Add top level and per-mutator traces to soong_build

- Top-level trace for all soong_build runs
  - Includes adding Peek() to OncePer because not all soong_build
    invocations have GenerateBuildActions run.
- A trace per mutator invocation

Test: m && build/bazel/scripts/print_analysis_metrics.py
Change-Id: Ief5c04630484fb38ec7e3757de45c7dc294d3b3c

android/metrics.go

@@ -32,8 +32,13 @@ type SoongMetrics struct {
 	Variants int
 }
 
-func ReadSoongMetrics(config Config) SoongMetrics {
-	return config.Get(soongMetricsOnceKey).(SoongMetrics)
+func readSoongMetrics(config Config) (SoongMetrics, bool) {
+	soongMetrics, ok := config.Peek(soongMetricsOnceKey)
+	if ok {
+		return soongMetrics.(SoongMetrics), true
+	} else {
+		return SoongMetrics{}, false
+	}
 }
 
 func init() {
@@ -60,9 +65,11 @@ func (soongMetricsSingleton) GenerateBuildActions(ctx SingletonContext) {
 func collectMetrics(config Config, eventHandler metrics.EventHandler) *soong_metrics_proto.SoongBuildMetrics {
 	metrics := &soong_metrics_proto.SoongBuildMetrics{}
 
-	soongMetrics := ReadSoongMetrics(config)
-	metrics.Modules = proto.Uint32(uint32(soongMetrics.Modules))
-	metrics.Variants = proto.Uint32(uint32(soongMetrics.Variants))
+	soongMetrics, ok := readSoongMetrics(config)
+	if ok {
+		metrics.Modules = proto.Uint32(uint32(soongMetrics.Modules))
+		metrics.Variants = proto.Uint32(uint32(soongMetrics.Variants))
+	}
 
 	memStats := runtime.MemStats{}
 	runtime.ReadMemStats(&memStats)

android/onceper.go

@@ -79,6 +79,17 @@ func (once *OncePer) Get(key OnceKey) interface{} {
 	return once.maybeWaitFor(key, v)
 }
 
+// Peek returns the value previously computed with Once for a given key.  If Once has not
+// been called for the given key Peek will return ok == false.
+func (once *OncePer) Peek(key OnceKey) (interface{}, bool) {
+	v, ok := once.values.Load(key)
+	if !ok {
+		return nil, false
+	}
+
+	return once.maybeWaitFor(key, v), true
+}
+
 // OnceStringSlice is the same as Once, but returns the value cast to a []string
 func (once *OncePer) OnceStringSlice(key OnceKey, value func() []string) []string {
 	return once.Once(key, func() interface{} { return value() }).([]string)

cmd/soong_build/main.go

@@ -220,7 +220,7 @@ func writeDepFile(outputFile string, eventHandler metrics.EventHandler, ninjaDep
 // doChosenActivity runs Soong for a specific activity, like bp2build, queryview
 // or the actual Soong build for the build.ninja file. Returns the top level
 // output file of the specific activity.
-func doChosenActivity(configuration android.Config, extraNinjaDeps []string, logDir string) string {
+func doChosenActivity(ctx *android.Context, configuration android.Config, extraNinjaDeps []string, logDir string) string {
 	mixedModeBuild := configuration.BazelContext.BazelEnabled()
 	generateBazelWorkspace := bp2buildMarker != ""
 	generateQueryView := bazelQueryViewDir != ""
@@ -236,7 +236,6 @@ func doChosenActivity(configuration android.Config, extraNinjaDeps []string, log
 
 	blueprintArgs := cmdlineArgs
 
-	ctx := newContext(configuration)
 	if mixedModeBuild {
 		runMixedModeBuild(configuration, ctx, extraNinjaDeps)
 	} else {
@@ -284,7 +283,6 @@ func doChosenActivity(configuration android.Config, extraNinjaDeps []string, log
 		}
 	}
 
-	writeMetrics(configuration, *ctx.EventHandler, logDir)
 	return cmdlineArgs.OutFile
 }
 
@@ -344,7 +342,13 @@ func main() {
 	// change between every CI build, so tracking it would require re-running Soong for every build.
 	logDir := availableEnv["LOG_DIR"]
 
-	finalOutputFile := doChosenActivity(configuration, extraNinjaDeps, logDir)
+	ctx := newContext(configuration)
+	ctx.EventHandler.Begin("soong_build")
+
+	finalOutputFile := doChosenActivity(ctx, configuration, extraNinjaDeps, logDir)
+
+	ctx.EventHandler.End("soong_build")
+	writeMetrics(configuration, *ctx.EventHandler, logDir)
 
 	writeUsedEnvironmentFile(configuration, finalOutputFile)
 }