Simplified memfs locking.

samples/memfs/inode.go

@@ -22,11 +22,12 @@ import (
 
 	"github.com/jacobsa/fuse/fuseops"
 	"github.com/jacobsa/fuse/fuseutil"
-	"github.com/jacobsa/syncutil"
 	"github.com/jacobsa/timeutil"
 )
 
 // Common attributes for files and directories.
+//
+// External synchronization is required.
 type inode struct {
 	/////////////////////////
 	// Dependencies
@@ -38,8 +39,6 @@ type inode struct {
 	// Mutable state
 	/////////////////////////
 
-	mu syncutil.InvariantMutex
-
 	// The current attributes of this inode.
 	//
 	// INVARIANT: attrs.Mode &^ (os.ModePerm|os.ModeDir|os.ModeSymlink) == 0
@@ -93,11 +92,10 @@ func newInode(
 		attrs: attrs,
 	}
 
-	in.mu = syncutil.NewInvariantMutex(in.checkInvariants)
 	return
 }
 
-func (in *inode) checkInvariants() {
+func (in *inode) CheckInvariants() {
 	// INVARIANT: attrs.Mode &^ (os.ModePerm|os.ModeDir|os.ModeSymlink) == 0
 	if !(in.attrs.Mode&^(os.ModePerm|os.ModeDir|os.ModeSymlink) == 0) {
 		panic(fmt.Sprintf("Unexpected mode: %v", in.attrs.Mode))
@@ -153,25 +151,21 @@ func (in *inode) checkInvariants() {
 	return
 }
 
-// LOCKS_REQUIRED(in.mu)
 func (in *inode) isDir() bool {
 	return in.attrs.Mode&os.ModeDir != 0
 }
 
-// LOCKS_REQUIRED(in.mu)
 func (in *inode) isSymlink() bool {
 	return in.attrs.Mode&os.ModeSymlink != 0
 }
 
-// LOCKS_REQUIRED(in.mu)
 func (in *inode) isFile() bool {
 	return !(in.isDir() || in.isSymlink())
 }
 
 // Return the index of the child within in.entries, if it exists.
 //
-// REQUIRES: in.dir
-// LOCKS_REQUIRED(in.mu)
+// REQUIRES: in.isDir()
 func (in *inode) findChild(name string) (i int, ok bool) {
 	if !in.isDir() {
 		panic("findChild called on non-directory.")
@@ -195,7 +189,6 @@ func (in *inode) findChild(name string) (i int, ok bool) {
 // Return the number of children of the directory.
 //
 // REQUIRES: in.isDir()
-// LOCKS_REQUIRED(in.mu)
 func (in *inode) Len() (n int) {
 	for _, e := range in.entries {
 		if e.Type != fuseutil.DT_Unknown {
@@ -209,7 +202,6 @@ func (in *inode) Len() (n int) {
 // Find an entry for the given child name and return its inode ID.
 //
 // REQUIRES: in.isDir()
-// LOCKS_REQUIRED(in.mu)
 func (in *inode) LookUpChild(name string) (id fuseops.InodeID, ok bool) {
 	index, ok := in.findChild(name)
 	if ok {
@@ -223,7 +215,6 @@ func (in *inode) LookUpChild(name string) (id fuseops.InodeID, ok bool) {
 //
 // REQUIRES: in.isDir()
 // REQUIRES: dt != fuseutil.DT_Unknown
-// LOCKS_REQUIRED(in.mu)
 func (in *inode) AddChild(
 	id fuseops.InodeID,
 	name string,
@@ -263,7 +254,6 @@ func (in *inode) AddChild(
 //
 // REQUIRES: in.isDir()
 // REQUIRES: An entry for the given name exists.
-// LOCKS_REQUIRED(in.mu)
 func (in *inode) RemoveChild(name string) {
 	// Update the modification time.
 	in.attrs.Mtime = in.clock.Now()
@@ -284,7 +274,6 @@ func (in *inode) RemoveChild(name string) {
 // Serve a ReadDir request.
 //
 // REQUIRES: in.isDir()
-// LOCKS_REQUIRED(in.mu)
 func (in *inode) ReadDir(offset int, size int) (data []byte, err error) {
 	if !in.isDir() {
 		panic("ReadDir called on non-directory.")
@@ -313,7 +302,6 @@ func (in *inode) ReadDir(offset int, size int) (data []byte, err error) {
 // Read from the file's contents. See documentation for ioutil.ReaderAt.
 //
 // REQUIRES: in.isFile()
-// LOCKS_REQUIRED(in.mu)
 func (in *inode) ReadAt(p []byte, off int64) (n int, err error) {
 	if !in.isFile() {
 		panic("ReadAt called on non-file.")
@@ -337,7 +325,6 @@ func (in *inode) ReadAt(p []byte, off int64) (n int, err error) {
 // Write to the file's contents. See documentation for ioutil.WriterAt.
 //
 // REQUIRES: in.isFile()
-// LOCKS_REQUIRED(in.mu)
 func (in *inode) WriteAt(p []byte, off int64) (n int, err error) {
 	if !in.isFile() {
 		panic("WriteAt called on non-file.")
@@ -366,8 +353,6 @@ func (in *inode) WriteAt(p []byte, off int64) (n int, err error) {
 }
 
