runtime/pprof: sort counted profiles by count

This is especially helpful in programs with very large numbers of goroutines:
the bulk of the goroutines will show up at the top.

Before:
	1 @ 0x86ab8 0x86893 0x82164 0x8e7ce 0x7b798 0x5b871
	#	0x86ab8	runtime/pprof.writeRuntimeProfile+0xb8		/Users/rsc/go/src/runtime/pprof/pprof.go:545
	#	0x86893	runtime/pprof.writeGoroutine+0x93		/Users/rsc/go/src/runtime/pprof/pprof.go:507
	#	0x82164	runtime/pprof.(*Profile).WriteTo+0xd4		/Users/rsc/go/src/runtime/pprof/pprof.go:236
	#	0x8e7ce	runtime/pprof_test.TestGoroutineCounts+0x15e	/Users/rsc/go/src/runtime/pprof/pprof_test.go:603
	#	0x7b798	testing.tRunner+0x98				/Users/rsc/go/src/testing/testing.go:473

	1 @ 0x2d373 0x2d434 0x560f 0x516b 0x7cd42 0x7b861 0x2297 0x2cf90 0x5b871
	#	0x7cd42	testing.RunTests+0x8d2	/Users/rsc/go/src/testing/testing.go:583
	#	0x7b861	testing.(*M).Run+0x81	/Users/rsc/go/src/testing/testing.go:515
	#	0x2297	main.main+0x117		runtime/pprof/_test/_testmain.go:72
	#	0x2cf90	runtime.main+0x2b0	/Users/rsc/go/src/runtime/proc.go:188

	10 @ 0x2d373 0x2d434 0x560f 0x516b 0x8e5b6 0x5b871
	#	0x8e5b6	runtime/pprof_test.func1+0x36	/Users/rsc/go/src/runtime/pprof/pprof_test.go:582

	50 @ 0x2d373 0x2d434 0x560f 0x516b 0x8e656 0x5b871
	#	0x8e656	runtime/pprof_test.func3+0x36	/Users/rsc/go/src/runtime/pprof/pprof_test.go:584

	40 @ 0x2d373 0x2d434 0x560f 0x516b 0x8e606 0x5b871
	#	0x8e606	runtime/pprof_test.func2+0x36	/Users/rsc/go/src/runtime/pprof/pprof_test.go:583

After:

	50 @ 0x2d373 0x2d434 0x560f 0x516b 0x8ecc6 0x5b871
	#	0x8ecc6	runtime/pprof_test.func3+0x36	/Users/rsc/go/src/runtime/pprof/pprof_test.go:584

	40 @ 0x2d373 0x2d434 0x560f 0x516b 0x8ec76 0x5b871
	#	0x8ec76	runtime/pprof_test.func2+0x36	/Users/rsc/go/src/runtime/pprof/pprof_test.go:583

	10 @ 0x2d373 0x2d434 0x560f 0x516b 0x8ec26 0x5b871
	#	0x8ec26	runtime/pprof_test.func1+0x36	/Users/rsc/go/src/runtime/pprof/pprof_test.go:582

	1 @ 0x2d373 0x2d434 0x560f 0x516b 0x7cd42 0x7b861 0x2297 0x2cf90 0x5b871
	#	0x7cd42	testing.RunTests+0x8d2	/Users/rsc/go/src/testing/testing.go:583
	#	0x7b861	testing.(*M).Run+0x81	/Users/rsc/go/src/testing/testing.go:515
	#	0x2297	main.main+0x117		runtime/pprof/_test/_testmain.go:72
	#	0x2cf90	runtime.main+0x2b0	/Users/rsc/go/src/runtime/proc.go:188

	1 @ 0x87128 0x86f03 0x82164 0x8ee30 0x7b798 0x5b871
	#	0x87128	runtime/pprof.writeRuntimeProfile+0xb8		/Users/rsc/go/src/runtime/pprof/pprof.go:566
	#	0x86f03	runtime/pprof.writeGoroutine+0x93		/Users/rsc/go/src/runtime/pprof/pprof.go:528
	#	0x82164	runtime/pprof.(*Profile).WriteTo+0xd4		/Users/rsc/go/src/runtime/pprof/pprof.go:236
	#	0x8ee30	runtime/pprof_test.TestGoroutineCounts+0x150	/Users/rsc/go/src/runtime/pprof/pprof_test.go:603
	#	0x7b798	testing.tRunner+0x98				/Users/rsc/go/src/testing/testing.go:473

