pgraph: Clean up pgraph module to get ready for clean lib status

The graph of dependencies in golang is a DAG, and as such doesn't allow cycles. Clean up this lib so that it eventually doesn't import our resources module or anything else which might want to import it. This patch makes adjacency private, and adds a generalized key store to the graph struct.
2017-05-13 11:47:34 -04:00
parent 4bb553e015
commit d11854f4e8
12 changed files with 263 additions and 206 deletions
--- a/examples/lib/libmgmt2.go
+++ b/examples/lib/libmgmt2.go
@@ -59,7 +59,10 @@ func (obj *MyGAPI) Graph() (*pgraph.Graph, error) {
 		return nil, fmt.Errorf("libmgmt: MyGAPI is not initialized")
 	}

-	g := pgraph.NewGraph(obj.Name)
+	g, err := pgraph.NewGraph(obj.Name)
+	if err != nil {
+		return nil, err
+	}
 	var vertex *pgraph.Vertex
 	for i := uint(0); i < obj.Count; i++ {
 		n := &resources.NoopRes{
--- a/examples/lib/libmgmt3.go
+++ b/examples/lib/libmgmt3.go
@@ -56,7 +56,10 @@ func (obj *MyGAPI) Graph() (*pgraph.Graph, error) {
 		return nil, fmt.Errorf("libmgmt: MyGAPI is not initialized")
 	}

-	g := pgraph.NewGraph(obj.Name)
+	g, err := pgraph.NewGraph(obj.Name)
+	if err != nil {
+		return nil, err
+	}

 	// FIXME: these are being specified temporarily until it's the default!
 	metaparams := resources.DefaultMetaParams
--- a/pgraph/actions.go
+++ b/pgraph/actions.go
@@ -87,7 +87,7 @@ func (g *Graph) Poke(v *Vertex) error {
 			wg.Add(1)
 			go func(nn *Vertex) error {
 				defer wg.Done()
-				//edge := g.Adjacency[v][nn] // lookup
+				//edge := g.adjacency[v][nn] // lookup
 				//notify := edge.Notify && edge.Refresh()
 				return nn.SendEvent(event.EventPoke, nil)
 			}(n)
--- a/pgraph/autogroup.go
+++ b/pgraph/autogroup.go
@@ -204,11 +204,11 @@ func (g *Graph) VertexMerge(v1, v2 *Vertex, vertexMergeFn func(*Vertex, *Vertex)
 	// methodology
 	// 1) edges between v1 and v2 are removed
 	//Loop:
-	for k1 := range g.Adjacency {
-		for k2 := range g.Adjacency[k1] {
+	for k1 := range g.adjacency {
+		for k2 := range g.adjacency[k1] {
 			// v1 -> v2 || v2 -> v1
 			if (k1 == v1 && k2 == v2) || (k1 == v2 && k2 == v1) {
-				delete(g.Adjacency[k1], k2) // delete map & edge
+				delete(g.adjacency[k1], k2) // delete map & edge
 				// NOTE: if we assume this is a DAG, then we can
 				// assume only v1 -> v2 OR v2 -> v1 exists, and
 				// we can break out of these loops immediately!
@@ -220,10 +220,10 @@ func (g *Graph) VertexMerge(v1, v2 *Vertex, vertexMergeFn func(*Vertex, *Vertex)

 	// 2) edges that point towards v2 from X now point to v1 from X (no dupes)
 	for _, x := range g.IncomingGraphVertices(v2) { // all to vertex v (??? -> v)
-		e := g.Adjacency[x][v2] // previous edge
+		e := g.adjacency[x][v2] // previous edge
 		r := g.Reachability(x, v1)
-		// merge e with ex := g.Adjacency[x][v1] if it exists!
-		if ex, exists := g.Adjacency[x][v1]; exists && edgeMergeFn != nil && len(r) == 0 {
+		// merge e with ex := g.adjacency[x][v1] if it exists!
+		if ex, exists := g.adjacency[x][v1]; exists && edgeMergeFn != nil && len(r) == 0 {
 			e = edgeMergeFn(e, ex)
 		}
 		if len(r) == 0 { // if not reachable, add it
@@ -236,21 +236,21 @@ func (g *Graph) VertexMerge(v1, v2 *Vertex, vertexMergeFn func(*Vertex, *Vertex)
 					continue
 				}
 				// this edge is from: prev, to: next
-				ex, _ := g.Adjacency[prev][next] // get
+				ex, _ := g.adjacency[prev][next] // get
 				ex = edgeMergeFn(ex, e)
-				g.Adjacency[prev][next] = ex // set
+				g.adjacency[prev][next] = ex // set
 				prev = next
 			}
 		}
-		delete(g.Adjacency[x], v2) // delete old edge
+		delete(g.adjacency[x], v2) // delete old edge
 	}

 	// 3) edges that point from v2 to X now point from v1 to X (no dupes)
 	for _, x := range g.OutgoingGraphVertices(v2) { // all from vertex v (v -> ???)
-		e := g.Adjacency[v2][x] // previous edge
+		e := g.adjacency[v2][x] // previous edge
 		r := g.Reachability(v1, x)
-		// merge e with ex := g.Adjacency[v1][x] if it exists!
-		if ex, exists := g.Adjacency[v1][x]; exists && edgeMergeFn != nil && len(r) == 0 {
+		// merge e with ex := g.adjacency[v1][x] if it exists!
+		if ex, exists := g.adjacency[v1][x]; exists && edgeMergeFn != nil && len(r) == 0 {
 			e = edgeMergeFn(e, ex)
 		}
 		if len(r) == 0 {
@@ -263,13 +263,13 @@ func (g *Graph) VertexMerge(v1, v2 *Vertex, vertexMergeFn func(*Vertex, *Vertex)
 					continue
 				}
 				// this edge is from: prev, to: next
-				ex, _ := g.Adjacency[prev][next]
+				ex, _ := g.adjacency[prev][next]
 				ex = edgeMergeFn(ex, e)
-				g.Adjacency[prev][next] = ex
+				g.adjacency[prev][next] = ex
 				prev = next
 			}
 		}
-		delete(g.Adjacency[v2], x)
+		delete(g.adjacency[v2], x)
 	}

 	// 4) merge and then remove the (now merged/grouped) vertex
--- a/pgraph/autogroup_test.go
+++ b/pgraph/autogroup_test.go
@@ -30,19 +30,19 @@ import (

 // empty graph
 func TestPgraphGrouping1(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
-	g2 := NewGraph("g2") // expected result
+	g1, _ := NewGraph("g1") // original graph
+	g2, _ := NewGraph("g2") // expected result
 	runGraphCmp(t, g1, g2)
 }

 // single vertex
 func TestPgraphGrouping2(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
-	{                    // grouping to limit variable scope
+	g1, _ := NewGraph("g1") // original graph
+	{                       // grouping to limit variable scope
 		a1 := NewVertex(NewNoopResTest("a1"))
 		g1.AddVertex(a1)
 	}
-	g2 := NewGraph("g2") // expected result
+	g2, _ := NewGraph("g2") // expected result
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		g2.AddVertex(a1)
@@ -52,13 +52,13 @@ func TestPgraphGrouping2(t *testing.T) {

