Code-Memo

Concurrency and parallelism

Concurrency is dealing with many things at once; parallelism is doing many things at once. Go’s goroutines are cheap coroutines multiplexed onto OS threads by the runtime.

Goroutine

go func() {
	// runs concurrently
}()

sync.Mutex

Protect shared mutable state.

var mu sync.Mutex
var balance int

func deposit(amount int) {
	mu.Lock()
	defer mu.Unlock()
	balance += amount
}

sync.WaitGroup

Wait for a group of goroutines.

var wg sync.WaitGroup
for i := 0; i < 3; i++ {
	wg.Add(1)
	go func(id int) {
		defer wg.Done()
		work(id)
	}(i)
}
wg.Wait()

sync.Once

Initialize exactly once.

var once sync.Once
once.Do(setup)

GOMAXPROCS

runtime.GOMAXPROCS controls OS threads running Go code in parallel; default is usually sensible on modern Go.

Data races

The race detector (go test -race) finds unsynchronized accesses. Prefer channels or mutexes; do not rely on “it usually works”.

Happens-before

Memory visibility follows happens-before rules: channel sends/receives, sync primitives, and go statement establish ordering. Read the spec when optimizing lock-free code.