Concurrency in POSIX
As we explained in the previous sections, concurrency or multitasking is a functionality provided by the kernel of an operating system. Not all kernels have been concurrent since their birth, but most of them support concurrency today. It is nice to know that the first version of Unix was not concurrent, but it gained this feature very soon after its birth.
If you remember Chapter 10, Unix – History and Architecture, we explained how single Unix specification and POSIX tried to standardize the API exposed by the shell ring in a Unix-like operating system. Concurrency has been part of these standards for a long time, and so far, it has allowed many developers to write concurrent programs for POSIX-compliant operating systems. The concurrency support in POSIX has been widely used and implemented in a vast range of operating systems, such as Linux and macOS.
Concurrency in a POSIX-compliant operating system is generally provided in two...