Sync

Advanced · Concurrency

The sync and sync/atomic packages coordinate goroutines that share memory. Always test concurrent code with go test -race (this repo’s mise run test does) — it flags data races the eye misses.

• sync1 — sync.Mutex to guard a shared counter
• sync2 — sync.Once for run-exactly-once initialization
• sync3 — sync/atomic for a lock-free counter

Resources

• Go by Example: Mutexes
• Go by Example: Atomic Counters
• pkg.go.dev: sync · sync/atomic

Exercises

sync1 test

A sync.Mutex guards shared state so concurrent goroutines don’t race.

Show hint

Guard the critical section:

c.mu.Lock()
defer c.mu.Unlock()
c.n++

Source

sync2 test

sync.Once runs a function exactly once, even when called from many goroutines.

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sync.Once.Do runs its function only the first time it is called:

c.once.Do(func() { c.loads++ })

Source

sync3 test

sync/atomic provides lock-free atomic operations on integers — cheaper than

Show hint

Increment without a lock using an atomic operation:

atomic.AddInt64(&hits, 1)

Source