Parallel Programming in Go

Workshop materials for a 6-hour hands-on introduction to concurrent programming in Go, developed for Petnica Science Center 2026.

Overview

Students build a concurrent web crawler from scratch across six progressive blocks. Each block introduces a new concept and adds a layer to the same program — nothing gets thrown away. By the end, the crawler fetches pages in parallel, follows links, limits concurrency, compresses content in a pipeline, and shuts down gracefully on timeout or interrupt.

A local test server (included) simulates realistic network latency and serves a graph of HTML pages for the crawler to explore.

Concepts covered

• Goroutines — launching concurrent work and understanding why sequential I/O is wasteful
• Channels — communicating between goroutines, collecting results, directional channel types
• Select — handling multiple channel operations and timeouts
• sync.WaitGroup — waiting for a dynamic number of goroutines to finish
• sync.Mutex — protecting shared state from concurrent access
• Worker pools — capping concurrency with a fixed number of long-lived goroutines
• Pipelines — chaining independent processing stages with channels
• context.Context — propagating cancellation and timeouts through a call tree
• Race detection — using -race to surface data races that don't produce obvious wrong output

Structure

cmd/
  server/       — test server (run this before any crawler)
  1-naive/      — sequential fetcher, then goroutines with time.Sleep
  2-simple/     — channels, select, HTML link parsing
  3-recursive/  — WaitGroup, Mutex, recursive crawl
  4-workerpool/ — fixed worker pool
  5-pipeline/   — two-stage pipeline with gzip compression
  6-context/    — timeout and graceful cancellation
doc/
  plan.md       — instructor guide and block-by-block workshop plan
  server.md     — server configuration reference
  materials/    — per-block reference sheets given to students

Running

# start the test server
go run ./cmd/server

# run any crawler
go run ./cmd/4-workerpool

See doc/server.md for server configuration options.