cache: set timeout to 24 hour - FIXME DO NOT MERGE

Before this fix, if several Get requests were submitted very quickly,
this could run the item create function multiple times due to the
unlock of the mutex in the creation code.

This fixes the problem by having a mutex in each cache entry which is
held when the item is being created.

backend/drive/drive.go

@@ -207,7 +207,7 @@ func init() {
 			}
 			err = configTeamDrive(ctx, opt, m, name)
 			if err != nil {
-				log.Fatalf("Failed to configure Shared Drive: %v", err)
+				log.Fatalf("Failed to configure team drive: %v", err)
 			}
 		},
 		Options: append(driveOAuthOptions(), []fs.Option{{
@@ -247,7 +247,7 @@ a non root folder as its starting point.
 			Advanced: true,
 		}, {
 			Name:     "team_drive",
-			Help:     "ID of the Shared Drive (Team Drive)",
+			Help:     "ID of the Team Drive",
 			Hide:     fs.OptionHideConfigurator,
 			Advanced: true,
 		}, {
@@ -666,7 +666,7 @@ func (f *Fs) shouldRetry(err error) (bool, error) {
 				fs.Errorf(f, "Received download limit error: %v", err)
 				return false, fserrors.FatalError(err)
 			} else if f.opt.StopOnUploadLimit && reason == "teamDriveFileLimitExceeded" {
-				fs.Errorf(f, "Received Shared Drive file limit error: %v", err)
+				fs.Errorf(f, "Received team drive file limit error: %v", err)
 				return false, fserrors.FatalError(err)
 			}
 		}
@@ -955,24 +955,24 @@ func configTeamDrive(ctx context.Context, opt *Options, m configmap.Mapper, name
 		return nil
 	}
 	if opt.TeamDriveID == "" {
-		fmt.Printf("Configure this as a Shared Drive (Team Drive)?\n")
+		fmt.Printf("Configure this as a team drive?\n")
 	} else {
-		fmt.Printf("Change current Shared Drive (Team Drive) ID %q?\n", opt.TeamDriveID)
+		fmt.Printf("Change current team drive ID %q?\n", opt.TeamDriveID)
 	}
 	if !config.Confirm(false) {
 		return nil
 	}
 	f, err := newFs(ctx, name, "", m)
 	if err != nil {
-		return errors.Wrap(err, "failed to make Fs to list Shared Drives")
+		return errors.Wrap(err, "failed to make Fs to list teamdrives")
 	}
-	fmt.Printf("Fetching Shared Drive list...\n")
+	fmt.Printf("Fetching team drive list...\n")
 	teamDrives, err := f.listTeamDrives(ctx)
 	if err != nil {
 		return err
 	}
 	if len(teamDrives) == 0 {
-		fmt.Printf("No Shared Drives found in your account")
+		fmt.Printf("No team drives found in your account")
 		return nil
 	}
 	var driveIDs, driveNames []string
@@ -980,7 +980,7 @@ func configTeamDrive(ctx context.Context, opt *Options, m configmap.Mapper, name
 		driveIDs = append(driveIDs, teamDrive.Id)
 		driveNames = append(driveNames, teamDrive.Name)
 	}
-	driveID := config.Choose("Enter a Shared Drive ID", driveIDs, driveNames, true)
+	driveID := config.Choose("Enter a Team Drive ID", driveIDs, driveNames, true)
 	m.Set("team_drive", driveID)
 	m.Set("root_folder_id", "")
 	opt.TeamDriveID = driveID
@@ -2475,9 +2475,9 @@ func (f *Fs) teamDriveOK(ctx context.Context) (err error) {
 		return f.shouldRetry(err)
 	})
 	if err != nil {
-		return errors.Wrap(err, "failed to get Shared Drive info")
+		return errors.Wrap(err, "failed to get Team/Shared Drive info")
 	}
-	fs.Debugf(f, "read info from Shared Drive %q", td.Name)
+	fs.Debugf(f, "read info from team drive %q", td.Name)
 	return err
 }
 