 // two vertices
 func TestPgraphGrouping3(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
+	g1, _ := NewGraph("g1") // original graph
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		b1 := NewVertex(NewNoopResTest("b1"))
 		g1.AddVertex(a1, b1)
 	}
-	g2 := NewGraph("g2") // expected result
+	g2, _ := NewGraph("g2") // expected result
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		b1 := NewVertex(NewNoopResTest("b1"))
@@ -69,13 +69,13 @@ func TestPgraphGrouping3(t *testing.T) {

 // two vertices merge
 func TestPgraphGrouping4(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
+	g1, _ := NewGraph("g1") // original graph
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		a2 := NewVertex(NewNoopResTest("a2"))
 		g1.AddVertex(a1, a2)
 	}
-	g2 := NewGraph("g2") // expected result
+	g2, _ := NewGraph("g2") // expected result
 	{
 		a := NewVertex(NewNoopResTest("a1,a2"))
 		g2.AddVertex(a)
@@ -85,14 +85,14 @@ func TestPgraphGrouping4(t *testing.T) {

 // three vertices merge
 func TestPgraphGrouping5(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
+	g1, _ := NewGraph("g1") // original graph
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		a2 := NewVertex(NewNoopResTest("a2"))
 		a3 := NewVertex(NewNoopResTest("a3"))
 		g1.AddVertex(a1, a2, a3)
 	}
-	g2 := NewGraph("g2") // expected result
+	g2, _ := NewGraph("g2") // expected result
 	{
 		a := NewVertex(NewNoopResTest("a1,a2,a3"))
 		g2.AddVertex(a)
@@ -102,14 +102,14 @@ func TestPgraphGrouping5(t *testing.T) {

 // three vertices, two merge
 func TestPgraphGrouping6(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
+	g1, _ := NewGraph("g1") // original graph
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		a2 := NewVertex(NewNoopResTest("a2"))
 		b1 := NewVertex(NewNoopResTest("b1"))
 		g1.AddVertex(a1, a2, b1)
 	}
-	g2 := NewGraph("g2") // expected result
+	g2, _ := NewGraph("g2") // expected result
 	{
 		a := NewVertex(NewNoopResTest("a1,a2"))
 		b1 := NewVertex(NewNoopResTest("b1"))
@@ -120,7 +120,7 @@ func TestPgraphGrouping6(t *testing.T) {

 // four vertices, three merge
 func TestPgraphGrouping7(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
+	g1, _ := NewGraph("g1") // original graph
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		a2 := NewVertex(NewNoopResTest("a2"))
@@ -128,7 +128,7 @@ func TestPgraphGrouping7(t *testing.T) {
 		b1 := NewVertex(NewNoopResTest("b1"))
 		g1.AddVertex(a1, a2, a3, b1)
 	}
-	g2 := NewGraph("g2") // expected result
+	g2, _ := NewGraph("g2") // expected result
 	{
 		a := NewVertex(NewNoopResTest("a1,a2,a3"))
 		b1 := NewVertex(NewNoopResTest("b1"))
@@ -139,7 +139,7 @@ func TestPgraphGrouping7(t *testing.T) {

 // four vertices, two&two merge
 func TestPgraphGrouping8(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
+	g1, _ := NewGraph("g1") // original graph
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		a2 := NewVertex(NewNoopResTest("a2"))
@@ -147,7 +147,7 @@ func TestPgraphGrouping8(t *testing.T) {
 		b2 := NewVertex(NewNoopResTest("b2"))
 		g1.AddVertex(a1, a2, b1, b2)
 	}
-	g2 := NewGraph("g2") // expected result
+	g2, _ := NewGraph("g2") // expected result
 	{
 		a := NewVertex(NewNoopResTest("a1,a2"))
 		b := NewVertex(NewNoopResTest("b1,b2"))
@@ -158,7 +158,7 @@ func TestPgraphGrouping8(t *testing.T) {

 // five vertices, two&three merge
 func TestPgraphGrouping9(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
+	g1, _ := NewGraph("g1") // original graph
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		a2 := NewVertex(NewNoopResTest("a2"))
@@ -167,7 +167,7 @@ func TestPgraphGrouping9(t *testing.T) {
 		b3 := NewVertex(NewNoopResTest("b3"))
 		g1.AddVertex(a1, a2, b1, b2, b3)
 	}
-	g2 := NewGraph("g2") // expected result
+	g2, _ := NewGraph("g2") // expected result
 	{
 		a := NewVertex(NewNoopResTest("a1,a2"))
 		b := NewVertex(NewNoopResTest("b1,b2,b3"))
@@ -178,14 +178,14 @@ func TestPgraphGrouping9(t *testing.T) {

 // three unique vertices
 func TestPgraphGrouping10(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
+	g1, _ := NewGraph("g1") // original graph
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		b1 := NewVertex(NewNoopResTest("b1"))
 		c1 := NewVertex(NewNoopResTest("c1"))
 		g1.AddVertex(a1, b1, c1)
 	}
-	g2 := NewGraph("g2") // expected result
+	g2, _ := NewGraph("g2") // expected result
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		b1 := NewVertex(NewNoopResTest("b1"))
@@ -197,7 +197,7 @@ func TestPgraphGrouping10(t *testing.T) {

