cmd/trace: fix a runnable goroutine count bug

When starting tracing, EvGoCreate events are added for existing
goroutines that may have been blocking in syscall. EvGoCreate
increments the runnable goroutine count. This change makes the
following EvGoInSyscall event decrement the runnable goroutine count
because we now know that goroutine is in syscall, and not runnable.

Made generateTrace return an error, at any given time, the number
of runnable/running/insyscall goroutines becomes non-negative.

Added a basic test that checks the number of runnable/running
goroutines don't include the goroutines in syscall - the test failed
before this change.

Change-Id: Ib732c382e7bd17158a437576f9d589ab89097ce6
Reviewed-on: https://go-review.googlesource.com/25552
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

src/cmd/trace/main.go

@@ -89,7 +89,10 @@ func main() {
 		events:  events,
 		endTime: int64(1<<63 - 1),
 	}
-	data := generateTrace(params)
+	data, err := generateTrace(params)
+	if err != nil {
+		dief("%v\n", err)
+	}
 
 	log.Printf("Splitting trace...")
 	ranges = splitTrace(data)

src/cmd/trace/trace.go

@@ -160,7 +160,11 @@ func httpJsonTrace(w http.ResponseWriter, r *http.Request) {
 		params.gs = trace.RelatedGoroutines(events, goid)
 	}
 
-	data := generateTrace(params)
+	data, err := generateTrace(params)
+	if err != nil {
+		log.Printf("failed to generate trace: %v", err)
+		return
+	}
 
 	if startStr, endStr := r.FormValue("start"), r.FormValue("end"); startStr != "" && endStr != "" {
 		// If start/end arguments are present, we are rendering a range of the trace.
@@ -307,7 +311,7 @@ type SortIndexArg struct {
 // If gtrace=true, generate trace for goroutine goid, otherwise whole trace.
 // startTime, endTime determine part of the trace that we are interested in.
 // gset restricts goroutines that are included in the resulting trace.
-func generateTrace(params *traceParams) ViewerData {
+func generateTrace(params *traceParams) (ViewerData, error) {
 	ctx := &traceContext{traceParams: params}
 	ctx.frameTree.children = make(map[uint64]frameNode)
 	ctx.data.Frames = make(map[string]ViewerFrame)
@@ -408,9 +412,10 @@ func generateTrace(params *traceParams) ViewerData {
 			ctx.grunning--
 			ctx.emitGoroutineCounters(ev)
 		case trace.EvGoWaiting:
-			ctx.grunnable--
+			ctx.grunnable-- // cancels out the effect of EvGoCreate at the beginning
 			ctx.emitGoroutineCounters(ev)
 		case trace.EvGoInSyscall:
+			ctx.grunnable-- // cancels out the effect of EvGoCreate at the beginning
 			ctx.insyscall++
 			ctx.emitThreadCounters(ev)
 		case trace.EvHeapAlloc:
@@ -420,6 +425,9 @@ func generateTrace(params *traceParams) ViewerData {
 			ctx.nextGC = ev.Args[0]
 			ctx.emitHeapCounters(ev)
 		}
+		if ctx.grunnable < 0 || ctx.grunning < 0 || ctx.insyscall < 0 {
+			return ctx.data, fmt.Errorf("invalid state after processing %v: runnable=%d running=%d insyscall=%d", ev, ctx.grunnable, ctx.grunning, ctx.insyscall)
+		}
 	}
 
 	ctx.data.footer = len(ctx.data.Events)
@@ -459,7 +467,7 @@ func generateTrace(params *traceParams) ViewerData {
 		ctx.emit(&ViewerEvent{Name: "thread_sort_index", Phase: "M", Pid: 0, Tid: 0, Arg: &SortIndexArg{-1}})
 	}
 
-	return ctx.data
+	return ctx.data, nil
 }
 
 func (ctx *traceContext) emit(e *ViewerEvent) {
@@ -491,11 +499,12 @@ func (ctx *traceContext) emitSlice(ev *trace.Event, name string) {
 	})
 }
 
