Question

I have been trying to learn about threads via the Windows API. I ran across __declspec( thread ) from msdn, but I don’t understand what the difference is between that and CreateThread().

It sounds like you only create the thread on the object? Does that mean that if I wrote a method that does while(1); and ran that method in my main class through that object, it would do that in a separate thread? I guess my question is what is __declspec ( thread ) used for, and should I use that over CreateThread?

Sorry if my question is confusing.

Answer 1

The difference between them is huge:

• __declspec( thread ) is a storage modifier that specifies that the declared variable has local storage. That means that each thread owns its own copy of this value. Is the threaded version of globals.

  C++11 introduces thread storage modifiers by the name thread_local. Its a storage modifier, like static.

• CreateThread() is a function that will create a new thread and start running some function you specify.

  C++11 also introduces an entire threading API that you can use to write thread-aware code that will run on (almost) any platform. You can search for std::thread and std::async…

So basically they are two entirely different things, used for entirely different purposes. If you want to create a new thread using the Windows API then use CreateThread. If you want a variable to have thread_local storage using the Windows API then use __declspec( thread ). If you can use C++11, you should forget about the subtleties of the Windows API and use the Standard API instead.