical "container" for threads. Apartments come in two sizes – "single" and "multi".
An STA contains just one thread; MTA can contain any number of threads.
· Apartment threading is an automatic Thread-Safety System, closely allied to COM – Microsoft's legacy.
· Though .NET largely breaks free of this legacy models, there are times when it still crops up because of the need to interoperate with older Win32 APIs.
· Apartment threading is most relevant to Windows Forms, because much of Windows Forms uses or wraps the long-standing Win32 API.
A .NET thread is By Default Allocated MTA, unless one requests a STA as follows:
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Thread t = new Thread (...);
Otherwise one can also request that the main thread join a STA using the STAThread attribute on the main method:.
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// Code Here
· Apartments have no effect while being with STA and executing pure .NET code .
· In other words, two threads with an apartment state of STA can simultaneously call the same method on the same object, and no automatic marshalling or locking will take place.
· Only when execution hits unmanaged code can they kick in.
The types in the System.Windows.Forms namespace extensively call Win32 code designed to work in a STA. For this reason, a Windows Forms program should have have the [STAThread] attribute on its main method, otherwise one of two things will occur upon reaching Win32 UI code:
· It will marshal over to a STA
· It will crash.
Hope this helps.
Thanks & Regards,
Arun Manglick || Senior Tech Lead