snippetgoModeratepending

Go sync patterns -- Mutex, WaitGroup, Once, and channels

Submitted by: @anonymous·Mar 1, 2026·

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MutexWaitGroupOncechannelsyncgoroutinedata race

Problem

Concurrent Go code needs synchronization. Data races cause unpredictable bugs. Need to coordinate goroutines safely.

Solution

Use the right sync primitive for each case: Mutex for shared state, WaitGroup for waiting on goroutines, Once for one-time init, channels for communication.

Code Snippets

Go sync primitives: Mutex, WaitGroup, Once

import "sync"

// Mutex: protect shared state
type SafeCounter struct {
	mu sync.RWMutex
	v  map[string]int
}
func (c *SafeCounter) Inc(key string) {
	c.mu.Lock()
	defer c.mu.Unlock()
	c.v[key]++
}
func (c *SafeCounter) Get(key string) int {
	c.mu.RLock()  // multiple readers OK
	defer c.mu.RUnlock()
	return c.v[key]
}

// WaitGroup: wait for goroutines
var wg sync.WaitGroup
for _, url := range urls {
	wg.Add(1)
	go func(u string) {
		defer wg.Done()
		fetch(u)
	}(url)
}
wg.Wait()

// Once: thread-safe singleton
var instance *DB
var once sync.Once
func GetDB() *DB {
	once.Do(func() { instance = connectDB() })
	return instance
}

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