golang仅在作者进行更改时才阻止读者

Question

I have one writer goroutine and multiple reader goroutines. I want to block readers when writer is changing data.

package main

data []int

func main() {
    m := sync.Mutex{}

    for i := 0; i< 10; i++ {
        go func reader() {
            for {
                m.Lock()
                myData := data
                m.Unlock()
                read_from_data(myData)
            }
        }()
    }

    go func writer() {
        for {
            newData := new_data()
            m.Lock()
            data = newData
            m.Unlock()
            time.Sleep(1 * time.Seconds)
        }
    }
}

How can i do this without readers blocking each other?

Answer 1

This is what sync.RWMutex is for.

It has 2 different lock methods: RWMutex.Lock() for writers, and RWMutex.RLock() for readers. (And there are 2 different unlock methods, matching the different lock methods: RWMutex.Unlock() and RWMutex.RUnlock().)

RWMutex allows multiple readers, or 1 writer. If a writer obtained the lock, no readers are allowed until the writer unlocks (also, no other writers allowed). If a reader obtains the read-lock, any other readers are allowed (but not a writer, not until all readers unlock).

m := sync.RWMutex{}

for i := 0; i < 10; i++ {
    go func() { // reader
        for {
            m.RLock()
            myData := data
            m.RUnlock()
            read_from_data(myData)
        }
    }()
}

go func() { // writer
    for {
        newData := new_data()
        m.Lock()
        data = newData
        m.Unlock()
        time.Sleep(1 * time.Seconds)
    }
}