go同步锁 sync mutex

package main
import (
  "fmt"
  "sync"
  "time"
)
// SafeCounter is safe to use concurrently.
type SafeCounter struct {
  mu sync.Mutex
  v  map[string]int
}
// Inc increments the counter for the given key.
func (c *SafeCounter) Inc(key string) {
  c.mu.Lock()
  // Lock so only one goroutine at a time can access the map c.v.
  c.v[key]++
  c.mu.Unlock()
}
// Value returns the current value of the counter for the given key.
func (c *SafeCounter) Value(key string) int {
  c.mu.Lock()
  // Lock so only one goroutine at a time can access the map c.v.
  defer c.mu.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"))
}