The Windows messaging subsystem

All Windows-based applications are event-driven. This means that they don't make explicit calls to functions in the OS APIs. Instead, they wait for the system to pass any input to them. So it's the system that's the one in charge of providing that input.

The system's kernel is in charge of converting hardware events (users' clicks, keyboard entries, touch screen gestures, the arrival of bytes in a communication's port, and so on) into software events, which take the form of messages addressed to a software target: a button in a window, a textbox in a form, and so on. After all, this is the soul of the Event-driven Programming paradigm.

I'll start with a section that deals with how .NET can use low-level resources of the operating system, in other words, how our applications can communicate and use the core functionality of our operating system, despite being coded using distinct models, with distinct data types and calling conventions. This technique permits...