The Go Programming Language

9.1 Race Conditions

In a sequential program, that is, a program with only one goroutine, the steps of the program happen in the familiar execution order determined by the program logic. For instance, in a sequence of statements, the first one happens before the second one, and so on. In a program with two or more goroutines, the steps within each goroutine happen in the familiar order, but in general we don’t know whether an event x in one goroutine happens before an event y in another goroutine, or happens after it, or is simultaneous with it. When we cannot confidently say that one event happens before the other, then the events x and y are concurrent.

Consider a function that works correctly in a sequential program. That function is ...