Chapter 7. Threading

Threading is the creation and management of multiple units of execution within a single process. Threading is a significant source of programming error, through the introduction of data races and deadlocks. The topic of threading can—and indeed does—fill whole books. Those works tend to focus on the myriad interfaces in a particular threading library. While we will cover the basics of the Linux threading API, the goal of this chapter is to go meta: How does threading fit into the system programmer’s overall toolkit? Why use threads—and, more importantly, why not? What design patterns help us conceptualize and build threading applications? And, finally, what are data races and how can we prevent them?

Binaries, Processes, and Threads

Binaries are dormant programs residing on a storage medium, compiled to a format accessible by a given operating system and machine architecture, ready to execute but not yet in motion. Processes are the operating system abstraction representing those binaries in action: the loaded binary, virtualized memory, kernel resources such as open files, an associated user, and so on. Threads are the unit of execution within a process: a virtualized processor, a stack, and program state. Put another way, processes are running binaries and threads are the smallest unit of execution schedulable by an operating system’s process scheduler.

A process contains one or more threads. If a process contains but one thread, there is only a single unit of ...

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