Chapter 5. Pthreads and UNIX

In this chapter:

Because operating systems are inherently designed to accommodate processes, not threads, system implementors must often bend tradition to introduce thread support. It’s as if we were to discover one day that the sun did not orbit the earth, but that, in reality, the earth revolves around the sun. The process is no longer central to our operating system world. Whereas it used to schedule processes, our system now schedules threads—no minor feat because, to do so, it must rototill its internal data structures and reinvent some of its most basic notions. What’s more, whereas it used to deliver signals to processes, it now must deliver signals to threads. How it selects the thread to which it delivers a given signal is yet another added complexity.

Further, the operating system has always allowed us to perform certain operations on processes that become riddles in the world of threads. If we now consider a process to be a sort of container for threads, and we recognize that all threads share their process’s address space, what happens when one of these threads launches an operation that has processwide ramifications? Does a fork result in a copy of the entire process, including all existing threads? Does an exec ...

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