cache: factor fs cache into lib/cache

fs/cache/cache.go

@@ -2,93 +2,39 @@
 package cache
 
 import (
-	"sync"
-	"time"
-
 	"github.com/rclone/rclone/fs"
+	"github.com/rclone/rclone/lib/cache"
 )
 
 var (
-	fsCacheMu           sync.Mutex
-	fsCache             = map[string]*cacheEntry{}
-	fsNewFs             = fs.NewFs // for tests
-	expireRunning       = false
-	cacheExpireDuration = 300 * time.Second // expire the cache entry when it is older than this
-	cacheExpireInterval = 60 * time.Second  // interval to run the cache expire
+	c = cache.New()
 )
 
-type cacheEntry struct {
-	f        fs.Fs     // cached f
-	err      error     // nil or fs.ErrorIsFile
-	fsString string    // remote string
-	lastUsed time.Time // time used for expiry
+// GetFn gets a fs.Fs named fsString either from the cache or creates
+// it afresh with the create function
+func GetFn(fsString string, create func(fsString string) (fs.Fs, error)) (f fs.Fs, err error) {
+	value, err := c.Get(fsString, func(fsString string) (value interface{}, ok bool, error error) {
+		f, err := create(fsString)
+		ok = err == nil || err == fs.ErrorIsFile
+		return f, ok, err
+	})
+	if err != nil {
+		return nil, err
+	}
+	return value.(fs.Fs), nil
 }
 
 // Get gets a fs.Fs named fsString either from the cache or creates it afresh
 func Get(fsString string) (f fs.Fs, err error) {
-	fsCacheMu.Lock()
-	entry, ok := fsCache[fsString]
-	if !ok {
-		fsCacheMu.Unlock() // Unlock in case Get is called recursively
-		f, err = fsNewFs(fsString)
-		if err != nil && err != fs.ErrorIsFile {
-			return f, err
-		}
-		entry = &cacheEntry{
-			f:        f,
-			fsString: fsString,
-			err:      err,
-		}
-		fsCacheMu.Lock()
-		fsCache[fsString] = entry
-	}
-	defer fsCacheMu.Unlock()
-	entry.lastUsed = time.Now()
-	if !expireRunning {
-		time.AfterFunc(cacheExpireInterval, cacheExpire)
-		expireRunning = true
-	}
-	return entry.f, entry.err
+	return GetFn(fsString, fs.NewFs)
 }
 
 // Put puts an fs.Fs named fsString into the cache
 func Put(fsString string, f fs.Fs) {
-	fsCacheMu.Lock()
-	defer fsCacheMu.Unlock()
-	fsCache[fsString] = &cacheEntry{
-		f:        f,
-		fsString: fsString,
-		lastUsed: time.Now(),
-	}
-	if !expireRunning {
-		time.AfterFunc(cacheExpireInterval, cacheExpire)
-		expireRunning = true
-	}
-}
-
-// cacheExpire expires any entries that haven't been used recently
-func cacheExpire() {
-	fsCacheMu.Lock()
-	defer fsCacheMu.Unlock()
-	now := time.Now()
-	for fsString, entry := range fsCache {
-		if now.Sub(entry.lastUsed) > cacheExpireDuration {
-			delete(fsCache, fsString)
-		}
-	}
-	if len(fsCache) != 0 {
-		time.AfterFunc(cacheExpireInterval, cacheExpire)
-		expireRunning = true
-	} else {
-		expireRunning = false
-	}
+	c.Put(fsString, f)
 }
 
 // Clear removes everything from the cahce
 func Clear() {
-	fsCacheMu.Lock()
-	for k := range fsCache {
-		delete(fsCache, k)
-	}
-	fsCacheMu.Unlock()
+	c.Clear()
 }

fs/cache/cache_test.go

@@ -4,7 +4,6 @@ import (
 	"errors"
 	"fmt"
 	"testing"
-	"time"
 
 	"github.com/rclone/rclone/fs"
 	"github.com/rclone/rclone/fstest/mockfs"
@@ -17,10 +16,9 @@ var (
 	errSentinel = errors.New("an error")
 )
 