-func (ctx *traceContext) emitHeapCounters(ev *trace.Event) {
-	type Arg struct {
+type heapCountersArg struct {
 	Allocated uint64
 	NextGC    uint64
-	}
+}
+
+func (ctx *traceContext) emitHeapCounters(ev *trace.Event) {
 	if ctx.gtrace {
 		return
 	}
@@ -503,29 +512,31 @@ func (ctx *traceContext) emitHeapCounters(ev *trace.Event) {
 	if ctx.nextGC > ctx.heapAlloc {
 		diff = ctx.nextGC - ctx.heapAlloc
 	}
-	ctx.emit(&ViewerEvent{Name: "Heap", Phase: "C", Time: ctx.time(ev), Pid: 1, Arg: &Arg{ctx.heapAlloc, diff}})
+	ctx.emit(&ViewerEvent{Name: "Heap", Phase: "C", Time: ctx.time(ev), Pid: 1, Arg: &heapCountersArg{ctx.heapAlloc, diff}})
 }
 
-func (ctx *traceContext) emitGoroutineCounters(ev *trace.Event) {
-	type Arg struct {
+type goroutineCountersArg struct {
 	Running  uint64
 	Runnable uint64
-	}
+}
+
+func (ctx *traceContext) emitGoroutineCounters(ev *trace.Event) {
 	if ctx.gtrace {
 		return
 	}
-	ctx.emit(&ViewerEvent{Name: "Goroutines", Phase: "C", Time: ctx.time(ev), Pid: 1, Arg: &Arg{ctx.grunning, ctx.grunnable}})
+	ctx.emit(&ViewerEvent{Name: "Goroutines", Phase: "C", Time: ctx.time(ev), Pid: 1, Arg: &goroutineCountersArg{ctx.grunning, ctx.grunnable}})
 }
 
-func (ctx *traceContext) emitThreadCounters(ev *trace.Event) {
-	type Arg struct {
+type threadCountersArg struct {
 	Running   uint64
 	InSyscall uint64
-	}
+}
+
+func (ctx *traceContext) emitThreadCounters(ev *trace.Event) {
 	if ctx.gtrace {
 		return
 	}
-	ctx.emit(&ViewerEvent{Name: "Threads", Phase: "C", Time: ctx.time(ev), Pid: 1, Arg: &Arg{ctx.prunning, ctx.insyscall}})
+	ctx.emit(&ViewerEvent{Name: "Threads", Phase: "C", Time: ctx.time(ev), Pid: 1, Arg: &threadCountersArg{ctx.prunning, ctx.insyscall}})
 }
 
 func (ctx *traceContext) emitInstant(ev *trace.Event, name string) {

src/cmd/trace/trace_test.go

+package main
+
+import (
+	"internal/trace"
+	"testing"
+)
+
+// TestGoroutineCount tests runnable/running goroutine counts computed by generateTrace
+// remain in the valid range.
+//   - the counts must not be negative. generateTrace will return an error.
+//   - the counts must not include goroutines blocked waiting on channels or in syscall.
+func TestGoroutineCount(t *testing.T) {
+	w := trace.NewWriter()
+	w.Emit(trace.EvBatch, 0, 0)  // start of per-P batch event [pid, timestamp]
+	w.Emit(trace.EvFrequency, 1) // [ticks per second]
+
+	// In this test, we assume a valid trace contains EvGoWaiting or EvGoInSyscall
+	// event for every blocked goroutine.
+
+	// goroutine 10: blocked
+	w.Emit(trace.EvGoCreate, 1, 10, 1, 1) // [timestamp, new goroutine id, new stack id, stack id]
+	w.Emit(trace.EvGoWaiting, 1, 10)      // [timestamp, goroutine id]
+
+	// goroutine 20: in syscall
+	w.Emit(trace.EvGoCreate, 1, 20, 2, 1)
+	w.Emit(trace.EvGoInSyscall, 1, 20) // [timestamp, goroutine id]
+
+	// goroutine 30: runnable
+	w.Emit(trace.EvGoCreate, 1, 30, 5, 1)
+
+	w.Emit(trace.EvProcStart, 2, 0) // [timestamp, thread id]
+
+	// goroutine 40: runnable->running->runnable
+	w.Emit(trace.EvGoCreate, 1, 40, 7, 1)
+	w.Emit(trace.EvGoStartLocal, 1, 40) // [timestamp, goroutine id]
+	w.Emit(trace.EvGoSched, 1, 8)       // [timestamp, stack]
+
+	events, err := trace.Parse(w, "")
+	if err != nil {
+		t.Fatalf("failed to parse test trace: %v", err)
+	}
+
+	params := &traceParams{
+		events:  events,
+		endTime: int64(1<<63 - 1),
+	}
+
+	// If the counts drop below 0, generateTrace will return an error.
+	viewerData, err := generateTrace(params)
+	if err != nil {
+		t.Fatalf("generateTrace failed: %v", err)
+	}
+	for _, ev := range viewerData.Events {
+		if ev.Name == "Goroutines" {
+			cnt := ev.Arg.(*goroutineCountersArg)
+			if cnt.Runnable+cnt.Running > 2 {
+				t.Errorf("goroutine count=%+v; want no more than 2 goroutines in runnable/running state", cnt)
+			}
+			t.Logf("read %+v %+v", ev, cnt)
+		}
+	}
+}

