moby--moby/daemon/graphdriver/counter.go

package graphdriver

import (
	"sync"

	"github.com/docker/docker/pkg/mount"
)

type minfo struct {
	check bool
	count int
}

// RefCounter is a generic counter for use by graphdriver Get/Put calls
type RefCounter struct {
	counts map[string]*minfo
	mu     sync.Mutex
}

// NewRefCounter returns a new RefCounter
func NewRefCounter() *RefCounter {
	return &RefCounter{counts: make(map[string]*minfo)}
}

// Increment increaes the ref count for the given id and returns the current count
func (c *RefCounter) Increment(path string) int {
	c.mu.Lock()
	m := c.counts[path]
	if m == nil {
		m = &minfo{check: true}
		c.counts[path] = m
	}
	// if we are checking this path for the first time check to make sure
	// if it was already mounted on the system and make sure we have a correct ref
	// count if it is mounted as it is in use.
	if !m.check {
		m.check = true
		mntd, _ := mount.Mounted(path)
		if mntd {
			m.count++
		}
	}
	m.count++
	c.mu.Unlock()
	return m.count
}

// Decrement decreases the ref count for the given id and returns the current count
func (c *RefCounter) Decrement(path string) int {
	c.mu.Lock()
	m := c.counts[path]
	if m == nil {
		m = &minfo{check: true}
		c.counts[path] = m
	}
	// if we are checking this path for the first time check to make sure
	// if it was already mounted on the system and make sure we have a correct ref
	// count if it is mounted as it is in use.
	if !m.check {
		m.check = true
		mntd, _ := mount.Mounted(path)
		if mntd {
			m.count++
		}
	}
	m.count--
	c.mu.Unlock()
	return m.count
}