@@ -2963,7 +2963,7 @@ func (f *Fs) listTeamDrives(ctx context.Context) (drives []*drive.TeamDrive, err
 			return defaultFs.shouldRetry(err)
 		})
 		if err != nil {
-			return drives, errors.Wrap(err, "listing Team Drives failed")
+			return drives, errors.Wrap(err, "listing team drives failed")
 		}
 		drives = append(drives, teamDrives.TeamDrives...)
 		if teamDrives.NextPageToken == "" {
@@ -3131,8 +3131,8 @@ authenticated with "drive2:" can't read files from "drive:".
 	},
 }, {
 	Name:  "drives",
-	Short: "List the Shared Drives available to this account",
-	Long: `This command lists the Shared Drives (Team Drives) available to this
+	Short: "List the shared drives available to this account",
+	Long: `This command lists the shared drives (teamdrives) available to this
 account.
 
 Usage:

cmd/cmount/fs.go

@@ -5,7 +5,6 @@
 package cmount
 
 import (
-	"context"
 	"io"
 	"os"
 	"path"
@@ -19,11 +18,9 @@ import (
 	"github.com/rclone/rclone/fs"
 	"github.com/rclone/rclone/fs/log"
 	"github.com/rclone/rclone/vfs"
-	"golang.org/x/time/rate"
 )
 
 const fhUnset = ^uint64(0)
-const tpsBurst = 100
 
 // FS represents the top level filing system
 type FS struct {
@@ -32,31 +29,19 @@ type FS struct {
 	ready     chan (struct{})
 	mu        sync.Mutex // to protect the below
 	handles   []vfs.Handle
-	destroyed int32         // read/write with sync/atomic
-	tps       *rate.Limiter // for limiting number of transactions per second
+	destroyed int32 // read/write with sync/atomic
 }
 
 // NewFS makes a new FS
-func NewFS(VFS *vfs.VFS, opt *mountlib.Options) *FS {
+func NewFS(VFS *vfs.VFS) *FS {
 	fsys := &FS{
 		VFS:   VFS,
 		f:     VFS.Fs(),
 		ready: make(chan (struct{})),
 	}
-	if opt.TPSLimit > 0 {
-		fsys.tps = rate.NewLimiter(rate.Limit(opt.TPSLimit), tpsBurst)
-		fs.Infof(nil, "Starting mount transaction limiter: max %g transactions/s with burst %d", opt.TPSLimit, tpsBurst)
-	}
 	return fsys
 }
 
-// Limit the number of transactions per second
-func (fsys *FS) rateLimit() {
-	if fsys.tps != nil {
-		_ = fsys.tps.Wait(context.Background())
-	}
-}
-
 // Open a handle returning an integer file handle
 func (fsys *FS) openHandle(handle vfs.Handle) (fh uint64) {
 	fsys.mu.Lock()
@@ -210,7 +195,6 @@ func (fsys *FS) Destroy() {
 // Getattr reads the attributes for path
 func (fsys *FS) Getattr(path string, stat *fuse.Stat_t, fh uint64) (errc int) {
 	defer log.Trace(path, "fh=0x%X", fh)("errc=%v", &errc)
-	fsys.rateLimit()
 	node, _, errc := fsys.getNode(path, fh)
 	if errc == 0 {
 		errc = fsys.stat(node, stat)
@@ -221,7 +205,6 @@ func (fsys *FS) Getattr(path string, stat *fuse.Stat_t, fh uint64) (errc int) {
 // Opendir opens path as a directory
 func (fsys *FS) Opendir(path string) (errc int, fh uint64) {
 	defer log.Trace(path, "")("errc=%d, fh=0x%X", &errc, &fh)
-	fsys.rateLimit()
 	handle, err := fsys.VFS.OpenFile(path, os.O_RDONLY, 0777)
 	if err != nil {
 		return translateError(err), fhUnset
@@ -236,7 +219,6 @@ func (fsys *FS) Readdir(dirPath string,
 	fh uint64) (errc int) {
 	itemsRead := -1
 	defer log.Trace(dirPath, "ofst=%d, fh=0x%X", ofst, fh)("items=%d, errc=%d", &itemsRead, &errc)
-	fsys.rateLimit()
 
