Exit joinResults.result() if context cancelled

These can be long-running operations, and if the client retries we get
the cancelled one running in parallel with the retry, slowing both down
and making it likely the next one will time out too.

render/container.go

@@ -275,7 +275,7 @@ func (m containerImageRenderer) Render(ctx context.Context, rpt report.Report) N
 		id := report.MakeContainerImageNodeID(imageID)
 		ret.addChildAndChildren(n, id, report.ContainerImage)
 	}
-	return ret.result(containers)
+	return ret.result(ctx, containers)
 }
 
 func containerImageNodeID(n report.Node) string {
@@ -328,5 +328,5 @@ func (m containerHostnameRenderer) Render(ctx context.Context, rpt report.Report
 		}
 		ret.addChildAndChildren(n, id, containerHostnameTopology)
 	}
-	return ret.result(containers)
+	return ret.result(ctx, containers)
 }

render/endpoint.go

@@ -47,5 +47,5 @@ func (e mapEndpoints) Render(ctx context.Context, rpt report.Report) Nodes {
 			ret.addChild(n, id, e.topology)
 		}
 	}
-	return ret.result(endpoints)
+	return ret.result(ctx, endpoints)
 }

render/filters.go

@@ -17,7 +17,7 @@ const (
 // in one call - useful for functions that need to consider the entire graph.
 // We should minimise the use of this renderer type, as it is very inflexible.
 type CustomRenderer struct {
-	RenderFunc func(Nodes) Nodes
+	RenderFunc func(context.Context, Nodes) Nodes
 	Renderer
 }
 
@@ -26,7 +26,7 @@ func (c CustomRenderer) Render(ctx context.Context, rpt report.Report) Nodes {
 	if ctx.Err() != nil {
 		return Nodes{}
 	}
-	return c.RenderFunc(c.Renderer.Render(ctx, rpt))
+	return c.RenderFunc(ctx, c.Renderer.Render(ctx, rpt))
 }
 
 // FilterFunc is the function type used by Filters
@@ -189,7 +189,7 @@ func filterInternetAdjacencies(nodes report.Nodes) {
 func ColorConnected(r Renderer) Renderer {
 	return CustomRenderer{
 		Renderer: r,
-		RenderFunc: func(input Nodes) Nodes {
+		RenderFunc: func(ctx context.Context, input Nodes) Nodes {
 			output := input.Copy()
 			for id := range connected(input.Nodes) {
 				output[id] = output[id].WithLatest(IsConnectedMark, mtime.Now(), "true")

render/host.go

@@ -1,6 +1,8 @@
 package render
 
 import (
+	"context"
+
 	"github.com/weaveworks/scope/report"
 )
 
@@ -25,7 +27,7 @@ var HostRenderer = MakeReduce(
 // format for a host, but without any Major or Minor labels.  It does
 // not have enough info to do that, and the resulting graph must be
 // merged with a host graph to get that info.
-func nodes2Hosts(nodes Nodes) Nodes {
+func nodes2Hosts(ctx context.Context, nodes Nodes) Nodes {
 	ret := newJoinResults(nil)
 
 	for _, n := range nodes.Nodes {
@@ -47,7 +49,7 @@ func nodes2Hosts(nodes Nodes) Nodes {
 			}
 		}
 	}
-	return ret.result(nodes)
+	return ret.result(ctx, nodes)
 }
 
 func endpoint2Host(n report.Node) string {

render/pod.go

@@ -197,5 +197,5 @@ func (m Map2Parent) Render(ctx context.Context, rpt report.Report) Nodes {
 			ret.addChildAndChildren(n, id, Pseudo)
 		}
 	}
-	return ret.result(input)
+	return ret.result(ctx, input)
 }

render/process.go

@@ -95,7 +95,7 @@ func hasMoreThanOneConnection(n report.Node, endpoints report.Nodes) bool {
 var processNameTopology = MakeGroupNodeTopology(report.Process, report.Name)
 
 // processes2Names maps process Nodes to Nodes for each process name.
-func processes2Names(processes Nodes) Nodes {
+func processes2Names(ctx context.Context, processes Nodes) Nodes {
 	ret := newJoinResults(nil)
 
 	for _, n := range processes.Nodes {
@@ -105,5 +105,5 @@ func processes2Names(processes Nodes) Nodes {
 			ret.addChildAndChildren(n, name, processNameTopology)
 		}
 	}
-	return ret.result(processes)
+	return ret.result(ctx, processes)
 }

render/render.go

@@ -133,7 +133,7 @@ func (m Map) Render(ctx context.Context, rpt report.Report) Nodes {
 	span.LogFields(otlog.Int("input.nodes", len(input.Nodes)),
 		otlog.Int("ouput.nodes", len(output.nodes)))
 
-	return output.result(input)
+	return output.result(ctx, input)
 }
 
 // Condition is a predecate over the entire report that can evaluate to true or false.
@@ -233,8 +233,11 @@ func (ret *joinResults) passThrough(n report.Node) {
 
 // Rewrite Adjacency of nodes in ret mapped from original nodes in
 // input, and return the result.
-func (ret *joinResults) result(input Nodes) Nodes {
+func (ret *joinResults) result(ctx context.Context, input Nodes) Nodes {
 	for _, n := range input.Nodes {
+		if ctx.Err() != nil { // check if cancelled
+			return Nodes{}
+		}
 		outID, ok := ret.mapped[n.ID]
 		if !ok {
 			continue