Go Concurrency

You are a Go concurrency expert. The user wants to implement goroutines, channels, and concurrency patterns efficiently and safely.

What to check first

• Run go version to verify Go 1.18+ is installed (generics support for advanced patterns)
• Check if you're using buffered or unbuffered channels — this determines blocking behavior
• Verify context package imports for cancellation and timeouts

Steps

1. Create a goroutine using go functionName() syntax — this spawns a lightweight thread managed by the Go runtime
2. Define a channel type with make(chan Type) or make(chan Type, bufferSize) for buffered channels
3. Send data to a channel with channel <- value and receive with value := <-channel
4. Use select statement to multiplex on multiple channels with case <-channelA: and case <-channelB:
5. Implement worker pools by launching N goroutines that read from a shared work channel
6. Add context cancellation with ctx, cancel := context.WithCancel(context.Background()) to all goroutines
7. Use sync.WaitGroup to track goroutine completion with .Add(), .Done(), and .Wait() methods
8. Guard shared state with sync.Mutex using .Lock() and .Unlock() around critical sections

Code

package main

import (
	"context"
	"fmt"
	"sync"
	"time"
)

// Worker pool pattern with channels and goroutines
func workerPool(jobs <-chan int, results chan<- string, workerID int) {
	for job := range jobs {
		result := fmt.Sprintf("Worker %d processed job %d", workerID, job)
		results <- result
		time.Sleep(100 * time.Millisecond)
	}
}

// Fan-out/fan-in pattern
func merge(ctx context.Context, channels ...<-chan string) <-chan string {
	var wg sync.WaitGroup
	out := make(chan string)

	output := func(ch <-chan string) {
		defer wg.Done()
		for {
			select {
			case <-ctx.Done():
				return
			case val, ok := <-ch:
				if !ok {
					return
				}
				select {
				case out <- val:
				case <-ctx.Done():
					return
				}
			}
		}
	}

	wg.Add(len(channels))
	for _, ch := range channels {
		go output(ch)
	}

	go func() {
		wg.Wait()
		close(out)
	}()

	return out
}

// Rate limiter using time.Ticker
func rateLimiter(limit int) <-chan time.Time {
	return time.Tick(time.Second / time.Duration(limit))
}

func

Note: this example was truncated in the source. See the GitHub repo for the latest full version.

Common Pitfalls

• Treating this skill as a one-shot solution — most workflows need iteration and verification
• Skipping the verification steps — you don't know it worked until you measure
• Applying this skill without understanding the underlying problem — read the related docs first

When NOT to Use This Skill

• When a simpler manual approach would take less than 10 minutes
• On critical production systems without testing in staging first
• When you don't have permission or authorization to make these changes

How to Verify It Worked

• Run the verification steps documented above
• Compare the output against your expected baseline
• Check logs for any warnings or errors — silent failures are the worst kind

Production Considerations

• Test in staging before deploying to production
• Have a rollback plan — every change should be reversible
• Monitor the affected systems for at least 24 hours after the change