最小化地图上的锁定-而是尽快锁定单个项目

I want to minimize the lock held on a map of items that can be individually locked as soon as the relevant item has been retrieved.

That lead me to believe that

var Mymap struct {
    sync.Mutex
    m map[string]*Somestruct
}

type Somestruct struct {
    sync.Mutex
    Someval string
}

could be used like this:

Mymap.Lock()
if val, ok := Mymap.m.[needle]; ok {
    Mymap.m.[needle].Lock()
    Mymap.Unlock()
    // do something to this entry
    Mymap.m.[needle].Unlock()
}
Mymap.Unlock()

…but as I understand Unlock() on an already Unlocked is not a no-op:

panic: sync: unlock of unlocked mutex

As per https://groups.google.com/forum/#!topic/Golang-Nuts/GeHbpo6AtTc I see that there is no way to check that it is actually Unlocked.

Should I just keep the "Lock" state somewhere or is there a better way of doing it than this:

var unlocked bool

Mymap.Lock()
if val, ok := Mymap.m.[needle]; ok {
    Mymap.m.[needle].Lock()
    Mymap.Unlock()
    unlocked := true

    // do something to this entry
    Mymap.m.[needle].Unlock()
}

if !unlocked {
    Mymap.Unlock()
}

Mymap.Lock()
if val, ok := Mymap.m.[needle]; ok {
    Mymap.m.[needle].Lock()
    Mymap.Unlock()
    // do something to this entry
    Mymap.m.[needle].Unlock()
} else {
    Mymap.Unlock()
}