I have heard that C++ offers no native support for multithreading. I assume that multithreaded C++ apps depended on managed code for multithreading; that is, for example, a Visual C++ app used MFC or .NET or something along those lines to provide multithreading capability. I further assume that some or all of those managed-code capabilities are unavailable to unmanaged applications. But I have read about unmanaged multithreaded applications. How is this possible? Which of my assumptions is false?
It is wholly up to the operating system to provide support for multi-threading. On Windows, the necessary functionality is available via the Win32 API. Frameworks such as MFC provide wrappers over the low-level threading functions to simplify things, while of course .NET/CLR has its own managed interface for accessing Win32 multi-threading capabilities.
A good explanation is offerred in this article (Multithreading in C++).
Why Doesn’t C++ Contain Built-In Support for Multithreading?
C++ does not contain any built-in support for multithreaded applications. Instead, it relies entirely upon the operating system to provide this feature. Given that both Java and C# provide built-in support for multithreading, it is natural to ask why this isn’t also the case for C++. The answers are efficiency, control, and the range of applications to which C++ is applied. Let’s examine each.
By not building in support for multithreading, C++ does not attempt to define a “one size fits all” solution. Instead, C++ allows you to directly utilize the multithreading features provided by the operating system. This approach means that your programs can be multithreaded in the most efficient means supported by the execution environment. Because many multitasking environments offer rich support for multithreading, being able to access that support is crucial to the creation of high-performance, multithreaded programs.