Requires that metrics with the same name have the same Kind.

The store add enforces that the first metric added to the store is the
definitive Kind of a metric.  All subsequent metrics added must have that kind,
or the program load fails.

Issue #59

Makefile

@@ -39,6 +39,7 @@ GOTESTFILES=\
 	exporter/varz_test.go\
 	metrics/datum/int_test.go\
 	metrics/metric_test.go\
+	metrics/store_test.go\
 	mtail/mtail_test.go\
 	tailer/tail_test.go\
 	testdata/reader.go\

metrics/store.go

@@ -5,6 +5,7 @@ package metrics
 
 import (
 	"encoding/json"
+	"fmt"
 	"sync"
 )
 
@@ -21,10 +22,17 @@ func NewStore() (s *Store) {
 }
 
 // Add is used to add one metric to the Store.
-func (s *Store) Add(m *Metric) {
+func (s *Store) Add(m *Metric) error {
 	s.Lock()
 	defer s.Unlock()
+	if len(s.Metrics[m.Name]) > 0 {
+		t := s.Metrics[m.Name][0].Kind
+		if m.Kind != t {
+			return fmt.Errorf("Metric %s has different kind %s to existing %s.", m.Name, m.Kind, t)
+		}
+	}
 	s.Metrics[m.Name] = append(s.Metrics[m.Name], m)
+	return nil
 }
 
 // ClearMetrics empties the store of all metrics.

metrics/store_test.go

@@ -0,0 +1,20 @@
+// Copyright 2017 Google Inc. All Rights Reserved.
+// This file is available under the Apache license.
+
+package metrics
+
+import "testing"
+
+func TestMatchingKind(t *testing.T) {
+	s := NewStore()
+	m1 := NewMetric("foo", "prog", Counter, Int)
+	err := s.Add(m1)
+	if err != nil {
+		t.Fatalf("should be nil: %s", err)
+	}
+	m2 := NewMetric("foo", "prog1", Gauge, Int)
+	err = s.Add(m2)
+	if err == nil {
+		t.Fatal("should be err")
+	}
+}

vm/loader.go

@@ -165,31 +165,46 @@ func (l *Loader) CompileAndRun(name string, input io.Reader) error {
 		ProgLoadErrors.Add(name, 1)
 		return fmt.Errorf("Internal error: Compilation failed for %s: No program returned, but no errors.", name)
 	}
+
+	if l.dumpBytecode {
+		glog.Info("Dumping program objects and bytecode\n", v.DumpByteCode(name))
+	}
+
+	// Load the metrics from the compilation into the global metric storage for export.
 	for _, m := range v.m {
 		if !m.Hidden {
-			l.ms.Add(m)
+			err := l.ms.Add(m)
+			if err != nil {
+				return err
+			}
 		}
 	}
-	if l.dumpBytecode {
-		glog.Info("Dumping program objects and bytecode\n", v.DumpByteCode(name))
-	}
+
+	ProgLoads.Add(name, 1)
+	glog.Infof("Loaded program %s", name)
+
 	if l.compileOnly {
 		return nil
 	}
-	ProgLoads.Add(name, 1)
-	glog.Infof("Loaded program %s", name)
 
 	l.handleMu.Lock()
 	defer l.handleMu.Unlock()
+
 	// Stop any previous VM.
 	if handle, ok := l.handles[name]; ok {
+		glog.Infof("Stopping program %s", name)
 		close(handle.lines)
 		<-handle.done
+		glog.Info("Stopped")
 	}
+
 	l.handles[name] = &vmHandle{make(chan *tailer.LogLine), make(chan struct{})}
 	nameCode := nameToCode(name)
 	glog.Infof("Program %s has goroutine marker 0x%x", name, nameCode)
 	go v.Run(nameCode, l.handles[name].lines, l.handles[name].done)
+
+	glog.Infof("Program %s running", name)
+
 	return nil
 }