concurrency.debug.md

Overview

1. Debugging goroutines
2. Debugging concurrent & parallel go programs

Symptoms

1. Hanging goroutines (your program should end but some goroutines are stuck)
2. Unexpected variable values (Race conditions)

Anti-patterns

1. littering your code with log statements
2. Adding extra complexity
3. Adding locks/mutexes

Solution-1: Run locally

1. Set env var: GOTRACEBACK="all"
2. Run the program
3. Get your process id
4. Wait for it to reach a point of non-responsiveness
5. Run kill -3 <pid>
6. See the live goroutines in the console
7. ag/ripgrep/grep for your source directory
8. Use the file and line numbers to see where goroutines are stuck

Solution-2: Add observability (works locally and on servers)

1. See tracing doc

Solution-3: Run locally and Use a debugger

1. See https://www.jetbrains.com/help/go/debugging-code.html

Solution-4: Use the race detector

1. https://go.dev/blog/race-detector
2. https://go.dev/doc/articles/race_detector
3. https://yourbasic.org/golang/detect-data-races/

Solution-5: Add tests

1. Writing test friendly code forces you to write modular code
2. Modular code is simple to reason about
3. Tests can help you pin-point issues
4. see unit test doc and e2e doc

Solution-6: Follow best practices

1. Use a static analyzer (like golangci-lint or goland's inspections or sonarqube)
2. static analyzers can help you find and fix anti-patterns
3. Some anti-patterns cause concurrency issues, others make it harder to solve them

Solution-7: Use the tools correctly

1. Channels, Goroutines, select blocks and mutexes all have a few gotchas related to correct usage
2. Use your resources to learn idiomatic usage (books, articles, youtube videos, ai tools, Goland docs, ...)