 // Update attributes from non-nil parameters.
-//
-// LOCKS_REQUIRED(in.mu)
 func (in *inode) SetAttributes(
 	size *uint64,
 	mode *os.FileMode,

samples/memfs/memfs.go

@@ -40,13 +40,13 @@ type memFS struct {
 	// Mutable state
 	/////////////////////////
 
-	// When acquiring this lock, the caller must hold no inode locks.
 	mu syncutil.InvariantMutex
 
 	// The collection of live inodes, indexed by ID. IDs of free inodes that may
 	// be re-used have nil entries. No ID less than fuseops.RootInodeID is ever
 	// used.
 	//
+	// INVARIANT: For each inode in, in.CheckInvariants() does not panic.
 	// INVARIANT: len(inodes) > fuseops.RootInodeID
 	// INVARIANT: For all i < fuseops.RootInodeID, inodes[i] == nil
 	// INVARIANT: inodes[fuseops.RootInodeID] != nil
@@ -132,33 +132,32 @@ func (fs *memFS) checkInvariants() {
 			panic(fmt.Sprintf("Unexected free inode ID: %v", id))
 		}
 	}
+
+	// INVARIANT: For each inode in, in.CheckInvariants() does not panic.
+	for _, in := range fs.inodes {
+		in.CheckInvariants()
+	}
 }
 
-// Find the given inode and return it with its lock held. Panic if it doesn't
-// exist.
+// Find the given inode. Panic if it doesn't exist.
 //
 // LOCKS_REQUIRED(fs.mu)
-// LOCK_FUNCTION(inode.mu)
 func (fs *memFS) getInodeOrDie(id fuseops.InodeID) (inode *inode) {
 	inode = fs.inodes[id]
 	if inode == nil {
 		panic(fmt.Sprintf("Unknown inode: %v", id))
 	}
 
-	inode.mu.Lock()
 	return
 }
 
-// Allocate a new inode, assigning it an ID that is not in use. Return it with
-// its lock held.
+// Allocate a new inode, assigning it an ID that is not in use.
 //
-// EXCLUSIVE_LOCKS_REQUIRED(fs.mu)
-// EXCLUSIVE_LOCK_FUNCTION(inode.mu)
+// LOCKS_REQUIRED(fs.mu)
 func (fs *memFS) allocateInode(
 	attrs fuseops.InodeAttributes) (id fuseops.InodeID, inode *inode) {
-	// Create and lock the inode.
+	// Create the inode.
 	inode = newInode(fs.clock, attrs)
-	inode.mu.Lock()
 
 	// Re-use a free ID if possible. Otherwise mint a new one.
 	numFree := len(fs.freeInodes)
@@ -174,7 +173,7 @@ func (fs *memFS) allocateInode(
 	return
 }
 
-// EXCLUSIVE_LOCKS_REQUIRED(fs.mu)
+// LOCKS_REQUIRED(fs.mu)
 func (fs *memFS) deallocateInode(id fuseops.InodeID) {
 	fs.freeInodes = append(fs.freeInodes, id)
 	fs.inodes[id] = nil
@@ -191,7 +190,6 @@ func (fs *memFS) LookUpInode(
 
 	// Grab the parent directory.
 	inode := fs.getInodeOrDie(op.Parent)
-	defer inode.mu.Unlock()
 
 	// Does the directory have an entry with the given name?
 	childID, ok := inode.LookUpChild(op.Name)
@@ -202,7 +200,6 @@ func (fs *memFS) LookUpInode(
 
 	// Grab the child.
 	child := fs.getInodeOrDie(childID)
-	defer child.mu.Unlock()
 
 	// Fill in the response.
 	op.Entry.Child = childID
@@ -223,7 +220,6 @@ func (fs *memFS) GetInodeAttributes(
 
 	// Grab the inode.
 	inode := fs.getInodeOrDie(op.Inode)
-	defer inode.mu.Unlock()
 
 	// Fill in the response.
 	op.Attributes = inode.attrs
@@ -242,7 +238,6 @@ func (fs *memFS) SetInodeAttributes(
 
 	// Grab the inode.
 	inode := fs.getInodeOrDie(op.Inode)
-	defer inode.mu.Unlock()
 
 	// Handle the request.
 	inode.SetAttributes(op.Size, op.Mode, op.Mtime)
@@ -264,7 +259,6 @@ func (fs *memFS) MkDir(
 
 	// Grab the parent, which we will update shortly.
 	parent := fs.getInodeOrDie(op.Parent)
-	defer parent.mu.Unlock()
 