-func mockNewFs(t *testing.T) func() {
+func mockNewFs(t *testing.T) (func(), func(path string) (fs.Fs, error)) {
 	called = 0
-	oldFsNewFs := fsNewFs
-	fsNewFs = func(path string) (fs.Fs, error) {
+	create := func(path string) (fs.Fs, error) {
 		assert.Equal(t, 0, called)
 		called++
 		switch path {
@@ -33,115 +31,74 @@ func mockNewFs(t *testing.T) func() {
 		}
 		panic(fmt.Sprintf("Unknown path %q", path))
 	}
-	return func() {
-		fsNewFs = oldFsNewFs
-		fsCacheMu.Lock()
-		fsCache = map[string]*cacheEntry{}
-		expireRunning = false
-		fsCacheMu.Unlock()
+	cleanup := func() {
+		c.Clear()
 	}
+	return cleanup, create
 }
 
 func TestGet(t *testing.T) {
-	defer mockNewFs(t)()
+	cleanup, create := mockNewFs(t)
+	defer cleanup()
 
-	assert.Equal(t, 0, len(fsCache))
+	assert.Equal(t, 0, c.Entries())
 
-	f, err := Get("/")
+	f, err := GetFn("/", create)
 	require.NoError(t, err)
 
-	assert.Equal(t, 1, len(fsCache))
+	assert.Equal(t, 1, c.Entries())
 
-	f2, err := Get("/")
+	f2, err := GetFn("/", create)
 	require.NoError(t, err)
 
 	assert.Equal(t, f, f2)
 }
 
 func TestGetFile(t *testing.T) {
-	defer mockNewFs(t)()
+	cleanup, create := mockNewFs(t)
+	defer cleanup()
 
-	assert.Equal(t, 0, len(fsCache))
+	assert.Equal(t, 0, c.Entries())
 
-	f, err := Get("/file.txt")
+	f, err := GetFn("/file.txt", create)
 	require.Equal(t, fs.ErrorIsFile, err)
 
-	assert.Equal(t, 1, len(fsCache))
+	assert.Equal(t, 1, c.Entries())
 
-	f2, err := Get("/file.txt")
+	f2, err := GetFn("/file.txt", create)
 	require.Equal(t, fs.ErrorIsFile, err)
 
 	assert.Equal(t, f, f2)
 }
 
 func TestGetError(t *testing.T) {
-	defer mockNewFs(t)()
+	cleanup, create := mockNewFs(t)
+	defer cleanup()
 
-	assert.Equal(t, 0, len(fsCache))
+	assert.Equal(t, 0, c.Entries())
 
-	f, err := Get("/error")
+	f, err := GetFn("/error", create)
 	require.Equal(t, errSentinel, err)
 	require.Equal(t, nil, f)
 
-	assert.Equal(t, 0, len(fsCache))
+	assert.Equal(t, 0, c.Entries())
 }
 
 func TestPut(t *testing.T) {
-	defer mockNewFs(t)()
+	cleanup, create := mockNewFs(t)
+	defer cleanup()
 
 	f := mockfs.NewFs("mock", "mock")
 
-	assert.Equal(t, 0, len(fsCache))
+	assert.Equal(t, 0, c.Entries())
 
 	Put("/alien", f)
 
-	assert.Equal(t, 1, len(fsCache))
+	assert.Equal(t, 1, c.Entries())
 
-	fNew, err := Get("/alien")
+	fNew, err := GetFn("/alien", create)
 	require.NoError(t, err)
 	require.Equal(t, f, fNew)
 
-	assert.Equal(t, 1, len(fsCache))
-}
-
-func TestCacheExpire(t *testing.T) {
-	defer mockNewFs(t)()
-
-	cacheExpireInterval = time.Millisecond
-	assert.Equal(t, false, expireRunning)
-
-	_, err := Get("/")
-	require.NoError(t, err)
-
-	fsCacheMu.Lock()
-	entry := fsCache["/"]
-
-	assert.Equal(t, 1, len(fsCache))
-	fsCacheMu.Unlock()
-	cacheExpire()
-	fsCacheMu.Lock()
-	assert.Equal(t, 1, len(fsCache))
-	entry.lastUsed = time.Now().Add(-cacheExpireDuration - 60*time.Second)
-	assert.Equal(t, true, expireRunning)
-	fsCacheMu.Unlock()
-	time.Sleep(10 * time.Millisecond)
-	fsCacheMu.Lock()
-	assert.Equal(t, false, expireRunning)
-	assert.Equal(t, 0, len(fsCache))
-	fsCacheMu.Unlock()
-}
-
-func TestClear(t *testing.T) {
-	defer mockNewFs(t)()
-
-	assert.Equal(t, 0, len(fsCache))
-
-	_, err := Get("/")
-	require.NoError(t, err)
-
-	assert.Equal(t, 1, len(fsCache))
-
-	Clear()
-
-	assert.Equal(t, 0, len(fsCache))
+	assert.Equal(t, 1, c.Entries())
 }