 // three unique vertices, two merge
 func TestPgraphGrouping11(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
+	g1, _ := NewGraph("g1") // original graph
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		b1 := NewVertex(NewNoopResTest("b1"))
@@ -205,7 +205,7 @@ func TestPgraphGrouping11(t *testing.T) {
 		c1 := NewVertex(NewNoopResTest("c1"))
 		g1.AddVertex(a1, b1, b2, c1)
 	}
-	g2 := NewGraph("g2") // expected result
+	g2, _ := NewGraph("g2") // expected result
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		b := NewVertex(NewNoopResTest("b1,b2"))
@@ -220,7 +220,7 @@ func TestPgraphGrouping11(t *testing.T) {
 //   \ /     >>>     |     (arrows point downwards)
 //    b              b
 func TestPgraphGrouping12(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
+	g1, _ := NewGraph("g1") // original graph
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		a2 := NewVertex(NewNoopResTest("a2"))
@@ -230,7 +230,7 @@ func TestPgraphGrouping12(t *testing.T) {
 		g1.AddEdge(a1, b1, e1)
 		g1.AddEdge(a2, b1, e2)
 	}
-	g2 := NewGraph("g2") // expected result
+	g2, _ := NewGraph("g2") // expected result
 	{
 		a := NewVertex(NewNoopResTest("a1,a2"))
 		b1 := NewVertex(NewNoopResTest("b1"))
@@ -245,7 +245,7 @@ func TestPgraphGrouping12(t *testing.T) {
 //   / \     >>>     |     (arrows point downwards)
 // a1   a2         a1,a2
 func TestPgraphGrouping13(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
+	g1, _ := NewGraph("g1") // original graph
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		a2 := NewVertex(NewNoopResTest("a2"))
@@ -255,7 +255,7 @@ func TestPgraphGrouping13(t *testing.T) {
 		g1.AddEdge(b1, a1, e1)
 		g1.AddEdge(b1, a2, e2)
 	}
-	g2 := NewGraph("g2") // expected result
+	g2, _ := NewGraph("g2") // expected result
 	{
 		a := NewVertex(NewNoopResTest("a1,a2"))
 		b1 := NewVertex(NewNoopResTest("b1"))
@@ -270,7 +270,7 @@ func TestPgraphGrouping13(t *testing.T) {
 //   \ | /     >>>       |      (arrows point downwards)
 //     b                 b
 func TestPgraphGrouping14(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
+	g1, _ := NewGraph("g1") // original graph
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		a2 := NewVertex(NewNoopResTest("a2"))
@@ -283,7 +283,7 @@ func TestPgraphGrouping14(t *testing.T) {
 		g1.AddEdge(a2, b1, e2)
 		g1.AddEdge(a3, b1, e3)
 	}
-	g2 := NewGraph("g2") // expected result
+	g2, _ := NewGraph("g2") // expected result
 	{
 		a := NewVertex(NewNoopResTest("a1,a2,a3"))
 		b1 := NewVertex(NewNoopResTest("b1"))
@@ -300,7 +300,7 @@ func TestPgraphGrouping14(t *testing.T) {
 //   \  /             |
 //    c1             c1
 func TestPgraphGrouping15(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
+	g1, _ := NewGraph("g1") // original graph
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		b1 := NewVertex(NewNoopResTest("b1"))
@@ -315,7 +315,7 @@ func TestPgraphGrouping15(t *testing.T) {
 		g1.AddEdge(b1, c1, e3)
 		g1.AddEdge(b2, c1, e4)
 	}
-	g2 := NewGraph("g2") // expected result
+	g2, _ := NewGraph("g2") // expected result
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		b := NewVertex(NewNoopResTest("b1,b2"))
@@ -337,7 +337,7 @@ func TestPgraphGrouping15(t *testing.T) {
 //  | /               |            | /
 // c1                c1           c1
 func TestPgraphGrouping16(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
+	g1, _ := NewGraph("g1") // original graph
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		a2 := NewVertex(NewNoopResTest("a2"))
@@ -350,7 +350,7 @@ func TestPgraphGrouping16(t *testing.T) {
 		g1.AddEdge(b1, c1, e2)
 		g1.AddEdge(a2, c1, e3)
 	}
-	g2 := NewGraph("g2") // expected result
+	g2, _ := NewGraph("g2") // expected result
 	{
 		a := NewVertex(NewNoopResTest("a1,a2"))
 		b1 := NewVertex(NewNoopResTest("b1"))
@@ -370,7 +370,7 @@ func TestPgraphGrouping16(t *testing.T) {
 //  | /               |
 // c1                c1
 func TestPgraphGrouping17(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
+	g1, _ := NewGraph("g1") // original graph
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		b1 := NewVertex(NewNoopResTest("b1"))
@@ -383,7 +383,7 @@ func TestPgraphGrouping17(t *testing.T) {
 		g1.AddEdge(b1, c1, e2)
 		g1.AddEdge(b2, c1, e3)
 	}
-	g2 := NewGraph("g2") // expected result
+	g2, _ := NewGraph("g2") // expected result
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		b := NewVertex(NewNoopResTest("b1,b2"))
@@ -404,7 +404,7 @@ func TestPgraphGrouping17(t *testing.T) {
 //     \ | /               |
 //      c1                c1
 func TestPgraphGrouping18(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
+	g1, _ := NewGraph("g1") // original graph
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		a2 := NewVertex(NewNoopResTest("a2"))
@@ -420,7 +420,7 @@ func TestPgraphGrouping18(t *testing.T) {
 		g1.AddEdge(a2, c1, e3)
 		g1.AddEdge(b2, c1, e4)
 	}
-	g2 := NewGraph("g2") // expected result
+	g2, _ := NewGraph("g2") // expected result
 	{
 		a := NewVertex(NewNoopResTest("a1,a2"))
 		b := NewVertex(NewNoopResTest("b1,b2"))
@@ -438,14 +438,14 @@ func TestPgraphGrouping18(t *testing.T) {
 //   \     >>>     \     (arrows point downwards)
 //    a2            a2
 func TestPgraphGroupingConnected0(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
+	g1, _ := NewGraph("g1") // original graph
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		a2 := NewVertex(NewNoopResTest("a2"))
 		e1 := NewEdge("e1")
 		g1.AddEdge(a1, a2, e1)
 	}
-	g2 := NewGraph("g2") // expected result ?
+	g2, _ := NewGraph("g2") // expected result ?
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		a2 := NewVertex(NewNoopResTest("a2"))
@@ -462,7 +462,7 @@ func TestPgraphGroupingConnected0(t *testing.T) {
 //     \               \
 //      a2              a2
 func TestPgraphGroupingConnected1(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
+	g1, _ := NewGraph("g1") // original graph
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		b := NewVertex(NewNoopResTest("b"))
@@ -472,7 +472,7 @@ func TestPgraphGroupingConnected1(t *testing.T) {
 		g1.AddEdge(a1, b, e1)
 		g1.AddEdge(b, a2, e2)
 	}
-	g2 := NewGraph("g2") // expected result ?
+	g2, _ := NewGraph("g2") // expected result ?
 	{
 		a1 := NewVertex(NewNoopResTest("a1"))
 		b := NewVertex(NewNoopResTest("b"))
--- a/pgraph/graphviz.go
+++ b/pgraph/graphviz.go
@@ -45,10 +45,10 @@ func (g *Graph) Graphviz() (out string) {
 	out += fmt.Sprintf("\tlabel=\"%s\";\n", g.GetName())
 	//out += "\tnode [shape=box];\n"
 	str := ""
-	for i := range g.Adjacency { // reverse paths
+	for i := range g.adjacency { // reverse paths
 		out += fmt.Sprintf("\t\"%s\" [label=\"%s[%s]\"];\n", i.GetName(), i.GetKind(), i.GetName())
-		for j := range g.Adjacency[i] {
-			k := g.Adjacency[i][j]
+		for j := range g.adjacency[i] {
+			k := g.adjacency[i][j]
 			// use str for clearer output ordering
 			if k.Notify {
 				str += fmt.Sprintf("\t\"%s\" -> \"%s\" [label=\"%s\",style=bold];\n", i.GetName(), j.GetName(), k.Name)
--- a/pgraph/pgraph.go
+++ b/pgraph/pgraph.go
@@ -54,8 +54,12 @@ type Flags struct {
 // * IOW, you might see package -> file -> service (where package runs first)
 // * This is also the direction that the notify should happen in...
 type Graph struct {
-	Name      string
-	Adjacency map[*Vertex]map[*Vertex]*Edge // *Vertex -> *Vertex (edge)
+	Name string
+
+	adjacency map[*Vertex]map[*Vertex]*Edge // *Vertex -> *Vertex (edge)
+	kv        map[string]interface{}        // some values associated with the graph
+
+	// legacy
 	Flags     Flags
 	state     graphState
 	fastPause bool        // used to disable pokes for a fast pause
@@ -81,18 +85,34 @@ type Edge struct {
 	refresh bool // is there a notify pending for the dest vertex ?
 }

