With channel:

ch := make(chan int)
go func() {
    ch <- 42
}()
result := <-ch

Instructions

Step 1: Choose Concurrency Pattern

Simple parallel execution:

var wg sync.WaitGroup

for i := 0; i < 10; i++ {
    wg.Add(1)
    go func(id int) {
        defer wg.Done()
        process(id)
    }(i)
}

wg.Wait()

Worker pool:

jobs := make(chan Job, 100)
results := make(chan Result, 100)

// Start workers
for w := 0; w < numWorkers; w++ {
    go worker(jobs, results)
}

// Send jobs
for _, job := range allJobs {
    jobs <- job
}
close(jobs)

// Collect results
for range allJobs {
    result := <-results
    handleResult(result)
}

Pipeline:

// Stage 1: Generate
gen := func() <-chan int {
    out := make(chan int)
    go func() {
        defer close(out)
        for i := 0; i < 10; i++ {
            out <- i
        }
    }()
    return out
}

// Stage 2: Process
process := func(in <-chan int) <-chan int {
    out := make(chan int)
    go func() {
        defer close(out)
        for n := range in {
            out <- n * 2
        }
    }()
    return out
}

// Use pipeline
for result := range process(gen()) {
    fmt.Println(result)
}

Step 2: Implement Channel Communication

Unbuffered channel (synchronous):

ch := make(chan int)

go func() {
    ch <- 42 // Blocks until received
}()

value := <-ch // Blocks until sent

Buffered channel (asynchronous):

ch := make(chan int, 10) // Buffer of 10

ch <- 1 // Doesn't block until buffer full
ch <- 2

value := <-ch // Doesn't block if buffer has data

Select for multiple channels:

select {
case msg := <-ch1:
    fmt.Println("Received from ch1:", msg)
case msg := <-ch2:
    fmt.Println("Received from ch2:", msg)
case <-time.After(time.Second):
    fmt.Println("Timeout")
}

Step 3: Use Synchronization Primitives

Mutex for shared state:

type SafeCounter struct {
    mu    sync.Mutex
    count int
}

func (c *SafeCounter) Inc() {
    c.mu.Lock()
    defer c.mu.Unlock()
    c.count++
}

func (c *SafeCounter) Value() int {
    c.mu.Lock()
    defer c.mu.Unlock()
    return c.count
}

RWMutex for read-heavy workloads:

type Cache struct {
    mu    sync.RWMutex
    items map[string]string
}

func (c *Cache) Get(key string) (string, bool) {
    c.mu.RLock()
    defer c.mu.RUnlock()
    val, ok := c.items[key]
    return val, ok
}

func (c *Cache) Set(key, value string) {
    c.mu.Lock()
    defer c.mu.Unlock()
    c.items[key] = value
}

WaitGroup for goroutine coordination:

var wg sync.WaitGroup

for i := 0; i < 5; i++ {
    wg.Add(1)
    go func(id int) {
        defer wg.Done()
        doWork(id)
    }(i)
}

wg.Wait() // Wait for all goroutines

Step 4: Implement Context for Cancellation

Basic context usage:

ctx, cancel := context.WithCancel(context.Background())
defer cancel()

go func() {
    for {
        select {
        case <-ctx.Done():
            return // Exit when cancelled
        default:
            doWork()
        }
    }
}()

// Cancel when done
cancel()

With timeout:

ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
defer cancel()

result, err := doWorkWithContext(ctx)
if err == context.DeadlineExceeded {
    fmt.Println("Operation timed out")
}

Propagate context:

func ProcessRequest(ctx context.Context, req Request) error {
    // Pass context to all operations
    data, err := fetchData(ctx, req.ID)
    if err != nil {
        return err
    }
    
    return saveData(ctx, data)
}

Common Patterns

Fan-Out/Fan-In

func fanOut(in <-chan int, n int) []<-chan int {
    outs := make([]<-chan int, n)
    for i := 0; i < n; i++ {
        outs[i] = process(in)
    }
    return outs
}

func fanIn(channels ...<-chan int) <-chan int {
    out := make(chan int)
    var wg sync.WaitGroup
    
    for _, ch := range channels {
        wg.Add(1)
        go func(c <-chan int) {
            defer wg.Done()
            for n := range c {
                out <- n
            }
        }(ch)
    }
    
    go func() {
        wg.Wait()
        close(out)
    }()
    
    return out
}

Rate Limiting

func rateLimiter(rate time.Duration) <-chan time.Time {
    return time.Tick(rate)
}

limiter := rateLimiter(time.Second / 10) // 10 per second

for range limiter {
    go processItem()
}

Timeout Pattern

func doWithTimeout(timeout time.Duration) error {
    done := make(chan error, 1)
    
    go func() {
        done <- doWork()
    }()
    
    select {
    case err := <-done:
        return err
    case <-time.After(timeout):
        return errors.New("timeout")
    }
}

Error Group

import "golang.org/x/sync/errgroup"

func processAll(items []Item) error {
    g := new(errgroup.Group)
    
    for _, item := range items {
        item := item // Capture for goroutine
        g.Go(func() error {
            return process(item)
        })
    }
    
    return g.Wait() // Returns first error
}

Advanced

For detailed patterns:

Channels - Channel patterns and best practices
Sync - Synchronization primitives
Context - Context usage and propagation

Troubleshooting

Goroutine leaks:

Always ensure goroutines can exit
Use context for cancellation
Close channels when done

Deadlocks:

Avoid circular channel dependencies
Don't send on unbuffered channel without receiver
Use select with timeout

Race conditions:

Use go run -race to detect
Protect shared state with mutexes
Prefer channels for communication

Performance issues:

Don't create too many goroutines
Use worker pools for bounded concurrency
Profile with pprof

Best Practices

Don't communicate by sharing memory; share memory by communicating
Always handle goroutine cleanup: Use context, defer, or done channels
Avoid goroutine leaks: Ensure all goroutines can exit
Use buffered channels carefully: Can hide synchronization issues
Prefer sync.WaitGroup: For waiting on multiple goroutines
Pass context: Propagate cancellation through call stack
Close channels from sender: Never close from receiver
Check channel closure: Use val, ok := <-ch

goroutine-patterns

Goroutine Patterns

Quick Start