Skip to Main Content
C# in a Nutshell
book

C# in a Nutshell

by Ben Albahari, Ted Neward, Peter Drayton
March 2002
Intermediate to advanced content levelIntermediate to advanced
864 pages
31h 8m
English
O'Reilly Media, Inc.
Content preview from C# in a Nutshell

Name

ApartmentState

Synopsis

This type is entirely unnecessary for “normal” .NET code; it is needed only for COM interoperability capability.

Apartments are a COM-threading construct. There are two threading apartments: single-threaded (STA) and multithreaded (MTA). Once a thread joins an apartment, it cannot join another one. If you want to create or access a COM object from a thread, that thread must belong to an apartment. Further, a given COM component may only be compatible with a certain apartment state.

What if an STA thread needs to call a method on a COM object that is only compatible with MTA threads? In that case, a different thread that is already in the MTA state must service the request. The COM Service Control Manager either creates a new thread or uses one allocated for servicing remote procedure calls to accomplish this.

Threads in an MTA apartment cannot directly access STA threads either. Instead, the STA thread contains a message sink, and the method is invoked when the thread in that apartment is free. .NET objects do away with this requirement; however, if some of the threads call COM objects, they must first join an apartment. The Thread class usually handles this automatically, but you can join an apartment directly by assigning a parameter from this enumeration to the Thread.ApartmentState property. Unknown indicates that the thread has not joined an apartment.

public enum ApartmentState {
   STA = 0,
   MTA = 1,
   Unknown = 2
}

Hierarchy

System.ObjectSystem.ValueType ...

Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Start your free trial

You might also like

C# 8.0 in a Nutshell

C# 8.0 in a Nutshell

Joseph Albahari, Eric Johannsen
C# 10 in a Nutshell

C# 10 in a Nutshell

Joseph Albahari
C# in a Nutshell, Second Edition

C# in a Nutshell, Second Edition

Peter Drayton, Ben Albahari, Ted Neward
Code like a Pro in C#

Code like a Pro in C#

Jort Rodenburg

Publisher Resources

ISBN: 0596001819Catalog PageErrata