-// NewGraph builds a new graph.
-func NewGraph(name string) *Graph {
-	return &Graph{
-		Name:      name,
-		Adjacency: make(map[*Vertex]map[*Vertex]*Edge),
-		state:     graphStateNil,
-		// ptr b/c: Mutex/WaitGroup must not be copied after first use
-		mutex: &sync.Mutex{},
-		wg:    &sync.WaitGroup{},
-		semas: make(map[string]*semaphore.Semaphore),
-		slock: &sync.Mutex{},
+// Init initializes the graph which populates all the internal structures.
+func (g *Graph) Init() error {
+	if g.Name == "" {
+		return fmt.Errorf("can't initialize graph with empty name")
 	}
+
+	g.adjacency = make(map[*Vertex]map[*Vertex]*Edge)
+	g.kv = make(map[string]interface{})
+
+	// legacy
+	g.state = graphStateNil
+	// ptr b/c: Mutex/WaitGroup must not be copied after first use
+	g.mutex = &sync.Mutex{}
+	g.wg = &sync.WaitGroup{}
+	g.semas = make(map[string]*semaphore.Semaphore)
+	g.slock = &sync.Mutex{}
+	return nil
+}
+
+// NewGraph builds a new graph.
+func NewGraph(name string) (*Graph, error) {
+	g := &Graph{
+		Name: name,
+	}
+	if err := g.Init(); err != nil {
+		return nil, err
+	}
+	return g, nil
 }

 // NewVertex returns a new graph vertex struct with a contained resource.
@@ -119,11 +139,25 @@ func (obj *Edge) SetRefresh(b bool) {
 	obj.refresh = b
 }

+// Value returns a value stored alongside the graph in a particular key.
+func (g *Graph) Value(key string) (interface{}, bool) {
+	val, exists := g.kv[key]
+	return val, exists
+}
+
+// SetValue sets a value to be stored alongside the graph in a particular key.
+func (g *Graph) SetValue(key string, val interface{}) {
+	g.kv[key] = val
+}
+
 // Copy makes a copy of the graph struct
 func (g *Graph) Copy() *Graph {
 	newGraph := &Graph{
 		Name:      g.Name,
-		Adjacency: make(map[*Vertex]map[*Vertex]*Edge, len(g.Adjacency)),
+		adjacency: make(map[*Vertex]map[*Vertex]*Edge, len(g.adjacency)),
+		kv:        g.kv,
+
+		// legacy
 		Flags:     g.Flags,
 		state:     g.state,
 		mutex:     g.mutex,
@@ -134,8 +168,8 @@ func (g *Graph) Copy() *Graph {

 		prometheus: g.prometheus,
 	}
-	for k, v := range g.Adjacency {
-		newGraph.Adjacency[k] = v // copy
+	for k, v := range g.adjacency {
+		newGraph.adjacency[k] = v // copy
 	}
 	return newGraph
 }
@@ -171,17 +205,17 @@ func (g *Graph) setState(state graphState) graphState {
 // AddVertex uses variadic input to add all listed vertices to the graph
 func (g *Graph) AddVertex(xv ...*Vertex) {
 	for _, v := range xv {
-		if _, exists := g.Adjacency[v]; !exists {
-			g.Adjacency[v] = make(map[*Vertex]*Edge)
+		if _, exists := g.adjacency[v]; !exists {
+			g.adjacency[v] = make(map[*Vertex]*Edge)
 		}
 	}
 }

 // DeleteVertex deletes a particular vertex from the graph.
 func (g *Graph) DeleteVertex(v *Vertex) {
-	delete(g.Adjacency, v)
-	for k := range g.Adjacency {
-		delete(g.Adjacency[k], v)
+	delete(g.adjacency, v)
+	for k := range g.adjacency {
+		delete(g.adjacency[k], v)
 	}
 }

@@ -191,16 +225,16 @@ func (g *Graph) AddEdge(v1, v2 *Vertex, e *Edge) {
 	g.AddVertex(v1, v2) // supports adding N vertices now
 	// TODO: check if an edge exists to avoid overwriting it!
 	// NOTE: VertexMerge() depends on overwriting it at the moment...
-	g.Adjacency[v1][v2] = e
+	g.adjacency[v1][v2] = e
 }

 // DeleteEdge deletes a particular edge from the graph.
 // FIXME: add test cases
 func (g *Graph) DeleteEdge(e *Edge) {
-	for v1 := range g.Adjacency {
-		for v2, edge := range g.Adjacency[v1] {
+	for v1 := range g.adjacency {
+		for v2, edge := range g.adjacency[v1] {
 			if e == edge {
-				delete(g.Adjacency[v1], v2)
+				delete(g.adjacency[v1], v2)
 			}
 		}
 	}
@@ -209,7 +243,7 @@ func (g *Graph) DeleteEdge(e *Edge) {
 // CompareMatch searches for an equivalent resource in the graph and returns the
 // vertex it is found in, or nil if not found.
 func (g *Graph) CompareMatch(obj resources.Res) *Vertex {
-	for v := range g.Adjacency {
+	for v := range g.adjacency {
 		if v.Res.Compare(obj) {
 			return v
 		}
@@ -219,7 +253,7 @@ func (g *Graph) CompareMatch(obj resources.Res) *Vertex {

 // TODO: consider adding a mutate API.
 //func (g *Graph) MutateMatch(obj resources.Res) *Vertex {
-//	for v := range g.Adjacency {
+//	for v := range g.adjacency {
 //		if err := v.Res.Mutate(obj); err == nil {
 //			// transmogrified!
 //			return v
@@ -230,7 +264,7 @@ func (g *Graph) CompareMatch(obj resources.Res) *Vertex {

 // HasVertex returns if the input vertex exists in the graph.
 func (g *Graph) HasVertex(v *Vertex) bool {
-	if _, exists := g.Adjacency[v]; exists {
+	if _, exists := g.adjacency[v]; exists {
 		return true
 	}
 	return false
@@ -238,14 +272,14 @@ func (g *Graph) HasVertex(v *Vertex) bool {

 // NumVertices returns the number of vertices in the graph.
 func (g *Graph) NumVertices() int {
-	return len(g.Adjacency)
+	return len(g.adjacency)
 }

