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topics/go/concurrency/goroutines/README.md

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Goroutines

Goroutines are functions that are created and scheduled to be run independently by the Go scheduler. The Go scheduler is responsible for the management and execution of goroutines.

Notes

  • Goroutines are functions that are scheduled to run independently.
  • We must always maintain an account of running goroutines and shutdown cleanly.
  • Concurrency is not parallelism.
    • Concurrency is about dealing with lots of things at once.
    • Parallelism is about doing lots of things at once.

"Parallelism is about physically doing two or more things at the same time. Concurrency is about undefined, out of order, execution." - William Kennedy

"By default, goroutines shouldn't outlive the function they were created from. this forces you into a extremely good design posture." - Peter Bourgon

Design Guidelines

Diagrams

How the scheduler works.

Scheduling In Go - Part I - William Kennedy
Scheduling In Go - Part II - William Kennedy
Scheduler Tracing In Go - William Kennedy
Advanced Go Concurrency Patterns - Sameer Ajmani
Go Concurrency Patterns: Context - Sameer Ajmani
Concurrency is not parallelism - Rob Pike
Go, for Distributed Systems - Russ Cox
Go 1.5 GOMAXPROCS Default
Concurrency, Goroutines and GOMAXPROCS - William Kennedy
The Linux Scheduler: a Decade of Wasted Cores
Explanation of the Scheduler
15 Years of Concurrency - Joe Duffy
How does the golang scheduler work? - Ian Lance Taylor
The Scheduler Saga - Kavya Joshi

Code Review

Goroutines and concurrency (Go Playground)
Goroutine time slicing (Go Playground)
Goroutines and parallelism (Go Playground)

Exercises

Exercise 1

Part A Create a program that declares two anonymous functions. One that counts down from 100 to 0 and one that counts up from 0 to 100. Display each number with an unique identifier for each goroutine. Then create goroutines from these functions and don't let main return until the goroutines complete.

Part B Run the program in parallel.

Template (Go Playground) | Answer (Go Playground)

All material is licensed under the Apache License Version 2.0, January 2004.