Refactor: extract multitenant collection of 'live' reports

To help clarify subsequent changes

app/multitenant/aws_collector.go

@@ -145,13 +145,6 @@ type AWSCollectorConfig struct {
 	CollectorAddr  string
 }
 
-// if StoreInterval is set, reports are merged into here and held until flushed to store
-type pendingEntry struct {
-	sync.Mutex
-	report report.Report
-	count  int
-}
-
 type awsCollector struct {
 	cfg       AWSCollectorConfig
 	db        *dynamodb.DynamoDB
@@ -707,16 +700,8 @@ func (c *awsCollector) Add(ctx context.Context, rep report.Report, buf []byte) e
 		return nil
 	}
 
-	// We are building up a report in memory; merge into that and it will be saved shortly
 	rep = c.massageReport(userid, rep)
-	entry := &pendingEntry{report: report.MakeReport()}
-	if e, found := c.pending.LoadOrStore(userid, entry); found {
-		entry = e.(*pendingEntry)
-	}
-	entry.Lock()
-	entry.report.UnsafeMerge(rep)
-	entry.count++
-	entry.Unlock()
+	c.addToLive(ctx, userid, rep)
 
 	return nil
 }

app/multitenant/collector.go

@@ -0,0 +1,34 @@
+package multitenant
+
+// Collect reports from probes per-tenant, and supply them to queriers on demand
+
+import (
+	"sync"
+
+	"context"
+
+	"github.com/weaveworks/scope/report"
+)
+
+// if StoreInterval is set, reports are merged into here and held until flushed to store
+type pendingEntry struct {
+	sync.Mutex
+	report *report.Report
+}
+
+// We are building up a report in memory; merge into that and it will be saved shortly
+// NOTE: may retain a reference to rep; must not be used by caller after this.
+func (c *awsCollector) addToLive(ctx context.Context, userid string, rep report.Report) {
+	entry := &pendingEntry{}
+	if e, found := c.pending.LoadOrStore(userid, entry); found {
+		entry = e.(*pendingEntry)
+	}
+	entry.Lock()
+	if entry.report == nil {
+		entry.report = &rep
+	} else {
+		entry.report.UnsafeMerge(rep)
+	}
+	entry.Unlock()
+}
+