 // NumEdges returns the number of edges in the graph.
 func (g *Graph) NumEdges() int {
 	count := 0
-	for k := range g.Adjacency {
-		count += len(g.Adjacency[k])
+	for k := range g.adjacency {
+		count += len(g.adjacency[k])
 	}
 	return count
 }
@@ -254,7 +288,7 @@ func (g *Graph) NumEdges() int {
 // The order is random, because the map implementation is intentionally so!
 func (g *Graph) GetVertices() []*Vertex {
 	var vertices []*Vertex
-	for k := range g.Adjacency {
+	for k := range g.adjacency {
 		vertices = append(vertices, k)
 	}
 	return vertices
@@ -264,7 +298,7 @@ func (g *Graph) GetVertices() []*Vertex {
 func (g *Graph) GetVerticesChan() chan *Vertex {
 	ch := make(chan *Vertex)
 	go func(ch chan *Vertex) {
-		for k := range g.Adjacency {
+		for k := range g.adjacency {
 			ch <- k
 		}
 		close(ch)
@@ -283,7 +317,7 @@ func (vs VertexSlice) Less(i, j int) bool { return vs[i].String() < vs[j].String
 // The order is sorted by String() to avoid the non-determinism in the map type
 func (g *Graph) GetVerticesSorted() []*Vertex {
 	var vertices []*Vertex
-	for k := range g.Adjacency {
+	for k := range g.adjacency {
 		vertices = append(vertices, k)
 	}
 	sort.Sort(VertexSlice(vertices)) // add determinism
@@ -306,8 +340,8 @@ func (g *Graph) IncomingGraphVertices(v *Vertex) []*Vertex {
 	// TODO: we might be able to implement this differently by reversing
 	// the Adjacency graph and then looping through it again...
 	var s []*Vertex
-	for k := range g.Adjacency { // reverse paths
-		for w := range g.Adjacency[k] {
+	for k := range g.adjacency { // reverse paths
+		for w := range g.adjacency[k] {
 			if w == v {
 				s = append(s, k)
 			}
@@ -320,7 +354,7 @@ func (g *Graph) IncomingGraphVertices(v *Vertex) []*Vertex {
 // points to (v -> ???). Poke should probably use this.
 func (g *Graph) OutgoingGraphVertices(v *Vertex) []*Vertex {
 	var s []*Vertex
-	for k := range g.Adjacency[v] { // forward paths
+	for k := range g.adjacency[v] { // forward paths
 		s = append(s, k)
 	}
 	return s
@@ -338,8 +372,8 @@ func (g *Graph) GraphVertices(v *Vertex) []*Vertex {
 // IncomingGraphEdges returns all of the edges that point to vertex v (??? -> v).
 func (g *Graph) IncomingGraphEdges(v *Vertex) []*Edge {
 	var edges []*Edge
-	for v1 := range g.Adjacency { // reverse paths
-		for v2, e := range g.Adjacency[v1] {
+	for v1 := range g.adjacency { // reverse paths
+		for v2, e := range g.adjacency[v1] {
 			if v2 == v {
 				edges = append(edges, e)
 			}
@@ -351,7 +385,7 @@ func (g *Graph) IncomingGraphEdges(v *Vertex) []*Edge {
 // OutgoingGraphEdges returns all of the edges that point from vertex v (v -> ???).
 func (g *Graph) OutgoingGraphEdges(v *Vertex) []*Edge {
 	var edges []*Edge
-	for _, e := range g.Adjacency[v] { // forward paths
+	for _, e := range g.adjacency[v] { // forward paths
 		edges = append(edges, e)
 	}
 	return edges
@@ -370,7 +404,7 @@ func (g *Graph) GraphEdges(v *Vertex) []*Edge {
 func (g *Graph) DFS(start *Vertex) []*Vertex {
 	var d []*Vertex // discovered
 	var s []*Vertex // stack
-	if _, exists := g.Adjacency[start]; !exists {
+	if _, exists := g.adjacency[start]; !exists {
 		return nil // TODO: error
 	}
 	v := start
@@ -390,64 +424,65 @@ func (g *Graph) DFS(start *Vertex) []*Vertex {
 }

 // FilterGraph builds a new graph containing only vertices from the list.
-func (g *Graph) FilterGraph(name string, vertices []*Vertex) *Graph {
-	newgraph := NewGraph(name)
-	for k1, x := range g.Adjacency {
+func (g *Graph) FilterGraph(name string, vertices []*Vertex) (*Graph, error) {
+	newGraph := &Graph{Name: name}
+	if err := newGraph.Init(); err != nil {
+		return nil, errwrap.Wrapf(err, "could not run FilterGraph() properly")
+	}
+	for k1, x := range g.adjacency {
 		for k2, e := range x {
 			//log.Printf("Filter: %s -> %s # %s", k1.Name, k2.Name, e.Name)
 			if VertexContains(k1, vertices) || VertexContains(k2, vertices) {
-				newgraph.AddEdge(k1, k2, e)
+				newGraph.AddEdge(k1, k2, e)
 			}
 		}
 	}
-	return newgraph
+	return newGraph, nil
 }

-// GetDisconnectedGraphs returns a channel containing the N disconnected graphs
-// in our main graph. We can then process each of these in parallel.
-func (g *Graph) GetDisconnectedGraphs() chan *Graph {
-	ch := make(chan *Graph)
-	go func() {
-		var start *Vertex
-		var d []*Vertex // discovered
-		c := g.NumVertices()
-		for len(d) < c {
+// GetDisconnectedGraphs returns a list containing the N disconnected graphs.
+func (g *Graph) GetDisconnectedGraphs() ([]*Graph, error) {
+	graphs := []*Graph{}
+	var start *Vertex
+	var d []*Vertex // discovered
+	c := g.NumVertices()
+	for len(d) < c {

-			// get an undiscovered vertex to start from
-			for _, s := range g.GetVertices() {
-				if !VertexContains(s, d) {
-					start = s
-				}
+		// get an undiscovered vertex to start from
+		for _, s := range g.GetVertices() {
+			if !VertexContains(s, d) {
+				start = s
 			}
-
-			// dfs through the graph
-			dfs := g.DFS(start)
-			// filter all the collected elements into a new graph
-			newgraph := g.FilterGraph(g.Name, dfs)
-
-			// add number of elements found to found variable
-			d = append(d, dfs...) // extend
-
-			// return this new graph to the channel
-			ch <- newgraph
-
-			// if we've found all the elements, then we're done
-			// otherwise loop through to continue...
 		}
-		close(ch)
-	}()
-	return ch
+
+		// dfs through the graph
+		dfs := g.DFS(start)
+		// filter all the collected elements into a new graph
+		newgraph, err := g.FilterGraph(g.Name, dfs)
+		if err != nil {
+			return nil, errwrap.Wrapf(err, "could not run GetDisconnectedGraphs() properly")
+		}
+		// add number of elements found to found variable
+		d = append(d, dfs...) // extend
+
+		// append this new graph to the list
+		graphs = append(graphs, newgraph)
+
+		// if we've found all the elements, then we're done
+		// otherwise loop through to continue...
+	}
+	return graphs, nil
 }

 // InDegree returns the count of vertices that point to me in one big lookup map.
 func (g *Graph) InDegree() map[*Vertex]int {
 	result := make(map[*Vertex]int)
-	for k := range g.Adjacency {
+	for k := range g.adjacency {
 		result[k] = 0 // initialize
 	}

