github.com/a4a881d4/docker@v1.9.0-rc2/graph/mutex.go (about)

     1  package graph
     2  
     3  import "sync"
     4  
     5  // imageMutex provides a lock per image id to protect shared resources in the
     6  // graph. This is only used with registration but should be used when
     7  // manipulating the layer store.
     8  type imageMutex struct {
     9  	mus map[string]*sync.Mutex // mutexes by image id.
    10  	mu  sync.Mutex             // protects lock map
    11  
    12  	// NOTE(stevvooe): The map above will grow to the size of all images ever
    13  	// registered during a daemon run. To free these resources, we must
    14  	// deallocate after unlock. Doing this safely is non-trivial in the face
    15  	// of a very minor leak.
    16  }
    17  
    18  // Lock the provided id.
    19  func (im *imageMutex) Lock(id string) {
    20  	im.getImageLock(id).Lock()
    21  }
    22  
    23  // Unlock the provided id.
    24  func (im *imageMutex) Unlock(id string) {
    25  	im.getImageLock(id).Unlock()
    26  }
    27  
    28  // getImageLock returns the mutex for the given id. This method will never
    29  // return nil.
    30  func (im *imageMutex) getImageLock(id string) *sync.Mutex {
    31  	im.mu.Lock()
    32  	defer im.mu.Unlock()
    33  
    34  	if im.mus == nil { // lazy
    35  		im.mus = make(map[string]*sync.Mutex)
    36  	}
    37  
    38  	mu, ok := im.mus[id]
    39  	if !ok {
    40  		mu = new(sync.Mutex)
    41  		im.mus[id] = mu
    42  	}
    43  
    44  	return mu
    45  }