runtime/pprof: cpu profiling support

R=r, bradfitzgo, r2
CC=golang-dev
https://golang.org/cl/4313041

src/pkg/Makefile

@@ -184,7 +184,6 @@ NOTEST=\
 	net/dict\
 	rand\
 	runtime/cgo\
-	runtime/pprof\
 	syscall\
 	testing\
 	testing/iotest\

src/pkg/runtime/pprof/pprof.go

@@ -14,6 +14,7 @@ import (
 	"io"
 	"os"
 	"runtime"
+	"sync"
 )
 
 // WriteHeapProfile writes a pprof-formatted heap profile to w.
@@ -105,3 +106,71 @@ func WriteHeapProfile(w io.Writer) os.Error {
 	}
 	return b.Flush()
 }
+
+var cpu struct {
+	sync.Mutex
+	profiling bool
+	done      chan bool
+}
+
+// StartCPUProfile enables CPU profiling for the current process.
+// While profiling, the profile will be buffered and written to w.
+// StartCPUProfile returns an error if profiling is already enabled.
+func StartCPUProfile(w io.Writer) os.Error {
+	// The runtime routines allow a variable profiling rate,
+	// but in practice operating systems cannot trigger signals
+	// at more than about 500 Hz, and our processing of the
+	// signal is not cheap (mostly getting the stack trace).
+	// 100 Hz is a reasonable choice: it is frequent enough to
+	// produce useful data, rare enough not to bog down the
+	// system, and a nice round number to make it easy to
+	// convert sample counts to seconds.  Instead of requiring
+	// each client to specify the frequency, we hard code it.
+	const hz = 100
+
+	// Avoid queueing behind StopCPUProfile.
+	// Could use TryLock instead if we had it.
+	if cpu.profiling {
+		return fmt.Errorf("cpu profiling already in use")
+	}
+
+	cpu.Lock()
+	defer cpu.Unlock()
+	if cpu.done == nil {
+		cpu.done = make(chan bool)
+	}
+	// Double-check.
+	if cpu.profiling {
+		return fmt.Errorf("cpu profiling already in use")
+	}
+	cpu.profiling = true
+	runtime.SetCPUProfileRate(hz)
+	go profileWriter(w)
+	return nil
+}
+
+func profileWriter(w io.Writer) {
+	for {
+		data := runtime.CPUProfile()
+		if data == nil {
+			break
+		}
+		w.Write(data)
+	}
+	cpu.done <- true
+}
+
+// StopCPUProfile stops the current CPU profile, if any.
+// StopCPUProfile only returns after all the writes for the
+// profile have completed.
+func StopCPUProfile() {
+	cpu.Lock()
+	defer cpu.Unlock()
+
+	if !cpu.profiling {
+		return
+	}
+	cpu.profiling = false
+	runtime.SetCPUProfileRate(0)
+	<-cpu.done
+}

src/pkg/runtime/pprof/pprof_test.go

@@ -0,0 +1,69 @@
+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package pprof_test
+
+import (
+	"bytes"
+	"hash/crc32"
+	"runtime"
+	. "runtime/pprof"
+	"strings"
+	"testing"
+	"unsafe"
+)
+
+func TestCPUProfile(t *testing.T) {
+	if runtime.GOOS == "windows" || runtime.GOOS == "plan9" {
+		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)
+	}
+	StopCPUProfile()
+
+	// Convert []byte to []uintptr.
+	bytes := prof.Bytes()
+	val := *(*[]uintptr)(unsafe.Pointer(&bytes))
+	val = val[:len(bytes)/unsafe.Sizeof(uintptr(0))]
+
+	if len(val) < 10 {
+		t.Fatalf("profile too short: %#x", val)
+	}
+	if val[0] != 0 || val[1] != 3 || val[2] != 0 || val[3] != 1e6/100 || val[4] != 0 {
+		t.Fatalf("unexpected header %#x", val[:5])
+	}
+
+	// Check that profile is well formed and contains ChecksumIEEE.
+	found := false
+	val = val[5:]
+	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)
+		}
+		for _, pc := range val[2 : 2+val[1]] {
+			f := runtime.FuncForPC(pc)
+			if f == nil {
+				continue
+			}
+			if strings.Contains(f.Name(), "ChecksumIEEE") {
+				found = true
+			}
+		}
+		val = val[2+val[1]:]
+	}
+
+	if !found {
+		t.Fatal("did not find ChecksumIEEE in the profile")
+	}
+}