Go

In this guide, we introduce some knowledge about Go.

Goroutines

• Go is a message-oriented programming language.
• A goroutine is a lightweight thread of execution. It is completely handled by the Go runtime, and does not incur any system-level context switch, etc.
• The scheduler in Go is based on the CSP (communicating sequential process) model. However, it has been improved to become the GMP (goroutine, machine and processor) model.
  • Each machine corresponds to an actual thread in the system kernel.
  • Each machine will be binded with a processor (thus 1-to-1 relationship mapping), with the context needed to process user-level logical code.
  • Each processor is connected to multiple goroutines, one running while the others waiting.
• Communication between different goroutines happens via channels. Channels can also be used for synchronization.
  • select is like the channel-based version of switch. It can be used to wait on multiple channels.
    • select can be used together with time.After to implement a timeout functionality with a fallback function.
  • However, if you need to wait for the completion of all n channels, you probably want to use a WaitGroup (i.e., implemented via a mutex).
• Each processor has a schedule function that schedules goroutines from different queues:
  • A global queue across all processors;
  • Its local queue;
  • The local queue from other processors.

defer keyword

• defer is a keyword in Go that can be used to execute something when the surrounding function returns.
• It is useful to use defer to close resources such as opened files, channels, etc.
• If there are multiple defer statements, they will be executed in the reverse order (i.e., first in last out) when the surrounding function returns.

Go Garbage Collector (GC)

• The development of Go’s GC is an ever evolving journey:
  • Since Go 1.1: stop the world (STW)， a.k.a. write barrier
  • Since Go 1.3: mark STW & sweep
  • Since Go 1.5: tri-coloring marking
  • Since Go 1.8: hybrid write barrier