 	dir, errc := fsys.lookupDir(dirPath)
 	if errc != 0 {
@@ -288,14 +270,12 @@ func (fsys *FS) Readdir(dirPath string,
 // Releasedir finished reading the directory
 func (fsys *FS) Releasedir(path string, fh uint64) (errc int) {
 	defer log.Trace(path, "fh=0x%X", fh)("errc=%d", &errc)
-	fsys.rateLimit()
 	return fsys.closeHandle(fh)
 }
 
 // Statfs reads overall stats on the filesystem
 func (fsys *FS) Statfs(path string, stat *fuse.Statfs_t) (errc int) {
 	defer log.Trace(path, "")("stat=%+v, errc=%d", stat, &errc)
-	fsys.rateLimit()
 	const blockSize = 4096
 	total, _, free := fsys.VFS.Statfs()
 	stat.Blocks = uint64(total) / blockSize // Total data blocks in file system.
@@ -315,7 +295,6 @@ func (fsys *FS) Statfs(path string, stat *fuse.Statfs_t) (errc int) {
 // OpenEx opens a file
 func (fsys *FS) OpenEx(path string, fi *fuse.FileInfo_t) (errc int) {
 	defer log.Trace(path, "flags=0x%X", fi.Flags)("errc=%d, fh=0x%X", &errc, &fi.Fh)
-	fsys.rateLimit()
 	fi.Fh = fhUnset
 
 	// translate the fuse flags to os flags
@@ -346,7 +325,6 @@ func (fsys *FS) Open(path string, flags int) (errc int, fh uint64) {
 // CreateEx creates and opens a file.
 func (fsys *FS) CreateEx(filePath string, mode uint32, fi *fuse.FileInfo_t) (errc int) {
 	defer log.Trace(filePath, "flags=0x%X, mode=0%o", fi.Flags, mode)("errc=%d, fh=0x%X", &errc, &fi.Fh)
-	fsys.rateLimit()
 	fi.Fh = fhUnset
 	leaf, parentDir, errc := fsys.lookupParentDir(filePath)
 	if errc != 0 {
@@ -378,7 +356,6 @@ func (fsys *FS) Create(filePath string, flags int, mode uint32) (errc int, fh ui
 // Truncate truncates a file to size
 func (fsys *FS) Truncate(path string, size int64, fh uint64) (errc int) {
 	defer log.Trace(path, "size=%d, fh=0x%X", size, fh)("errc=%d", &errc)
-	fsys.rateLimit()
 	node, handle, errc := fsys.getNode(path, fh)
 	if errc != 0 {
 		return errc
@@ -398,7 +375,6 @@ func (fsys *FS) Truncate(path string, size int64, fh uint64) (errc int) {
 // Read data from file handle
 func (fsys *FS) Read(path string, buff []byte, ofst int64, fh uint64) (n int) {
 	defer log.Trace(path, "ofst=%d, fh=0x%X", ofst, fh)("n=%d", &n)
-	fsys.rateLimit()
 	handle, errc := fsys.getHandle(fh)
 	if errc != 0 {
 		return errc
@@ -414,7 +390,6 @@ func (fsys *FS) Read(path string, buff []byte, ofst int64, fh uint64) (n int) {
 // Write data to file handle
 func (fsys *FS) Write(path string, buff []byte, ofst int64, fh uint64) (n int) {
 	defer log.Trace(path, "ofst=%d, fh=0x%X", ofst, fh)("n=%d", &n)
-	fsys.rateLimit()
 	handle, errc := fsys.getHandle(fh)
 	if errc != 0 {
 		return errc
@@ -429,7 +404,6 @@ func (fsys *FS) Write(path string, buff []byte, ofst int64, fh uint64) (n int) {
 // Flush flushes an open file descriptor or path
 func (fsys *FS) Flush(path string, fh uint64) (errc int) {
 	defer log.Trace(path, "fh=0x%X", fh)("errc=%d", &errc)
-	fsys.rateLimit()
 	handle, errc := fsys.getHandle(fh)
 	if errc != 0 {
 		return errc
@@ -440,7 +414,6 @@ func (fsys *FS) Flush(path string, fh uint64) (errc int) {
 // Release closes the file if still open
 func (fsys *FS) Release(path string, fh uint64) (errc int) {
 	defer log.Trace(path, "fh=0x%X", fh)("errc=%d", &errc)
-	fsys.rateLimit()
 	handle, errc := fsys.getHandle(fh)
 	if errc != 0 {
 		return errc
@@ -452,7 +425,6 @@ func (fsys *FS) Release(path string, fh uint64) (errc int) {
 // Unlink removes a file.
 func (fsys *FS) Unlink(filePath string) (errc int) {
 	defer log.Trace(filePath, "")("errc=%d", &errc)
-	fsys.rateLimit()
 	leaf, parentDir, errc := fsys.lookupParentDir(filePath)
 	if errc != 0 {
 		return errc
@@ -463,7 +435,6 @@ func (fsys *FS) Unlink(filePath string) (errc int) {
 // Mkdir creates a directory.
 func (fsys *FS) Mkdir(dirPath string, mode uint32) (errc int) {
 	defer log.Trace(dirPath, "mode=0%o", mode)("errc=%d", &errc)
-	fsys.rateLimit()
 	leaf, parentDir, errc := fsys.lookupParentDir(dirPath)
 	if errc != 0 {
 		return errc
@@ -475,7 +446,6 @@ func (fsys *FS) Mkdir(dirPath string, mode uint32) (errc int) {
 // Rmdir removes a directory
 func (fsys *FS) Rmdir(dirPath string) (errc int) {
 	defer log.Trace(dirPath, "")("errc=%d", &errc)
-	fsys.rateLimit()
 	leaf, parentDir, errc := fsys.lookupParentDir(dirPath)
 	if errc != 0 {
 		return errc
@@ -486,7 +456,6 @@ func (fsys *FS) Rmdir(dirPath string) (errc int) {
 // Rename renames a file.
 func (fsys *FS) Rename(oldPath string, newPath string) (errc int) {
 	defer log.Trace(oldPath, "newPath=%q", newPath)("errc=%d", &errc)
-	fsys.rateLimit()
 	return translateError(fsys.VFS.Rename(oldPath, newPath))
 }
 