-	for k := range g.Adjacency {
-		for z := range g.Adjacency[k] {
+	for k := range g.adjacency {
+		for z := range g.adjacency[k] {
 			result[z]++
 		}
 	}
@@ -458,9 +493,9 @@ func (g *Graph) InDegree() map[*Vertex]int {
 func (g *Graph) OutDegree() map[*Vertex]int {
 	result := make(map[*Vertex]int)

-	for k := range g.Adjacency {
+	for k := range g.adjacency {
 		result[k] = 0 // initialize
-		for range g.Adjacency[k] {
+		for range g.adjacency[k] {
 			result[k]++
 		}
 	}
@@ -490,7 +525,7 @@ func (g *Graph) TopologicalSort() ([]*Vertex, error) { // kahn's algorithm
 		v := S[last]
 		S = S[:last]
 		L = append(L, v) // add v to tail of L
-		for n := range g.Adjacency[v] {
+		for n := range g.adjacency[v] {
 			// for each node n remaining in the graph, consume from
 			// remaining, so for remaining[n] > 0
 			if remaining[n] > 0 {
@@ -505,7 +540,7 @@ func (g *Graph) TopologicalSort() ([]*Vertex, error) { // kahn's algorithm
 	// if graph has edges, eg if any value in rem is > 0
 	for c, in := range remaining {
 		if in > 0 {
-			for n := range g.Adjacency[c] {
+			for n := range g.adjacency[c] {
 				if remaining[n] > 0 {
 					return nil, fmt.Errorf("not a dag")
 				}
@@ -563,7 +598,11 @@ func (g *Graph) Reachability(a, b *Vertex) []*Vertex {
 func (g *Graph) GraphSync(oldGraph *Graph) (*Graph, error) {

 	if oldGraph == nil {
-		oldGraph = NewGraph(g.GetName()) // copy over the name
+		var err error
+		oldGraph, err = NewGraph(g.GetName()) // copy over the name
+		if err != nil {
+			return nil, errwrap.Wrapf(err, "could not run GraphSync() properly")
+		}
 	}
 	oldGraph.SetName(g.GetName()) // overwrite the name

@@ -571,7 +610,7 @@ func (g *Graph) GraphSync(oldGraph *Graph) (*Graph, error) {
 	var vertexKeep []*Vertex // list of vertices which are the same in new graph
 	var edgeKeep []*Edge     // list of vertices which are the same in new graph

-	for v := range g.Adjacency { // loop through the vertices (resources)
+	for v := range g.adjacency { // loop through the vertices (resources)
 		res := v.Res // resource
 		var vertex *Vertex

@@ -598,7 +637,7 @@ func (g *Graph) GraphSync(oldGraph *Graph) (*Graph, error) {
 	}

 	// get rid of any vertices we shouldn't keep (that aren't in new graph)
-	for v := range oldGraph.Adjacency {
+	for v := range oldGraph.adjacency {
 		if !VertexContains(v, vertexKeep) {
 			// wait for exit before starting new graph!
 			v.SendEvent(event.EventExit, nil) // sync
@@ -608,8 +647,8 @@ func (g *Graph) GraphSync(oldGraph *Graph) (*Graph, error) {
 	}

 	// compare edges
-	for v1 := range g.Adjacency { // loop through the vertices (resources)
-		for v2, e := range g.Adjacency[v1] {
+	for v1 := range g.adjacency { // loop through the vertices (resources)
+		for v2, e := range g.adjacency[v1] {
 			// we have an edge!

 			// lookup vertices (these should exist now)
@@ -624,18 +663,18 @@ func (g *Graph) GraphSync(oldGraph *Graph) (*Graph, error) {
 				return nil, fmt.Errorf("new vertices weren't found") // programming error
 			}

-			edge, exists := oldGraph.Adjacency[vertex1][vertex2]
+			edge, exists := oldGraph.adjacency[vertex1][vertex2]
 			if !exists || edge.Name != e.Name { // TODO: edgeCmp
 				edge = e // use or overwrite edge
 			}
-			oldGraph.Adjacency[vertex1][vertex2] = edge // store it (AddEdge)
+			oldGraph.adjacency[vertex1][vertex2] = edge // store it (AddEdge)
 			edgeKeep = append(edgeKeep, edge)           // mark as saved
 		}
 	}

 	// delete unused edges
-	for v1 := range oldGraph.Adjacency {
-		for _, e := range oldGraph.Adjacency[v1] {
+	for v1 := range oldGraph.adjacency {
+		for _, e := range oldGraph.adjacency[v1] {
 			// we have an edge!
 			if !EdgeContains(e, edgeKeep) {
 				oldGraph.DeleteEdge(e)
@@ -649,7 +688,7 @@ func (g *Graph) GraphSync(oldGraph *Graph) (*Graph, error) {
 // GraphMetas returns a list of pointers to each of the resource MetaParams.
 func (g *Graph) GraphMetas() []*resources.MetaParams {
 	metas := []*resources.MetaParams{}
-	for v := range g.Adjacency { // loop through the vertices (resources))
+	for v := range g.adjacency { // loop through the vertices (resources))
 		res := v.Res // resource
 		meta := res.Meta()
 		metas = append(metas, meta)
@@ -662,7 +701,7 @@ func (g *Graph) AssociateData(data *resources.Data) {
 	// prometheus needs to be associated to this graph as well
 	g.prometheus = data.Prometheus

-	for k := range g.Adjacency {
+	for k := range g.adjacency {
 		*k.Res.Data() = *data
 	}
 }
--- a/pgraph/pgraph_test.go
+++ b/pgraph/pgraph_test.go
@@ -42,7 +42,7 @@ func NV(s string) *Vertex {

 func TestPgraphT1(t *testing.T) {

-	G := NewGraph("g1")
+	G, _ := NewGraph("g1")

 	if i := G.NumVertices(); i != 0 {
 		t.Errorf("should have 0 vertices instead of: %d", i)
@@ -68,7 +68,7 @@ func TestPgraphT1(t *testing.T) {

 func TestPgraphT2(t *testing.T) {

-	G := NewGraph("g2")
+	G, _ := NewGraph("g2")
 	v1 := NV("v1")
 	v2 := NV("v2")
 	v3 := NV("v3")
@@ -95,7 +95,7 @@ func TestPgraphT2(t *testing.T) {

 func TestPgraphT3(t *testing.T) {

-	G := NewGraph("g3")
+	G, _ := NewGraph("g3")
 	v1 := NV("v1")
 	v2 := NV("v2")
 	v3 := NV("v3")
@@ -136,7 +136,7 @@ func TestPgraphT3(t *testing.T) {

 func TestPgraphT4(t *testing.T) {

-	G := NewGraph("g4")
+	G, _ := NewGraph("g4")
 	v1 := NV("v1")
 	v2 := NV("v2")
 	v3 := NV("v3")
@@ -158,7 +158,7 @@ func TestPgraphT4(t *testing.T) {
 }

