Go by Example: sync.RWMutex
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ref: sync.RWMutex Solving readers-writers problems Readers-writers problems occur when shared piece of data needs to be accessed by multiple threads. |
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package main |
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import ( "fmt" "math/rand" "strings" "sync" "time" ) |
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func init() { rand.Seed(time.Now().Unix()) } |
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func sleep() { time.Sleep(time.Duration(rand.Intn(100)) * time.Millisecond) } |
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func reader(c chan int, m *sync.RWMutex, wg *sync.WaitGroup) { sleep() m.RLock() // 1) acquire Read lock c <- 1 // 2) add acquired lock count sleep() // 3) do something after acquiring lock c <- -1 // 4) reduce acquired lock count m.RUnlock() wg.Done() } |
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func writer(c chan int, m *sync.RWMutex, wg *sync.WaitGroup) { sleep() m.Lock() // 1) acquire Write/Exclusive lock c <- 1 sleep() c <- -1 m.Unlock() wg.Done() } |
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const READER_COUNT = 10 const WRITER_COUNT = 3 |
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func main() { var m sync.RWMutex var rs, ws int readerCh := make(chan int) writerCh := make(chan int) |
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print out the lock count result |
go func() {
for {
select {
case n := <-readerCh:
rs += n
case n := <-writerCh:
ws += n
}
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simulate concurrent lock acquired count |
fmt.Printf("%s%s\n", strings.Repeat("R", rs),
strings.Repeat("W", ws))
}
}()
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wg := sync.WaitGroup{} for i := 0; i < 10; i++ { wg.Add(1) go reader(readerCh, &m, &wg) } for i := 0; i < 3; i++ { wg.Add(1) go writer(writerCh, &m, &wg) } wg.Wait() } |
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New line is printed each time set of goroutines executing critical section changes. It’s visible that RWMutex allows for either 1) at least one reader or 2) exactly one writer. |
go run rwmutex.go
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W R RR RRR RRRR RRRRR RRRR RRR RRRR RRR RR R W R RR RRR RRRR RRR RR R W |
Next example: sync.singleflight.