Summary 61 The highest level of abstraction This is simple, but I wanted to add this just for completeness. Rust standard library wraps the calls to the underlying OS APIs for us, so we don't have to care about what syscalls to invoke. fn main() { println!("Hello world from the standard library"); } Congratulations! Y ou've now written the same syscall using three levels of abstraction. Y ou now know what FFI looks like, you've seen some inline assembly (which we'll cover in greater detail later), and you've made a proper syscall to print something to the console. Y ou've also seen one of the things our standard library tries to solve by wrapping these calls for different platforms so we don't have to know these syscalls to print something to the console. Summary In this chapter, we went through what OS-backed event queues are and gave a high-level overview of how they work. We also went through the defining characteristics of epoll, kqueue, and IOCP and focused on how they differ from each other. In the last half of this chapter, we introduced some examples of syscalls. We discussed raw syscalls, and “normal” syscalls so that you know what they are and have seen examples of both. We also took the opportunity to talk about abstraction levels and the advantages of relying on good abstractions when they're available to us. As a part of making system calls, you also got an introduction to Rusts FFI. Finally, we created a cross-platform abstraction. Y ou also saw some of the challenges that come with creating a unifying API that works across several operating systems. The next chapter will walk you through an example using epoll to create a simple event queue, so you get to see exactly how this works in practice. In the repository, you'll also find the same example for both Windows and mac OS, so you have that available if you ever want to implement an event queue for either of those platforms.