 func TestPgraphT5(t *testing.T) {
-	G := NewGraph("g5")
+	G, _ := NewGraph("g5")
 	v1 := NV("v1")
 	v2 := NV("v2")
 	v3 := NV("v3")
@@ -180,14 +180,18 @@ func TestPgraphT5(t *testing.T) {
 	//G.AddEdge(v6, v4, e6)

 	save := []*Vertex{v1, v2, v3}
-	out := G.FilterGraph("new g5", save)
+	out, err := G.FilterGraph("new g5", save)
+	if err != nil {
+		t.Errorf("failed with: %v", err)
+	}
+
 	if i := out.NumVertices(); i != 3 {
 		t.Errorf("should have 3 vertices instead of: %d", i)
 	}
 }

 func TestPgraphT6(t *testing.T) {
-	G := NewGraph("g6")
+	G, _ := NewGraph("g6")
 	v1 := NV("v1")
 	v2 := NV("v2")
 	v3 := NV("v3")
@@ -208,24 +212,19 @@ func TestPgraphT6(t *testing.T) {
 	G.AddEdge(v5, v6, e5)
 	//G.AddEdge(v6, v4, e6)

-	graphs := G.GetDisconnectedGraphs()
-	HeisenbergGraphCount := func(ch chan *Graph) int {
-		c := 0
-		for x := range ch {
-			_ = x
-			c++
-		}
-		return c
+	graphs, err := G.GetDisconnectedGraphs()
+	if err != nil {
+		t.Errorf("failed with: %v", err)
 	}

-	if i := HeisenbergGraphCount(graphs); i != 2 {
+	if i := len(graphs); i != 2 {
 		t.Errorf("should have 2 graphs instead of: %d", i)
 	}
 }

 func TestPgraphT7(t *testing.T) {

-	G := NewGraph("g7")
+	G, _ := NewGraph("g7")
 	v1 := NV("v1")
 	v2 := NV("v2")
 	v3 := NV("v3")
@@ -296,7 +295,7 @@ func TestPgraphT8(t *testing.T) {

 func TestPgraphT9(t *testing.T) {

-	G := NewGraph("g9")
+	G, _ := NewGraph("g9")
 	v1 := NV("v1")
 	v2 := NV("v2")
 	v3 := NV("v3")
@@ -372,7 +371,7 @@ func TestPgraphT9(t *testing.T) {

 func TestPgraphT10(t *testing.T) {

-	G := NewGraph("g10")
+	G, _ := NewGraph("g10")
 	v1 := NV("v1")
 	v2 := NV("v2")
 	v3 := NV("v3")
@@ -400,7 +399,7 @@ func TestPgraphT10(t *testing.T) {
 // empty
 func TestPgraphReachability0(t *testing.T) {
 	{
-		G := NewGraph("g")
+		G, _ := NewGraph("g")
 		result := G.Reachability(nil, nil)
 		if result != nil {
 			t.Logf("reachability failed")
@@ -412,7 +411,7 @@ func TestPgraphReachability0(t *testing.T) {
 		}
 	}
 	{
-		G := NewGraph("g")
+		G, _ := NewGraph("g")
 		v1 := NV("v1")
 		v6 := NV("v6")

@@ -429,7 +428,7 @@ func TestPgraphReachability0(t *testing.T) {
 		}
 	}
 	{
-		G := NewGraph("g")
+		G, _ := NewGraph("g")
 		v1 := NV("v1")
 		v2 := NV("v2")
 		v3 := NV("v3")
@@ -463,7 +462,7 @@ func TestPgraphReachability0(t *testing.T) {

 // simple linear path
 func TestPgraphReachability1(t *testing.T) {
-	G := NewGraph("g")
+	G, _ := NewGraph("g")
 	v1 := NV("v1")
 	v2 := NV("v2")
 	v3 := NV("v3")
@@ -497,7 +496,7 @@ func TestPgraphReachability1(t *testing.T) {

 // pick one of two correct paths
 func TestPgraphReachability2(t *testing.T) {
-	G := NewGraph("g")
+	G, _ := NewGraph("g")
 	v1 := NV("v1")
 	v2 := NV("v2")
 	v3 := NV("v3")
@@ -534,7 +533,7 @@ func TestPgraphReachability2(t *testing.T) {

 // pick shortest path
 func TestPgraphReachability3(t *testing.T) {
-	G := NewGraph("g")
+	G, _ := NewGraph("g")
 	v1 := NV("v1")
 	v2 := NV("v2")
 	v3 := NV("v3")
@@ -569,7 +568,7 @@ func TestPgraphReachability3(t *testing.T) {

 // direct path
 func TestPgraphReachability4(t *testing.T) {
-	G := NewGraph("g")
+	G, _ := NewGraph("g")
 	v1 := NV("v1")
 	v2 := NV("v2")
 	v3 := NV("v3")
@@ -693,7 +692,7 @@ func GraphCmp(g1, g2 *Graph) error {
 	var m = make(map[*Vertex]*Vertex) // g1 to g2 vertex correspondence
 Loop:
 	// check vertices
-	for v1 := range g1.Adjacency { // for each vertex in g1
+	for v1 := range g1.adjacency { // for each vertex in g1

 		l1 := strings.Split(v1.GetName(), ",") // make list of everyone's names...
 		for _, x1 := range v1.GetGroup() {
@@ -703,7 +702,7 @@ Loop:
 		sort.Strings(l1)

 		// inner loop
-		for v2 := range g2.Adjacency { // does it match in g2 ?
+		for v2 := range g2.adjacency { // does it match in g2 ?

 			l2 := strings.Split(v2.GetName(), ",")
 			for _, x2 := range v2.GetGroup() {
@@ -723,16 +722,16 @@ Loop:
 	// vertices (and groups) match :)

 	// check edges
-	for v1 := range g1.Adjacency { // for each vertex in g1
+	for v1 := range g1.adjacency { // for each vertex in g1
 		v2 := m[v1] // lookup in map to get correspondance
-		// g1.Adjacency[v1] corresponds to g2.Adjacency[v2]
-		if e1, e2 := len(g1.Adjacency[v1]), len(g2.Adjacency[v2]); e1 != e2 {
+		// g1.adjacency[v1] corresponds to g2.adjacency[v2]
+		if e1, e2 := len(g1.adjacency[v1]), len(g2.adjacency[v2]); e1 != e2 {
 			return fmt.Errorf("graph g1, vertex(%v) has %d edges, while g2, vertex(%v) has %d", v1.GetName(), e1, v2.GetName(), e2)
 		}

-		for vv1, ee1 := range g1.Adjacency[v1] {
+		for vv1, ee1 := range g1.adjacency[v1] {
 			vv2 := m[vv1]
-			ee2 := g2.Adjacency[v2][vv2]
+			ee2 := g2.adjacency[v2][vv2]

 			// these are edges from v1 -> vv1 via ee1 (graph 1)
 			// to cmp to edges from v2 -> vv2 via ee2 (graph 2)
@@ -765,8 +764,8 @@ Loop:
 	}