@@ -498,7 +467,6 @@ var invalidDateCutoff = time.Date(1601, 1, 2, 0, 0, 0, 0, time.UTC)
 // Utimens changes the access and modification times of a file.
 func (fsys *FS) Utimens(path string, tmsp []fuse.Timespec) (errc int) {
 	defer log.Trace(path, "tmsp=%+v", tmsp)("errc=%d", &errc)
-	fsys.rateLimit()
 	node, errc := fsys.lookupNode(path)
 	if errc != 0 {
 		return errc
@@ -519,14 +487,12 @@ func (fsys *FS) Utimens(path string, tmsp []fuse.Timespec) (errc int) {
 // Mknod creates a file node.
 func (fsys *FS) Mknod(path string, mode uint32, dev uint64) (errc int) {
 	defer log.Trace(path, "mode=0x%X, dev=0x%X", mode, dev)("errc=%d", &errc)
-	fsys.rateLimit()
 	return -fuse.ENOSYS
 }
 
 // Fsync synchronizes file contents.
 func (fsys *FS) Fsync(path string, datasync bool, fh uint64) (errc int) {
 	defer log.Trace(path, "datasync=%v, fh=0x%X", datasync, fh)("errc=%d", &errc)
-	fsys.rateLimit()
 	// This is a no-op for rclone
 	return 0
 }
@@ -534,28 +500,24 @@ func (fsys *FS) Fsync(path string, datasync bool, fh uint64) (errc int) {
 // Link creates a hard link to a file.
 func (fsys *FS) Link(oldpath string, newpath string) (errc int) {
 	defer log.Trace(oldpath, "newpath=%q", newpath)("errc=%d", &errc)
-	fsys.rateLimit()
 	return -fuse.ENOSYS
 }
 
