Golang Once source code analysis

Sync. Once can implement a singleton mode to ensure sync. Once.do (f func ()) is executed only once and can initialize an instance singleton.

Sync for Golang 1.9. Once, the same as the Golang 1.10. Source code location: Sync\once.go.

Structural body

The once structure is defined as follows:

type Once struct {    m    Mutex    done uint32   // 初始值为0表示还未执行过，1表示已经执行过}

Do

func (o *Once) Do(f func()) {    // done==1表示已经执行过了，直接结束返回    if atomic.LoadUint32(&o.done) == 1 {        return    }    // 锁住对象，避免并发问题    o.m.Lock()    defer o.m.Unlock()    if o.done == 0 {        // 先将done设置为1，再执行f函数        defer atomic.StoreUint32(&o.done, 1)        f()    }}

It is important to note that the Execute F function is synchronous, which means there may be a blocking problem.