 	// Ensure that the name doesn't already exist, so we don't wind up with a
 	// duplicate.
@@ -285,7 +279,6 @@ func (fs *memFS) MkDir(
 
 	// Allocate a child.
 	childID, child := fs.allocateInode(childAttrs)
-	defer child.mu.Unlock()
 
 	// Add an entry in the parent.
 	parent.AddChild(childID, op.Name, fuseutil.DT_Directory)
@@ -309,7 +302,6 @@ func (fs *memFS) CreateFile(
 
 	// Grab the parent, which we will update shortly.
 	parent := fs.getInodeOrDie(op.Parent)
-	defer parent.mu.Unlock()
 
 	// Ensure that the name doesn't already exist, so we don't wind up with a
 	// duplicate.
@@ -335,7 +327,6 @@ func (fs *memFS) CreateFile(
 
 	// Allocate a child.
 	childID, child := fs.allocateInode(childAttrs)
-	defer child.mu.Unlock()
 
 	// Add an entry in the parent.
 	parent.AddChild(childID, op.Name, fuseutil.DT_File)
@@ -361,7 +352,6 @@ func (fs *memFS) CreateSymlink(
 
 	// Grab the parent, which we will update shortly.
 	parent := fs.getInodeOrDie(op.Parent)
-	defer parent.mu.Unlock()
 
 	// Ensure that the name doesn't already exist, so we don't wind up with a
 	// duplicate.
@@ -387,7 +377,6 @@ func (fs *memFS) CreateSymlink(
 
 	// Allocate a child.
 	childID, child := fs.allocateInode(childAttrs)
-	defer child.mu.Unlock()
 
 	// Set up its target.
 	child.target = op.Target
@@ -414,7 +403,6 @@ func (fs *memFS) RmDir(
 
 	// Grab the parent, which we will update shortly.
 	parent := fs.getInodeOrDie(op.Parent)
-	defer parent.mu.Unlock()
 
 	// Find the child within the parent.
 	childID, ok := parent.LookUpChild(op.Name)
@@ -425,7 +413,6 @@ func (fs *memFS) RmDir(
 
 	// Grab the child.
 	child := fs.getInodeOrDie(childID)
-	defer child.mu.Unlock()
 
 	// Make sure the child is empty.
 	if child.Len() != 0 {
@@ -449,7 +436,6 @@ func (fs *memFS) Unlink(
 
 	// Grab the parent, which we will update shortly.
 	parent := fs.getInodeOrDie(op.Parent)
-	defer parent.mu.Unlock()
 
 	// Find the child within the parent.
 	childID, ok := parent.LookUpChild(op.Name)
@@ -460,7 +446,6 @@ func (fs *memFS) Unlink(
 
 	// Grab the child.
 	child := fs.getInodeOrDie(childID)
-	defer child.mu.Unlock()
 
 	// Remove the entry within the parent.
 	parent.RemoveChild(op.Name)
@@ -480,7 +465,6 @@ func (fs *memFS) OpenDir(
 	// inode that doesn't exist, something screwed up earlier (a lookup, a
 	// cache invalidation, etc.).
 	inode := fs.getInodeOrDie(op.Inode)
-	defer inode.mu.Unlock()
 
 	if !inode.isDir() {
 		panic("Found non-dir.")
@@ -496,7 +480,6 @@ func (fs *memFS) ReadDir(
 
 	// Grab the directory.
 	inode := fs.getInodeOrDie(op.Inode)
-	defer inode.mu.Unlock()
 
 	// Serve the request.
 	op.Data, err = inode.ReadDir(int(op.Offset), op.Size)
@@ -517,7 +500,6 @@ func (fs *memFS) OpenFile(
 	// inode that doesn't exist, something screwed up earlier (a lookup, a
 	// cache invalidation, etc.).
 	inode := fs.getInodeOrDie(op.Inode)
-	defer inode.mu.Unlock()
 
 	if !inode.isFile() {
 		panic("Found non-file.")
@@ -533,7 +515,6 @@ func (fs *memFS) ReadFile(
 
 	// Find the inode in question.
 	inode := fs.getInodeOrDie(op.Inode)
-	defer inode.mu.Unlock()
 
 	// Serve the request.
 	op.Data = make([]byte, op.Size)
@@ -555,7 +536,6 @@ func (fs *memFS) WriteFile(
 
 	// Find the inode in question.
 	inode := fs.getInodeOrDie(op.Inode)
-	defer inode.mu.Unlock()
 
 	// Serve the request.
 	_, err = inode.WriteAt(op.Data, op.Offset)
@@ -570,7 +550,6 @@ func (fs *memFS) ReadSymlink(
 
 	// Find the inode in question.
 	inode := fs.getInodeOrDie(op.Inode)
-	defer inode.mu.Unlock()
 
 	// Serve the request.
 	op.Target = inode.target