lib/cache/cache.go

@@ -0,0 +1,134 @@
+// Package cache implements a simple cache where the entries are
+// expired after a given time (5 minutes of disuse by default).
+package cache
+
+import (
+	"sync"
+	"time"
+)
+
+// Cache holds values indexed by string, but expired after a given (5
+// minutes by default).
+type Cache struct {
+	mu             sync.Mutex
+	cache          map[string]*cacheEntry
+	expireRunning  bool
+	expireDuration time.Duration // expire the cache entry when it is older than this
+	expireInterval time.Duration // interval to run the cache expire
+}
+
+// New creates a new cache with the default expire duration and interval
+func New() *Cache {
+	return &Cache{
+		cache:          map[string]*cacheEntry{},
+		expireRunning:  false,
+		expireDuration: 300 * time.Second,
+		expireInterval: 60 * time.Second,
+	}
+}
+
+// cacheEntry is stored in the cache
+type cacheEntry struct {
+	value    interface{} // cached item
+	err      error       // creation error
+	key      string      // key
+	lastUsed time.Time   // time used for expiry
+}
+
+// CreateFunc is called to create new values.  If the create function
+// returns an error it will be cached if ok is true, otherwise the
+// error will just be returned, allowing negative caching if required.
+type CreateFunc func(key string) (value interface{}, ok bool, error error)
+
+// used marks an entry as accessed now and kicks the expire timer off
+// should be called with the lock held
+func (c *Cache) used(entry *cacheEntry) {
+	entry.lastUsed = time.Now()
+	if !c.expireRunning {
+		time.AfterFunc(c.expireInterval, c.cacheExpire)
+		c.expireRunning = true
+	}
+}
+
+// Get gets a value named key either from the cache or creates it
+// afresh with the create function.
+func (c *Cache) Get(key string, create CreateFunc) (value interface{}, err error) {
+	c.mu.Lock()
+	entry, ok := c.cache[key]
+	if !ok {
+		c.mu.Unlock() // Unlock in case Get is called recursively
+		value, ok, err = create(key)
+		if err != nil && !ok {
+			return value, err
+		}
+		entry = &cacheEntry{
+			value: value,
+			key:   key,
+			err:   err,
+		}
+		c.mu.Lock()
+		c.cache[key] = entry
+	}
+	defer c.mu.Unlock()
+	c.used(entry)
+	return entry.value, entry.err
+}
+
+// Put puts an value named key into the cache
+func (c *Cache) Put(key string, value interface{}) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	entry := &cacheEntry{
+		value: value,
+		key:   key,
+	}
+	c.used(entry)
+	c.cache[key] = entry
+}
+
+// GetMaybe returns the key and true if found, nil and false if not
+func (c *Cache) GetMaybe(key string) (value interface{}, found bool) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	entry, found := c.cache[key]
+	if !found {
+		return nil, found
+	}
+	c.used(entry)
+	return entry.value, found
+}
+
+// cacheExpire expires any entries that haven't been used recently
+func (c *Cache) cacheExpire() {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	now := time.Now()
+	for key, entry := range c.cache {
+		if now.Sub(entry.lastUsed) > c.expireDuration {
+			delete(c.cache, key)
+		}
+	}
+	if len(c.cache) != 0 {
+		time.AfterFunc(c.expireInterval, c.cacheExpire)
+		c.expireRunning = true
+	} else {
+		c.expireRunning = false
+	}
+}
+
+// Clear removes everything from the cahce
+func (c *Cache) Clear() {
+	c.mu.Lock()
+	for k := range c.cache {
+		delete(c.cache, k)
+	}
+	c.mu.Unlock()
+}
+
+// Entries returns the number of entries in the cache
+func (c *Cache) Entries() int {
+	c.mu.Lock()
+	entries := len(c.cache)
+	c.mu.Unlock()
+	return entries
+}