src/internal/trace/parser_test.go

@@ -90,52 +90,13 @@ func TestParseVersion(t *testing.T) {
 
 func TestTimestampOverflow(t *testing.T) {
 	// Test that parser correctly handles large timestamps (long tracing).
-	w := newWriter()
-	w.emit(EvBatch, 0, 0)
-	w.emit(EvFrequency, 1e9)
+	w := NewWriter()
+	w.Emit(EvBatch, 0, 0)
+	w.Emit(EvFrequency, 1e9)
 	for ts := uint64(1); ts < 1e16; ts *= 2 {
-		w.emit(EvGoCreate, ts, ts, 0, 0)
+		w.Emit(EvGoCreate, ts, ts, 0, 0)
 	}
 	if _, err := Parse(w, ""); err != nil {
 		t.Fatalf("failed to parse: %v", err)
 	}
 }
-
-type writer struct {
-	bytes.Buffer
-}
-
-func newWriter() *writer {
-	w := new(writer)
-	w.Write([]byte("go 1.7 trace\x00\x00\x00\x00"))
-	return w
-}
-
-func (w *writer) emit(typ byte, args ...uint64) {
-	nargs := byte(len(args)) - 1
-	if nargs > 3 {
-		nargs = 3
-	}
-	buf := []byte{typ | nargs<<6}
-	if nargs == 3 {
-		buf = append(buf, 0)
-	}
-	for _, a := range args {
-		buf = appendVarint(buf, a)
-	}
-	if nargs == 3 {
-		buf[1] = byte(len(buf) - 2)
-	}
-	n, err := w.Write(buf)
-	if n != len(buf) || err != nil {
-		panic("failed to write")
-	}
-}
-
-func appendVarint(buf []byte, v uint64) []byte {
-	for ; v >= 0x80; v >>= 7 {
-		buf = append(buf, 0x80|byte(v))
-	}
-	buf = append(buf, byte(v))
-	return buf
-}

src/internal/trace/writer.go

+package trace
+
+import "bytes"
+
+// Writer is a test trace writer.
+type Writer struct {
+	bytes.Buffer
+}
+
+func NewWriter() *Writer {
+	w := new(Writer)
+	w.Write([]byte("go 1.7 trace\x00\x00\x00\x00"))
+	return w
+}
+
+// Emit writes an event record to the trace.
+// See Event types for valid types and required arguments.
+func (w *Writer) Emit(typ byte, args ...uint64) {
+	nargs := byte(len(args)) - 1
+	if nargs > 3 {
+		nargs = 3
+	}
+	buf := []byte{typ | nargs<<6}
+	if nargs == 3 {
+		buf = append(buf, 0)
+	}
+	for _, a := range args {
+		buf = appendVarint(buf, a)
+	}
+	if nargs == 3 {
+		buf[1] = byte(len(buf) - 2)
+	}
+	n, err := w.Write(buf)
+	if n != len(buf) || err != nil {
+		panic("failed to write")
+	}
+}
+
+func appendVarint(buf []byte, v uint64) []byte {
+	for ; v >= 0x80; v >>= 7 {
+		buf = append(buf, 0x80|byte(v))
+	}
+	buf = append(buf, byte(v))
+	return buf
+}