Factor DirCache from drive into its own module
This commit is contained in:
Nick Craig-Wood
@@ -0,0 +1,236 @@
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// dircache provides a simple cache for caching directory to path lookups
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package dircache
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import (
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"fmt"
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"log"
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"strings"
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"sync"
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)
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// DirCache caches paths to directory IDs and vice versa
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type DirCache struct {
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cacheLock sync.RWMutex
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cache map[string]string
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invCache map[string]string
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fs DirCacher // Interface to find and make stuff
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trueRootID string // ID of the absolute root
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findDirLock sync.Mutex // Protect findDir from concurrent use
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root string // the path we are working on
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rootID string // ID of the root directory
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findRootLock sync.Mutex // Protect findRoot from concurrent use
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foundRoot bool // Whether we have found the root or not
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}
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// DirCache describes an interface for doing the low level directory work
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type DirCacher interface {
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FindLeaf(pathID, leaf string) (pathIDOut string, found bool, err error)
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CreateDir(pathID, leaf string) (newID string, err error)
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}
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// Make a new DirCache
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//
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// The cache is safe for concurrent use
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func New(root string, trueRootID string, fs DirCacher) *DirCache {
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d := &DirCache{
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trueRootID: trueRootID,
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root: root,
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fs: fs,
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}
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d.Flush()
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d.ResetRoot()
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return d
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}
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// Gets an ID given a path
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func (dc *DirCache) Get(path string) (id string, ok bool) {
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dc.cacheLock.RLock()
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id, ok = dc.cache[path]
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dc.cacheLock.RUnlock()
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return
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}
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// GetInv gets a path given an ID
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func (dc *DirCache) GetInv(path string) (id string, ok bool) {
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dc.cacheLock.RLock()
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id, ok = dc.invCache[path]
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dc.cacheLock.RUnlock()
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return
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}
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// Put a path, id into the map
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func (dc *DirCache) Put(path, id string) {
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dc.cacheLock.Lock()
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dc.cache[path] = id
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dc.invCache[id] = path
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dc.cacheLock.Unlock()
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}
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// Flush the map of all data
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func (dc *DirCache) Flush() {
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dc.cacheLock.Lock()
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dc.cache = make(map[string]string)
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dc.invCache = make(map[string]string)
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dc.cacheLock.Unlock()
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}
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// Splits a path into directory, leaf
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//
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// Path shouldn't start or end with a /
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//
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// If there are no slashes then directory will be "" and leaf = path
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func SplitPath(path string) (directory, leaf string) {
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lastSlash := strings.LastIndex(path, "/")
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if lastSlash >= 0 {
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directory = path[:lastSlash]
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leaf = path[lastSlash+1:]
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} else {
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directory = ""
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leaf = path
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}
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return
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}
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// Finds the directory passed in returning the directory ID starting from pathID
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//
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// Path shouldn't start or end with a /
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//
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// If create is set it will make the directory if not found
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//
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// Algorithm:
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// Look in the cache for the path, if found return the pathID
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// If not found strip the last path off the path and recurse
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// Now have a parent directory id, so look in the parent for self and return it
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func (dc *DirCache) FindDir(path string, create bool) (pathID string, err error) {
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pathID = dc._findDirInCache(path)
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if pathID != "" {
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return
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}
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dc.findDirLock.Lock()
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defer dc.findDirLock.Unlock()
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return dc._findDir(path, create)
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}
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// Look for the root and in the cache - safe to call without the findDirLock
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func (dc *DirCache) _findDirInCache(path string) string {
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// fmt.Println("Finding",path,"create",create,"cache",cache)
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// If it is the root, then return it
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if path == "" {
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// fmt.Println("Root")
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return dc.rootID
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}
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// If it is in the cache then return it
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pathID, ok := dc.Get(path)
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if ok {
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// fmt.Println("Cache hit on", path)
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return pathID
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}
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return ""
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}
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// Unlocked findDir - must have findDirLock
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func (dc *DirCache) _findDir(path string, create bool) (pathID string, err error) {
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pathID = dc._findDirInCache(path)
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if pathID != "" {
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return pathID, nil
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}
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// Split the path into directory, leaf
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directory, leaf := SplitPath(path)
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// Recurse and find pathID for parent directory
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parentPathID, err := dc._findDir(directory, create)
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if err != nil {
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return "", err
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}
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// Find the leaf in parentPathID
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pathID, found, err := dc.fs.FindLeaf(parentPathID, leaf)
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if err != nil {
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return "", err
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}
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// If not found create the directory if required or return an error
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if !found {
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if create {
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pathID, err = dc.fs.CreateDir(parentPathID, leaf)
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if err != nil {
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return "", fmt.Errorf("Failed to make directory: %v", err)
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}
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} else {
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return "", fmt.Errorf("Couldn't find directory: %q", path)
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}
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}
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// Store the leaf directory in the cache
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dc.Put(path, pathID)
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// fmt.Println("Dir", path, "is", pathID)
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return pathID, nil
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}
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// FindPath finds the leaf and directoryID from a path
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//
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// If create is set parent directories will be created if they don't exist
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func (dc *DirCache) FindPath(path string, create bool) (leaf, directoryID string, err error) {
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directory, leaf := SplitPath(path)
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directoryID, err = dc.FindDir(directory, create)
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if err != nil {
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if create {
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err = fmt.Errorf("Couldn't find or make directory %q: %s", directory, err)
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} else {
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err = fmt.Errorf("Couldn't find directory %q: %s", directory, err)
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}
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}
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return
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}
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// Finds the root directory if not already found
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//
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// Resets the root directory
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//
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// If create is set it will make the directory if not found
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func (dc *DirCache) FindRoot(create bool) error {
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dc.findRootLock.Lock()
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defer dc.findRootLock.Unlock()
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if dc.foundRoot {
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return nil
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}
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rootID, err := dc.FindDir(dc.root, create)
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if err != nil {
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return err
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}
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dc.rootID = rootID
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dc.Flush()
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// Put the root directory in
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dc.Put("", dc.rootID)
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dc.foundRoot = true
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return nil
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}
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// RootID returns the ID of the root directory
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//
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// This should be called after FindRoot
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func (dc *DirCache) RootID() string {
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if dc.rootID == "" {
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log.Fatalf("Internal Error: RootID() called before FindRoot")
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}
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return dc.rootID
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}
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// Resets the root directory to the absolute root and clears the DirCache
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func (dc *DirCache) ResetRoot() {
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dc.findRootLock.Lock()
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defer dc.findRootLock.Unlock()
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dc.foundRoot = false
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dc.Flush()
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// Put the true root in
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dc.rootID = dc.trueRootID
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// Put the root directory in
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dc.Put("", dc.rootID)
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}
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