dep ensure

vendor/github.com/hanwen/go-fuse/fuse/nodefs/handle.go

@@ -0,0 +1,151 @@
+// Copyright 2016 the Go-FUSE Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package nodefs
+
+import (
+	"log"
+	"sync"
+)
+
+// HandleMap translates objects in Go space to 64-bit handles that can
+// be given out to -say- the linux kernel as NodeIds.
+//
+// The 32 bits version of this is a threadsafe wrapper around a map.
+//
+// To use it, include "handled" as first member of the structure
+// you wish to export.
+//
+// This structure is thread-safe.
+type handleMap interface {
+	// Register stores "obj" and returns a unique (NodeId, generation) tuple.
+	Register(obj *handled) (handle, generation uint64)
+	Count() int
+	// Decode retrieves a stored object from its 64-bit handle.
+	Decode(uint64) *handled
+	// Forget decrements the reference counter for "handle" by "count" and drops
+	// the object if the refcount reaches zero.
+	// Returns a boolean whether the object was dropped and the object itself.
+	Forget(handle uint64, count int) (bool, *handled)
+	// Handle gets the object's NodeId.
+	Handle(obj *handled) uint64
+	// Has checks if NodeId is stored.
+	Has(uint64) bool
+}
+
+type handled struct {
+	check  uint32
+	handle uint64
+	count  int
+}
+
+func (h *handled) verify() {
+	if h.count < 0 {
+		log.Panicf("negative lookup count %d", h.count)
+	}
+	if (h.count == 0) != (h.handle == 0) {
+		log.Panicf("registration mismatch: lookup %d id %d", h.count, h.handle)
+	}
+}
+
+const _ALREADY_MSG = "Object already has a handle"
+
+////////////////////////////////////////////////////////////////
+// portable version using 32 bit integers.
+
+type portableHandleMap struct {
+	sync.RWMutex
+	// The generation counter is incremented each time a NodeId is reused,
+	// hence the (NodeId, Generation) tuple is always unique.
+	generation uint64
+	// Number of currently used handles
+	used int
+	// Array of Go objects indexed by NodeId
+	handles []*handled
+	// Free slots in the "handles" array
+	freeIds []uint64
+}
+
+func newPortableHandleMap() *portableHandleMap {
+	return &portableHandleMap{
+		// Avoid handing out ID 0 and 1.
+		handles: []*handled{nil, nil},
+	}
+}
+
+func (m *portableHandleMap) Register(obj *handled) (handle, generation uint64) {
+	m.Lock()
+	if obj.count == 0 {
+		if obj.check != 0 {
+			panic(_ALREADY_MSG)
+		}
+
+		if len(m.freeIds) == 0 {
+			handle = uint64(len(m.handles))
+			m.handles = append(m.handles, obj)
+		} else {
+			handle = m.freeIds[len(m.freeIds)-1]
+			m.freeIds = m.freeIds[:len(m.freeIds)-1]
+			m.generation++
+			m.handles[handle] = obj
+		}
+		m.used++
+		obj.handle = handle
+	} else {
+		handle = obj.handle
+	}
+	obj.count++
+	generation = m.generation
+	m.Unlock()
+	return
+}
+
+func (m *portableHandleMap) Handle(obj *handled) (h uint64) {
+	m.RLock()
+	if obj.count == 0 {
+		h = 0
+	} else {
+		h = obj.handle
+	}
+	m.RUnlock()
+	return h
+}
+
+func (m *portableHandleMap) Count() int {
+	m.RLock()
+	c := m.used
+	m.RUnlock()
+	return c
+}
+
+func (m *portableHandleMap) Decode(h uint64) *handled {
+	m.RLock()
+	v := m.handles[h]
+	m.RUnlock()
+	return v
+}
+
+func (m *portableHandleMap) Forget(h uint64, count int) (forgotten bool, obj *handled) {
+	m.Lock()
+	obj = m.handles[h]
+	obj.count -= count
+	if obj.count < 0 {
+		log.Panicf("underflow: handle %d, count %d, object %d", h, count, obj.count)
+	} else if obj.count == 0 {
+		m.handles[h] = nil
+		m.freeIds = append(m.freeIds, h)
+		m.used--
+		forgotten = true
+		obj.handle = 0
+	}
+	m.Unlock()
+	return forgotten, obj
+}
+
+func (m *portableHandleMap) Has(h uint64) bool {
+	m.RLock()
+	ok := m.handles[h] != nil
+	m.RUnlock()
+	return ok
+}