 // Symlink creates a symbolic link.
 func (fsys *FS) Symlink(target string, newpath string) (errc int) {
 	defer log.Trace(target, "newpath=%q", newpath)("errc=%d", &errc)
-	fsys.rateLimit()
 	return -fuse.ENOSYS
 }
 
 // Readlink reads the target of a symbolic link.
 func (fsys *FS) Readlink(path string) (errc int, linkPath string) {
 	defer log.Trace(path, "")("linkPath=%q, errc=%d", &linkPath, &errc)
-	fsys.rateLimit()
 	return -fuse.ENOSYS, ""
 }
 
 // Chmod changes the permission bits of a file.
 func (fsys *FS) Chmod(path string, mode uint32) (errc int) {
 	defer log.Trace(path, "mode=0%o", mode)("errc=%d", &errc)
-	fsys.rateLimit()
 	// This is a no-op for rclone
 	return 0
 }
@@ -563,7 +525,6 @@ func (fsys *FS) Chmod(path string, mode uint32) (errc int) {
 // Chown changes the owner and group of a file.
 func (fsys *FS) Chown(path string, uid uint32, gid uint32) (errc int) {
 	defer log.Trace(path, "uid=%d, gid=%d", uid, gid)("errc=%d", &errc)
-	fsys.rateLimit()
 	// This is a no-op for rclone
 	return 0
 }
@@ -571,7 +532,6 @@ func (fsys *FS) Chown(path string, uid uint32, gid uint32) (errc int) {
 // Access checks file access permissions.
 func (fsys *FS) Access(path string, mask uint32) (errc int) {
 	defer log.Trace(path, "mask=0%o", mask)("errc=%d", &errc)
-	fsys.rateLimit()
 	// This is a no-op for rclone
 	return 0
 }
@@ -579,32 +539,27 @@ func (fsys *FS) Access(path string, mask uint32) (errc int) {
 // Fsyncdir synchronizes directory contents.
 func (fsys *FS) Fsyncdir(path string, datasync bool, fh uint64) (errc int) {
 	defer log.Trace(path, "datasync=%v, fh=0x%X", datasync, fh)("errc=%d", &errc)
-	fsys.rateLimit()
 	// This is a no-op for rclone
 	return 0
 }
 
 // Setxattr sets extended attributes.
 func (fsys *FS) Setxattr(path string, name string, value []byte, flags int) (errc int) {
-	fsys.rateLimit()
 	return -fuse.ENOSYS
 }
 
 // Getxattr gets extended attributes.
 func (fsys *FS) Getxattr(path string, name string) (errc int, value []byte) {
-	fsys.rateLimit()
 	return -fuse.ENOSYS, nil
 }
 
 // Removexattr removes extended attributes.
 func (fsys *FS) Removexattr(path string, name string) (errc int) {
-	fsys.rateLimit()
 	return -fuse.ENOSYS
 }
 
 // Listxattr lists extended attributes.
 func (fsys *FS) Listxattr(path string, fill func(name string) bool) (errc int) {
-	fsys.rateLimit()
 	return -fuse.ENOSYS
 }
 

cmd/cmount/mount.go

@@ -138,7 +138,7 @@ func mount(VFS *vfs.VFS, mountPath string, opt *mountlib.Options) (<-chan error,
 
 	// Create underlying FS
 	f := VFS.Fs()
-	fsys := NewFS(VFS, opt)
+	fsys := NewFS(VFS)
 	host := fuse.NewFileSystemHost(fsys)
 	host.SetCapReaddirPlus(true) // only works on Windows
 	host.SetCapCaseInsensitive(f.Features().CaseInsensitive)

cmd/mountlib/mount.go

@@ -45,7 +45,6 @@ type Options struct {
 	DaemonTimeout      time.Duration // OSXFUSE only
 	AsyncRead          bool
 	NetworkMode        bool // Windows only
-	TPSLimit           float64
 }
 
