55 lines
949 B
Go
55 lines
949 B
Go
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package main
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import (
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"fmt"
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"sync"
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)
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// START OMIT
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// SafeCounter is safe to use concurrently.
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type SafeCounter struct {
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v map[string]int
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mux sync.RWMutex
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}
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// Inc increments the counter for the given key.
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func (c *SafeCounter) Inc(key string) {
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c.mux.Lock()
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// Lock so only one goroutine at a time can access the map.
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defer c.mux.Unlock()
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c.v[key]++
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}
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// Value returns the current value of the counter for the given key.
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func (c *SafeCounter) Value(key string) int {
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c.mux.RLock()
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// Many readers can get this lock at once, but Lock() takes priority.
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defer c.mux.RUnlock()
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return c.v[key]
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}
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//END OMIT
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func main() {
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c := &SafeCounter{v: make(map[string]int)}
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s := sync.WaitGroup{}
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s.Add(3)
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go func() {
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c.Inc("key")
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fmt.Println(c.Value("key"))
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s.Done()
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}()
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go func() {
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c.Inc("key")
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fmt.Println(c.Value("key"))
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s.Done()
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}()
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go func() {
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c.Inc("key")
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fmt.Println(c.Value("key"))
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s.Done()
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}()
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s.Wait()
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}
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