lib/cache/cache_test.go

@@ -0,0 +1,174 @@
+package cache
+
+import (
+	"errors"
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+var (
+	called      = 0
+	errSentinel = errors.New("an error")
+	errCached   = errors.New("a cached error")
+)
+
+func setup(t *testing.T) (*Cache, CreateFunc) {
+	called = 0
+	create := func(path string) (interface{}, bool, error) {
+		assert.Equal(t, 0, called)
+		called++
+		switch path {
+		case "/":
+			return "/", true, nil
+		case "/file.txt":
+			return "/file.txt", true, errCached
+		case "/error":
+			return nil, false, errSentinel
+		}
+		panic(fmt.Sprintf("Unknown path %q", path))
+	}
+	c := New()
+	return c, create
+}
+
+func TestGet(t *testing.T) {
+	c, create := setup(t)
+
+	assert.Equal(t, 0, len(c.cache))
+
+	f, err := c.Get("/", create)
+	require.NoError(t, err)
+
+	assert.Equal(t, 1, len(c.cache))
+
+	f2, err := c.Get("/", create)
+	require.NoError(t, err)
+
+	assert.Equal(t, f, f2)
+}
+
+func TestGetFile(t *testing.T) {
+	c, create := setup(t)
+
+	assert.Equal(t, 0, len(c.cache))
+
+	f, err := c.Get("/file.txt", create)
+	require.Equal(t, errCached, err)
+
+	assert.Equal(t, 1, len(c.cache))
+
+	f2, err := c.Get("/file.txt", create)
+	require.Equal(t, errCached, err)
+
+	assert.Equal(t, f, f2)
+}
+
+func TestGetError(t *testing.T) {
+	c, create := setup(t)
+
+	assert.Equal(t, 0, len(c.cache))
+
+	f, err := c.Get("/error", create)
+	require.Equal(t, errSentinel, err)
+	require.Equal(t, nil, f)
+
+	assert.Equal(t, 0, len(c.cache))
+}
+
+func TestPut(t *testing.T) {
+	c, create := setup(t)
+
+	assert.Equal(t, 0, len(c.cache))
+
+	c.Put("/alien", "slime")
+
+	assert.Equal(t, 1, len(c.cache))
+
+	fNew, err := c.Get("/alien", create)
+	require.NoError(t, err)
+	require.Equal(t, "slime", fNew)
+
+	assert.Equal(t, 1, len(c.cache))
+}
+
+func TestCacheExpire(t *testing.T) {
+	c, create := setup(t)
+
+	c.expireInterval = time.Millisecond
+	assert.Equal(t, false, c.expireRunning)
+
+	_, err := c.Get("/", create)
+	require.NoError(t, err)
+
+	c.mu.Lock()
+	entry := c.cache["/"]
+
+	assert.Equal(t, 1, len(c.cache))
+	c.mu.Unlock()
+	c.cacheExpire()
+	c.mu.Lock()
+	assert.Equal(t, 1, len(c.cache))
+	entry.lastUsed = time.Now().Add(-c.expireDuration - 60*time.Second)
+	assert.Equal(t, true, c.expireRunning)
+	c.mu.Unlock()
+	time.Sleep(10 * time.Millisecond)
+	c.mu.Lock()
+	assert.Equal(t, false, c.expireRunning)
+	assert.Equal(t, 0, len(c.cache))
+	c.mu.Unlock()
+}
+
+func TestClear(t *testing.T) {
+	c, create := setup(t)
+
+	assert.Equal(t, 0, len(c.cache))
+
+	_, err := c.Get("/", create)
+	require.NoError(t, err)
+
+	assert.Equal(t, 1, len(c.cache))
+
+	c.Clear()
+
+	assert.Equal(t, 0, len(c.cache))
+}
+
+func TestEntries(t *testing.T) {
+	c, create := setup(t)
+
+	assert.Equal(t, 0, c.Entries())
+
+	_, err := c.Get("/", create)
+	require.NoError(t, err)
+
+	assert.Equal(t, 1, c.Entries())
+
+	c.Clear()
+
+	assert.Equal(t, 0, c.Entries())
+}
+
+func TestGetMaybe(t *testing.T) {
+	c, create := setup(t)
+
+	value, found := c.GetMaybe("/")
+	assert.Equal(t, false, found)
+	assert.Nil(t, value)
+
+	f, err := c.Get("/", create)
+	require.NoError(t, err)
+
+	value, found = c.GetMaybe("/")
+	assert.Equal(t, true, found)
+	assert.Equal(t, f, value)
+
+	c.Clear()
+
+	value, found = c.GetMaybe("/")
+	assert.Equal(t, false, found)
+	assert.Nil(t, value)
+}