go/src/cmd/go/internal/lockedfile/mutex.go

type Mutex …

// MutexAt returns a new Mutex with Path set to the given non-empty path.
func MutexAt(path string) *Mutex { … }

func (mu *Mutex) String() string { … }

// Lock attempts to lock the Mutex.
//
// If successful, Lock returns a non-nil unlock function: it is provided as a
// return-value instead of a separate method to remind the caller to check the
// accompanying error. (See https://golang.org/issue/20803.)
func (mu *Mutex) Lock() (unlock func(), err error) { … }