1.1. A (Very) Brief History of Concurrency

In the ancient past, computers didn’t have operating systems; they executed a single program from beginning to end, and that program had direct access to all the resources of the machine. Not only was it difficult to write programs that ran on the bare metal, but running only a single program at a time was an inefficient use of expensive and scarce computer resources.

Operating systems evolved to allow more than one program to run at once, running individual programs in processes: isolated, independently executing programs to which the operating system allocates resources such as memory, file handles, and security credentials. If they needed to, processes could communicate with one another through a variety of coarse-grained communication mechanisms: sockets, signal handlers, shared memory, semaphores, and files.