Part III Concurrency

• Chapter 9 The goroutine Scheduler
• Chapter 10 Channels and select
• Chapter 11 Synchronization Primitives and Patterns

Go supports concurrency directly in the language: the go statement starts a goroutine, channels pass values between goroutines, and select picks one of several communication operations to proceed. These constructs descend from Hoare’s Communicating Sequential Processes (1.3). The proverb above comes from Pike’s talk at Gopherfest SV in 2015 and summarizes the matching programming style: let ownership of data move between goroutines along with messages, rather than having several goroutines access the same state under a lock.

This part discusses the implementation of these constructs from the bottom up. Chapter 9 covers how the scheduler multiplexes a large number of goroutines onto a small number of operating system threads, together with the supporting mechanisms of preemption, system monitoring, network polling and timers. Chapter 10 covers the data structures behind channels and select, and the implementation of send, receive, close and multiway selection. Chapter 11 covers the synchronization primitives of the sync package (mutexes, condition variables, wait groups), as well as atomic operations, contexts and the Go memory model. Communication and shared memory are not mutually exclusive: a channel is itself protected by a lock, and in many situations a mutex remains the more direct choice. Only by understanding the implementation and cost of both can one choose well for a concrete problem.