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// Copyright 2015 The Vanadium 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 store
import (
// ResourceNode is a node in a dependency graph. This graph is used to ensure
// that when a resource is freed, downstream resources are also freed. For
// example, closing a store closes all downstream transactions, snapshots and
// streams.
type ResourceNode struct {
mu sync.Mutex
parent *ResourceNode
children map[*ResourceNode]func()
// NewResourceNode creates a new isolated node in the dependency graph.
func NewResourceNode() *ResourceNode {
return &ResourceNode{
children: make(map[*ResourceNode]func()),
// AddChild adds a parent-child relation between this node and the provided
// node. The provided function is called to close the child when this node is
// closed.
func (r *ResourceNode) AddChild(node *ResourceNode, closefn func()) {
if r.children == nil {
panic("already closed")
node.parent = r
r.children[node] = closefn
// removeChild removes the parent-child relation between this node and the
// provided node, enabling Go's garbage collector to free the resources
// associated with the child node if there are no more references to it.
func (r *ResourceNode) removeChild(node *ResourceNode) {
if r.children == nil {
// Already closed.
delete(r.children, node)
// Close closes this node and detaches it from its parent. All of this node's
// children are closed using close functions provided to AddChild.
func (r *ResourceNode) Close() {
if r.parent != nil {
// If there is a node V with parent P and we decide to explicitly close V,
// then we need to remove V from P's children list so that we don't close
// V again when P is closed.
r.parent = nil
// Copy the children map to a local variable so that the removeChild step
// executed from children won't affect the map while we iterate through it.
children := r.children
r.children = nil
for _, closefn := range children {