 	// check meta parameters
-	for v1 := range g1.Adjacency { // for each vertex in g1
-		for v2 := range g2.Adjacency { // does it match in g2 ?
+	for v1 := range g1.adjacency { // for each vertex in g1
+		for v2 := range g2.adjacency { // does it match in g2 ?
 			s1, s2 := v1.Meta().Sema, v2.Meta().Sema
 			sort.Strings(s1)
 			sort.Strings(s2)
@@ -816,7 +815,7 @@ func (ag *testGrouper) edgeMerge(e1, e2 *Edge) *Edge {

 func (g *Graph) fullPrint() (str string) {
 	str += "\n"
-	for v := range g.Adjacency {
+	for v := range g.adjacency {
 		if semas := v.Meta().Sema; len(semas) > 0 {
 			str += fmt.Sprintf("* v: %v; sema: %v\n", v.GetName(), semas)
 		} else {
@@ -824,8 +823,8 @@ func (g *Graph) fullPrint() (str string) {
 		}
 		// TODO: add explicit grouping data?
 	}
-	for v1 := range g.Adjacency {
-		for v2, e := range g.Adjacency[v1] {
+	for v1 := range g.adjacency {
+		for v2, e := range g.adjacency[v1] {
 			str += fmt.Sprintf("* e: %v -> %v # %v\n", v1.GetName(), v2.GetName(), e.Name)
 		}
 	}
--- a/pgraph/semaphore_test.go
+++ b/pgraph/semaphore_test.go
@@ -52,7 +52,7 @@ func NewNoopResTestSema(name string, semas []string) *NoopResTest {
 }

 func TestPgraphSemaphoreGrouping1(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
+	g1, _ := NewGraph("g1") // original graph
 	{
 		a1 := NewVertex(NewNoopResTestSema("a1", []string{"s:1"}))
 		a2 := NewVertex(NewNoopResTestSema("a2", []string{"s:2"}))
@@ -61,7 +61,7 @@ func TestPgraphSemaphoreGrouping1(t *testing.T) {
 		g1.AddVertex(a2)
 		g1.AddVertex(a3)
 	}
-	g2 := NewGraph("g2") // expected result
+	g2, _ := NewGraph("g2") // expected result
 	{
 		a123 := NewVertex(NewNoopResTestSema("a1,a2,a3", []string{"s:1", "s:2", "s:3"}))
 		g2.AddVertex(a123)
@@ -70,7 +70,7 @@ func TestPgraphSemaphoreGrouping1(t *testing.T) {
 }

 func TestPgraphSemaphoreGrouping2(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
+	g1, _ := NewGraph("g1") // original graph
 	{
 		a1 := NewVertex(NewNoopResTestSema("a1", []string{"s:10", "s:11"}))
 		a2 := NewVertex(NewNoopResTestSema("a2", []string{"s:2"}))
@@ -79,7 +79,7 @@ func TestPgraphSemaphoreGrouping2(t *testing.T) {
 		g1.AddVertex(a2)
 		g1.AddVertex(a3)
 	}
-	g2 := NewGraph("g2") // expected result
+	g2, _ := NewGraph("g2") // expected result
 	{
 		a123 := NewVertex(NewNoopResTestSema("a1,a2,a3", []string{"s:10", "s:11", "s:2", "s:3"}))
 		g2.AddVertex(a123)
@@ -88,7 +88,7 @@ func TestPgraphSemaphoreGrouping2(t *testing.T) {
 }

 func TestPgraphSemaphoreGrouping3(t *testing.T) {
-	g1 := NewGraph("g1") // original graph
+	g1, _ := NewGraph("g1") // original graph
 	{
 		a1 := NewVertex(NewNoopResTestSema("a1", []string{"s:1", "s:2"}))
 		a2 := NewVertex(NewNoopResTestSema("a2", []string{"s:2"}))
@@ -97,7 +97,7 @@ func TestPgraphSemaphoreGrouping3(t *testing.T) {
 		g1.AddVertex(a2)
 		g1.AddVertex(a3)
 	}
-	g2 := NewGraph("g2") // expected result
+	g2, _ := NewGraph("g2") // expected result
 	{
 		a123 := NewVertex(NewNoopResTestSema("a1,a2,a3", []string{"s:1", "s:2", "s:3"}))
 		g2.AddVertex(a123)
--- a/test/shell/libmgmt-change1.go
+++ b/test/shell/libmgmt-change1.go
@@ -57,7 +57,10 @@ func (obj *MyGAPI) Graph() (*pgraph.Graph, error) {
 	}
 	// FIXME: these are being specified temporarily until it's the default!
 	metaparams := resources.DefaultMetaParams
-	g := pgraph.NewGraph(obj.Name)
+	g, err := pgraph.NewGraph(obj.Name)
+	if err != nil {
+		return nil, err
+	}

 	n0 := &resources.NoopRes{
 		BaseRes: resources.BaseRes{
--- a/yamlgraph/gconfig.go
+++ b/yamlgraph/gconfig.go
@@ -29,6 +29,7 @@ import (
 	"github.com/purpleidea/mgmt/pgraph"
 	"github.com/purpleidea/mgmt/resources"

+	errwrap "github.com/pkg/errors"
 	"gopkg.in/yaml.v2"
 )

@@ -95,8 +96,12 @@ func (c *GraphConfig) Parse(data []byte) error {
 func (c *GraphConfig) NewGraphFromConfig(hostname string, world resources.World, noop bool) (*pgraph.Graph, error) {
 	// hostname is the uuid for the host

-	var graph *pgraph.Graph          // new graph to return
-	graph = pgraph.NewGraph("Graph") // give graph a default name
+	var graph *pgraph.Graph // new graph to return
+	var err error
+	graph, err = pgraph.NewGraph("Graph") // give graph a default name
+	if err != nil {
+		return nil, errwrap.Wrapf(err, "could not run NewGraphFromConfig() properly")
+	}

 	var lookup = make(map[string]map[string]*pgraph.Vertex)

--- a/yamlgraph2/gconfig.go
+++ b/yamlgraph2/gconfig.go
@@ -28,6 +28,7 @@ import (
 	"github.com/purpleidea/mgmt/pgraph"
 	"github.com/purpleidea/mgmt/resources"

+	errwrap "github.com/pkg/errors"
 	"gopkg.in/yaml.v2"
 )

@@ -155,8 +156,12 @@ func (c *GraphConfig) Parse(data []byte) error {
 func (c *GraphConfig) NewGraphFromConfig(hostname string, world resources.World, noop bool) (*pgraph.Graph, error) {
 	// hostname is the uuid for the host

-	var graph *pgraph.Graph          // new graph to return
-	graph = pgraph.NewGraph("Graph") // give graph a default name
+	var graph *pgraph.Graph // new graph to return
+	var err error
+	graph, err = pgraph.NewGraph("Graph") // give graph a default name
+	if err != nil {
+		return nil, errwrap.Wrapf(err, "could not run NewGraphFromConfig() properly")
+	}

 	var lookup = make(map[string]map[string]*pgraph.Vertex)