与列表进行数据竞争。使用互斥体列出并发访问

Question

I'm getting a data race and I can't quite figure out why. Running my tests with the -race command I've narrowed it down to trying to access a list.List while reading from it, but my Mutexes don't seem to do anything.

I have a number of *list.Lists inside of an array like so:

type MyList struct {
    mutex sync.Mutex
    *list.List
}

type SomeObj struct {
    data string
}

var myListOfLists [10]MyList

I'm reading and writing from the list like so:

list := myListOfLists[someIndex]
list.mutex.Lock()
for e := list.Front(); e != nil; e = e.Next() {
        if (...) {
            list.MoveToFront(e)
        }
}
list.mutex.Unlock()

and in another goroutine also trying to read and build a full list to return

var fullCopy []*SomeObj
list := myListOfLists[someIndex]

list.mutex.Lock()
for e := list.Front(); e != nil; e = e.Next() {
        fullCopy = append(fullCopy, e.Value.(SomeObj))
}
list.mutex.Unlock()

Answer 1

The statement list := myListOfLists[someIndex] copies the array element to variable list . This copies the mutex, thus preventing the mutex from working. The go vet command reports this problem.

You can avoid the copy by using a pointer to the array element:

list := &myListOfLists[someIndex]

Another approach is to use an array of pointers to MyList . While you are at it, you might as well use a list value instead a list pointer in MyList :

type MyList struct {
    mutex sync.Mutex
    list.List
}

var myListOfLists [10]*MyList
for i := range myListOfLists {
   myListOfLists[i] = &MyList{}
}