Chapter 10 Channels and select

This chapter has an accompanying online talk: YouTube, Google Slides.

• 10.1 Channels and the Engineering of CSP
• 10.2 hchan: The Internal Structure of a Channel
• 10.3 Send, Receive, and Direct Handoff
• 10.4 The Semantics of Closing
• 10.5 The Implementation of select
• 10.6 The Memory Model and the Lock-Free Evolution
• 10.7 Engineering Practice and Cross-Language Comparison

“Do not communicate by sharing memory; instead, share memory by communicating” is the most widely repeated maxim of Go concurrency, and the channel is its realization in the language: a send paired with a receive both transfers data and synchronizes two goroutines. The intellectual roots of CSP are covered in 1.3 Communicating Sequential Processes. This chapter looks at how channels and select are implemented in the runtime: the layout of a channel in memory, how one send and one receive complete between two goroutines, how closing notifies every waiter, how select picks one of several communications fairly and without deadlock, and how these operations satisfy the requirements of the memory model.

Pike’s proverb fixes the role of the channel: it is not another kind of lock but a means of organizing cooperation among goroutines. Notably, the runtime implements channels with the very mutex that the other half of the proverb names. The chapter starts from the semantics and data structure of channels, then covers sends and receives, closing, and the implementation of select; 10.6 explains why channels are still a lock-based structure, and 10.7 discusses when to use a channel and when a lock, and compares channels with similar mechanisms in other languages.