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moby--moby/graph/mutex.go

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package graph
import "sync"
// imageMutex provides a lock per image id to protect shared resources in the
// graph. This is only used with registration but should be used when
// manipulating the layer store.
type imageMutex struct {
mus map[string]*sync.Mutex // mutexes by image id.
mu sync.Mutex // protects lock map
// NOTE(stevvooe): The map above will grow to the size of all images ever
// registered during a daemon run. To free these resources, we must
// deallocate after unlock. Doing this safely is non-trivial in the face
// of a very minor leak.
}
// Lock the provided id.
func (im *imageMutex) Lock(id string) {
im.getImageLock(id).Lock()
}
// Unlock the provided id.
func (im *imageMutex) Unlock(id string) {
im.getImageLock(id).Unlock()
}
// getImageLock returns the mutex for the given id. This method will never
// return nil.
func (im *imageMutex) getImageLock(id string) *sync.Mutex {
im.mu.Lock()
defer im.mu.Unlock()
if im.mus == nil { // lazy
im.mus = make(map[string]*sync.Mutex)
}
mu, ok := im.mus[id]
if !ok {
mu = new(sync.Mutex)
im.mus[id] = mu
}
return mu
}