| // +build OMIT |
| |
| package main |
| |
| import ( |
| "fmt" |
| "sync" |
| "time" |
| ) |
| |
| // SafeCounter is safe to use concurrently. |
| type SafeCounter struct { |
| v map[string]int |
| mux sync.Mutex |
| } |
| |
| // Inc increments the counter for the given key. |
| func (c *SafeCounter) Inc(key string) { |
| c.mux.Lock() |
| // Lock so only one goroutine at a time can access the map c.v. |
| c.v[key]++ |
| c.mux.Unlock() |
| } |
| |
| // Value returns the current value of the counter for the given key. |
| func (c *SafeCounter) Value(key string) int { |
| c.mux.Lock() |
| // Lock so only one goroutine at a time can access the map c.v. |
| defer c.mux.Unlock() |
| return c.v[key] |
| } |
| |
| func main() { |
| c := SafeCounter{v: make(map[string]int)} |
| for i := 0; i < 1000; i++ { |
| go c.Inc("somekey") |
| } |
| |
| time.Sleep(time.Second) |
| fmt.Println(c.Value("somekey")) |
| } |