 // DefaultOpt is the default values for creating the mount
@@ -98,7 +97,6 @@ func AddFlags(flagSet *pflag.FlagSet) {
 	flags.BoolVarP(flagSet, &Opt.AsyncRead, "async-read", "", Opt.AsyncRead, "Use asynchronous reads. Not supported on Windows.")
 	flags.FVarP(flagSet, &Opt.MaxReadAhead, "max-read-ahead", "", "The number of bytes that can be prefetched for sequential reads. Not supported on Windows.")
 	flags.BoolVarP(flagSet, &Opt.WritebackCache, "write-back-cache", "", Opt.WritebackCache, "Makes kernel buffer writes before sending them to rclone. Without this, writethrough caching is used. Not supported on Windows.")
-	flags.Float64VarP(flagSet, &Opt.TPSLimit, "mount-tpslimit", "", 0, "Limit mount transactions per second to this. (0 is off).")
 	// Windows and OSX
 	flags.StringVarP(flagSet, &Opt.VolumeName, "volname", "", Opt.VolumeName, "Set the volume name. Supported on Windows and OSX only.")
 	// OSX only

docs/content/authors.md

@@ -456,4 +456,3 @@ put them back in again.` >}}
   * Nicolas Rueff <nicolas@rueff.fr>
   * Pau Rodriguez-Estivill <prodrigestivill@gmail.com>
   * Bob Pusateri <BobPusateri@users.noreply.github.com>
-  * Alex JOST <25005220+dimejo@users.noreply.github.com>

docs/content/drive.md

@@ -72,7 +72,7 @@ If your browser doesn't open automatically go to the following link: http://127.
 Log in and authorize rclone for access
 Waiting for code...
 Got code
-Configure this as a Shared Drive (Team Drive)?
+Configure this as a team drive?
 y) Yes
 n) No
 y/n> n
@@ -279,24 +279,23 @@ Note: in case you configured a specific root folder on gdrive and rclone is unab
         `rclone -v foo@example.com lsf gdrive:backup`
 
 
-### Shared drives (team drives) ###
+### Team drives ###
 
-If you want to configure the remote to point to a Google Shared Drive
-(previously known as Team Drives) then answer `y` to the question
-`Configure this as a Shared Drive (Team Drive)?`.
+If you want to configure the remote to point to a Google Team Drive
+then answer `y` to the question `Configure this as a team drive?`.
 
-This will fetch the list of Shared Drives from google and allow you to
-configure which one you want to use. You can also type in a Shared
-Drive ID if you prefer.
+This will fetch the list of Team Drives from google and allow you to
+configure which one you want to use.  You can also type in a team
+drive ID if you prefer.
 
