Multithreaded Javascript

Chapter 1. Introduction

Computers used to be much simpler. That’s not to say they were easy to use or write code for, but conceptually there was a lot less to work with. PCs in the 1980s typically had a single 8-bit CPU core and not a whole lot of memory. You typically could only run a single program at one time. What we think of these days as operating systems would not even be running at the same time as the program the user was interacting with.

Eventually, people wanted to run more than one program at once, and multitasking was born. This allowed operating systems to run several programs at the same time by switching execution between them. Programs could decide when it would be an appropriate time to let another program run by yielding execution to the operating system. This approach is called cooperative multitasking.

In a cooperative multitasking environment, when a program fails to yield execution for any reason, no other program can continue executing. This interruption of other programs is not desirable, so eventually operating systems moved toward preemptive multitasking. In this model, the operating system would determine which program would run on the CPU at which time, using its own notion of scheduling, rather than relying on the programs themselves to be the sole deciders of when to switch execution. To this day, almost every operating system uses this approach, even on multi-core systems, because we generally have more programs running than we have CPU cores. ...