runtime/pprof: test multithreaded profile, remove OS X workarounds

This means that pprof will no longer report profiles on OS X.
That's unfortunate, but the profiles were often wrong and, worse,
it was difficult to tell whether the profile was wrong or not.

The workarounds were making the scheduler more complex,
possibly caused a deadlock (see issue 5519), and did not actually
deliver reliable results.

It may be possible for adventurous users to apply a patch to
their kernels to get working results, or perhaps having no results
will encourage someone to do the work of creating a profiling
thread like on Windows. Issue 6047 has details.

Fixes #5519.
Fixes #6047.

R=golang-dev, bradfitz, r
CC=golang-dev
https://golang.org/cl/12429045

src/pkg/runtime/pprof/pprof_test.go

@@ -19,6 +19,38 @@ import (
 )
 
 func TestCPUProfile(t *testing.T) {
+	buf := make([]byte, 100000)
+	testCPUProfile(t, []string{"crc32.ChecksumIEEE"}, func() {
+		// This loop takes about a quarter second on a 2 GHz laptop.
+		// We only need to get one 100 Hz clock tick, so we've got
+		// a 25x safety buffer.
+		for i := 0; i < 1000; i++ {
+			crc32.ChecksumIEEE(buf)
+		}
+	})
+}
+
+func TestCPUProfileMultithreaded(t *testing.T) {
+	buf := make([]byte, 100000)
+	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(2))
+	testCPUProfile(t, []string{"crc32.ChecksumIEEE", "crc32.Update"}, func() {
+		c := make(chan int)
+		go func() {
+			for i := 0; i < 2000; i++ {
+				crc32.Update(0, crc32.IEEETable, buf)
+			}
+			c <- 1
+		}()
+		// This loop takes about a quarter second on a 2 GHz laptop.
+		// We only need to get one 100 Hz clock tick, so we've got
+		// a 25x safety buffer.
+		for i := 0; i < 2000; i++ {
+			crc32.ChecksumIEEE(buf)
+		}
+	})
+}
+
+func testCPUProfile(t *testing.T, need []string, f func()) {
 	switch runtime.GOOS {
 	case "darwin":
 		out, err := exec.Command("uname", "-a").CombinedOutput()
@@ -27,26 +59,16 @@ func TestCPUProfile(t *testing.T) {
 		}
 		vers := string(out)
 		t.Logf("uname -a: %v", vers)
-		// Lion uses "Darwin Kernel Version 11".
-		if strings.Contains(vers, "Darwin Kernel Version 10") && strings.Contains(vers, "RELEASE_X86_64") {
-			t.Skip("skipping test on known-broken kernel (64-bit Leopard / Snow Leopard)")
-		}
 	case "plan9":
 		// unimplemented
 		return
 	}
 
-	buf := make([]byte, 100000)
 	var prof bytes.Buffer
 	if err := StartCPUProfile(&prof); err != nil {
 		t.Fatal(err)
 	}
-	// This loop takes about a quarter second on a 2 GHz laptop.
-	// We only need to get one 100 Hz clock tick, so we've got
-	// a 25x safety buffer.
-	for i := 0; i < 1000; i++ {
-		crc32.ChecksumIEEE(buf)
-	}
+	f()
 	StopCPUProfile()
 
 	// Convert []byte to []uintptr.
@@ -56,6 +78,10 @@ func TestCPUProfile(t *testing.T) {
 	val = val[:l]
 
 	if l < 13 {
+		if runtime.GOOS == "darwin" {
+			t.Logf("ignoring failure on OS X; see golang.org/issue/6047")
+			return
+		}
 		t.Fatalf("profile too short: %#x", val)
 	}
 
@@ -69,7 +95,7 @@ func TestCPUProfile(t *testing.T) {
 	}
 
 	// Check that profile is well formed and contains ChecksumIEEE.
-	found := false
+	have := make([]uintptr, len(need))
 	for len(val) > 0 {
 		if len(val) < 2 || val[0] < 1 || val[1] < 1 || uintptr(len(val)) < 2+val[1] {
 			t.Fatalf("malformed profile.  leftover: %#x", val)
@@ -79,14 +105,38 @@ func TestCPUProfile(t *testing.T) {
 			if f == nil {
 				continue
 			}
-			if strings.Contains(f.Name(), "ChecksumIEEE") {
-				found = true
+			for i, name := range need {
+				if strings.Contains(f.Name(), name) {
+					have[i] += val[0]
+				}
 			}
 		}
 		val = val[2+val[1]:]
 	}
 
-	if !found {
-		t.Fatal("did not find ChecksumIEEE in the profile")
+	var total uintptr
+	for i, name := range need {
+		total += have[i]
+		t.Logf("%s: %d\n", name, have[i])
+	}
+	ok := true
+	if total == 0 {
+		t.Logf("no CPU profile samples collected")
+		ok = false
+	}
+	min := total / uintptr(len(have)) / 2
+	for i, name := range need {
+		if have[i] < min {
+			t.Logf("%s has %d samples out of %d, want at least %d, ideally %d", name, have[i], total, min, total/uintptr(len(have)))
+			ok = false
+		}
+	}
+
+	if !ok {
+		if runtime.GOOS == "darwin" {
+			t.Logf("ignoring failure on OS X; see golang.org/issue/6047")
+			return
+		}
+		t.FailNow()
 	}
 }