 For example:
 
 ```
-Configure this as a Shared Drive (Team Drive)?
+Configure this as a team drive?
 y) Yes
 n) No
 y/n> y
-Fetching Shared Drive list...
+Fetching team drive list...
 Choose a number from below, or type in your own value
  1 / Rclone Test
    \ "xxxxxxxxxxxxxxxxxxxx"
@@ -304,7 +303,7 @@ Choose a number from below, or type in your own value
    \ "yyyyyyyyyyyyyyyyyyyy"
  3 / Rclone Test 3
    \ "zzzzzzzzzzzzzzzzzzzz"
-Enter a Shared Drive ID> 1
+Enter a Team Drive ID> 1
 --------------------
 [remote]
 client_id =
@@ -675,7 +674,7 @@ Needed only if you want use SA instead of interactive login.
 
 #### --drive-team-drive
 
-ID of the Shared Drive (Team Drive)
+ID of the Team Drive
 
 - Config:      team_drive
 - Env Var:     RCLONE_DRIVE_TEAM_DRIVE
@@ -1138,11 +1137,11 @@ Options:
 
 #### drives
 
-List the Shared Drives available to this account
+List the shared drives available to this account
 
     rclone backend drives remote: [options] [<arguments>+]
 
-This command lists the Shared Drives (Team Drives) available to this
+This command lists the shared drives (teamdrives) available to this
 account.
 
 Usage:

lib/cache/cache.go

@@ -22,15 +22,17 @@ func New() *Cache {
 	return &Cache{
 		cache:          map[string]*cacheEntry{},
 		expireRunning:  false,
-		expireDuration: 300 * time.Second,
+		expireDuration: 24 * time.Hour,
 		expireInterval: 60 * time.Second,
 	}
 }
 
 // cacheEntry is stored in the cache
 type cacheEntry struct {
+	createMu sync.Mutex  // held while creating the item
 	value    interface{} // cached item
 	err      error       // creation error
+	ok       bool        // true if entry is valid
 	key      string      // key
 	lastUsed time.Time   // time used for expiry
 	pinCount int         // non zero if the entry should not be removed
@@ -55,23 +57,27 @@ func (c *Cache) used(entry *cacheEntry) {
 // 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, found := c.cache[key]
+	if !found {
 		entry = &cacheEntry{
-			value: value,
-			key:   key,
-			err:   err,
+			key: key,
 		}
-		c.mu.Lock()
 		c.cache[key] = entry
 	}
-	defer c.mu.Unlock()
-	c.used(entry)
+	c.mu.Unlock()
+	// Only one racing Get will have found=false here
+	entry.createMu.Lock()
+	if !found {
+		entry.value, entry.ok, entry.err = create(key)
+	}
+	entry.createMu.Unlock()
+	c.mu.Lock()
+	if !found && !entry.ok {
+		delete(c.cache, key)
+	} else {
+		c.used(entry)
+	}
+	c.mu.Unlock()
 	return entry.value, entry.err
 }
 
@@ -102,6 +108,7 @@ func (c *Cache) Put(key string, value interface{}) {
 	entry := &cacheEntry{
 		value: value,
 		key:   key,
+		ok:    true,
 	}
 	c.used(entry)
 	c.cache[key] = entry
@@ -112,7 +119,7 @@ func (c *Cache) GetMaybe(key string) (value interface{}, found bool) {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	entry, found := c.cache[key]
-	if !found {
+	if !found || !entry.ok {
 		return nil, found
 	}
 	c.used(entry)

lib/cache/cache_test.go

@@ -3,6 +3,8 @@ package cache
 import (
 	"errors"
 	"fmt"
+	"sync"
+	"sync/atomic"
 	"testing"
 	"time"
 
@@ -11,7 +13,7 @@ import (
 )
 
 var (
-	called      = 0
+	called      = int32(0)
 	errSentinel = errors.New("an error")
 	errCached   = errors.New("a cached error")
 )
@@ -19,17 +21,19 @@ var (
 func setup(t *testing.T) (*Cache, CreateFunc) {
 	called = 0
 	create := func(path string) (interface{}, bool, error) {
-		assert.Equal(t, 0, called)
-		called++
+		newCalled := atomic.AddInt32(&called, 1)
+		assert.Equal(t, int32(1), newCalled)
 		switch path {
 		case "/":
+			time.Sleep(100 * time.Millisecond)
 			return "/", true, nil
 		case "/file.txt":
 			return "/file.txt", true, errCached
 		case "/error":
 			return nil, false, errSentinel
 		}
-		panic(fmt.Sprintf("Unknown path %q", path))
+		assert.Fail(t, fmt.Sprintf("Unknown path %q", path))
+		return nil, false, nil
 	}
 	c := New()
 	return c, create
@@ -51,6 +55,24 @@ func TestGet(t *testing.T) {
 	assert.Equal(t, f, f2)
 }
 
+func TestGetConcurrent(t *testing.T) {
+	c, create := setup(t)
+	assert.Equal(t, 0, len(c.cache))
+
+	var wg sync.WaitGroup
+	for i := 0; i < 100; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			_, err := c.Get("/", create)
+			require.NoError(t, err)
+		}()
+	}
+	wg.Wait()
+
+	assert.Equal(t, 1, len(c.cache))
+}
+
 func TestGetFile(t *testing.T) {
 	c, create := setup(t)