Change-Id: I43de9eee2d96f9c46f7b0fbe099a0571164324f5
Reviewed-on: https://go-review.googlesource.com/20107
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/pprof/pprof.go

@@ -296,22 +296,25 @@ func printCountProfile(w io.Writer, debug int, name string, p countProfile) erro
 		}
 		return buf.String()
 	}
-	m := map[string]int{}
+	count := map[string]int{}
+	index := map[string]int{}
+	var keys []string
 	n := p.Len()
 	for i := 0; i < n; i++ {
-		m[key(p.Stack(i))]++
+		k := key(p.Stack(i))
+		if count[k] == 0 {
+			index[k] = i
+			keys = append(keys, k)
+		}
+		count[k]++
 	}
 
-	// Print stacks, listing count on first occurrence of a unique stack.
-	for i := 0; i < n; i++ {
-		stk := p.Stack(i)
-		s := key(stk)
-		if count := m[s]; count != 0 {
-			fmt.Fprintf(w, "%d %s\n", count, s)
-			if debug > 0 {
-				printStackRecord(w, stk, false)
-			}
-			delete(m, s)
+	sort.Sort(&keysByCount{keys, count})
+
+	for _, k := range keys {
+		fmt.Fprintf(w, "%d %s\n", count[k], k)
+		if debug > 0 {
+			printStackRecord(w, p.Stack(index[k]), false)
 		}
 	}
 
@@ -321,6 +324,23 @@ func printCountProfile(w io.Writer, debug int, name string, p countProfile) erro
 	return b.Flush()
 }
 
+// keysByCount sorts keys with higher counts first, breaking ties by key string order.
+type keysByCount struct {
+	keys  []string
+	count map[string]int
+}
+
+func (x *keysByCount) Len() int      { return len(x.keys) }
+func (x *keysByCount) Swap(i, j int) { x.keys[i], x.keys[j] = x.keys[j], x.keys[i] }
+func (x *keysByCount) Less(i, j int) bool {
+	ki, kj := x.keys[i], x.keys[j]
+	ci, cj := x.count[ki], x.count[kj]
+	if ci != cj {
+		return ci > cj
+	}
+	return ki < kj
+}
+
 // printStackRecord prints the function + source line information
 // for a single stack trace.
 func printStackRecord(w io.Writer, stk []uintptr, allFrames bool) {

src/runtime/pprof/pprof_test.go

@@ -578,3 +578,47 @@ func blockCond() {
 	c.Wait()
 	mu.Unlock()
 }
+
+func func1(c chan int) { <-c }
+func func2(c chan int) { <-c }
+func func3(c chan int) { <-c }
+func func4(c chan int) { <-c }
+
+func TestGoroutineCounts(t *testing.T) {
+	c := make(chan int)
+	for i := 0; i < 100; i++ {
+		if i%10 == 0 {
+			go func1(c)
+			continue
+		}
+		if i%2 == 0 {
+			go func2(c)
+			continue
+		}
+		go func3(c)
+	}
+	time.Sleep(10 * time.Millisecond) // let goroutines block on channel
+
+	var w bytes.Buffer
+	Lookup("goroutine").WriteTo(&w, 1)
+	prof := w.String()
+
+	if !containsInOrder(prof, "\n50 @ ", "\n40 @", "\n10 @", "\n1 @") {
+		t.Errorf("expected sorted goroutine counts:\n%s", prof)
+	}
+
+	close(c)
+
+	time.Sleep(10 * time.Millisecond) // let goroutines exit
+}
+
+func containsInOrder(s string, all ...string) bool {
+	for _, t := range all {
+		i := strings.Index(s, t)
+		if i < 0 {
+			return false
+		}
+		s = s[i+len(t):]
+	}
+	return true
+}