CODEWITHSUNDEEP
c#
user133466
user133466

Reputation: 3415

What does it mean when someone says "C# program should communicate with unmanaged COM code using the Single Threading Apartment"

what's an unmanaged COM code? and Single Threading Apartment? Thank you!

Upvotes: 1

Views: 368

Answers (5)

P.K
P.K

Reputation: 19147

Look at this answer on stackoverflow to understand about STA vs MTA: Single-Threaded Apartments vs Multi-Threaded Apartments

my 2 cents: AFAIK (gurus, correct me if I am wrong) with windows threading model, the GUI has always been single threaded and MS just wanted to continue with this in .net and hence the STA attribute on your main thread. Your worker threads can be MTA. But, your main thread(GUI thread) has to be STA to allow it to communicate with other programs, say built in COM.

Upvotes: 1

Steven A. Lowe
Steven A. Lowe

Reputation: 61242

it means your main method should have the [STAThread] attribute in front of it, e.g.

[STAThread]
public void Main(string[] args) { ... }

this forces your main thread to the apartment-threaded model, which is what COM components require

what it all really means in excruciating technical detail may or may not matter if the above just works ;-)

Upvotes: 1

ajh1138
ajh1138

Reputation: 566

Like Sinan said, it's a pretty complicated thing. But I'll try to provide some insight from a historical perspective.

Prior to .Net, COM was Microsoft's way of providing developers with a way to build frequently-used objects and get them to work between multiple programs and instances of programs. It sucked. It would get stuck all the time. It would leak memory. It would crash servers. Look up "DLL Hell" sometime. You could completely unregister a DLL from your server then register a new version of it, and guess what? COM would sometimes stubbornly hold on to your DLL to the point where even a reboot wouldn't kill it.

Then .Net came along and one of the great things about it was that it solved a great many problems that COM had. Anything that .Net has direct control of (that is, anything built within/using the .Net framework) is called "managed" code. "Unmanaged" code is anything else.

When you hear something like "C# program should communicate with unmanaged COM code using the Single Threading Apartment” it's .Net's way of saying "If you're going to make me work with your nasty, old-school, dangerous, caveman COM object, then you need to do it in a way that won't kill me when it crashes."

Upvotes: 1

Martin Cote
Martin Cote

Reputation: 29882

To make a long story short:

Unmanaged COM code means that there's no garbage collector available for that code. The COM code deal with its own memory, the .NET garbage collector shouldn't try to collect that memory.

The single threaded apartment is a model in which every COM messages are serialized/deserialized between objects. The messages are pumped through the windows messaging model, so that the COM objects don't need to care about thread-safety issues. In the multi-threaded apartment, the messages sent to an object can occur at any time, so that the objects must be thread-safe.

This is a very simplified explanation. More details about the single-threaded apartment here.

Upvotes: 6

Sinan Ünür
Sinan Ünür

Reputation: 118156

It means, "here are the key phrases you should look up and understand". No, this is not a snide remark. These concepts are involved and complicated and a single textbox is not the right place to try to explain them.

You can also ask that someone what s/he meant.

In the mean time, you could read An Overview of Managed/Unmanaged Code Interoperability and Processes, Threads, and Apartments.

Upvotes: 8

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