runtime/debug: new package

Facilities for printing stack traces from within a running goroutine.

R=rsc
CC=golang-dev
https://golang.org/cl/4031041

src/pkg/Makefile

@@ -113,6 +113,7 @@ DIRS=\
 	rpc/jsonrpc\
 	runtime\
 	runtime/cgo\
+	runtime/debug\
 	runtime/pprof\
 	scanner\
 	smtp\

src/pkg/runtime/debug/stack.go

+// 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.
+
+// The debug package contains facilities for programs to debug themselves
+// while they are running.
+package debug
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"runtime"
+)
+
+var (
+	dunno     = []byte("???")
+	centerDot = []byte("·")
+	dot       = []byte(".")
+)
+
+// PrintStack prints to standard error the stack trace returned by Stack.
+func PrintStack() {
+	os.Stderr.Write(stack())
+}
+
+// Stack returns a formatted stack trace of the goroutine that calls it.
+// For each routine, it includes the source line information and PC value,
+// then attempts to discover, for Go functions, the calling function or
+// method and the text of the line containing the invocation.
+func Stack() []byte {
+	return stack()
+}
+
+// stack implements Stack, skipping 2 frames
+func stack() []byte {
+	buf := new(bytes.Buffer) // the returned data
+	// As we loop, we open files and read them. These variables record the currently
+	// loaded file.
+	var lines [][]byte
+	var lastFile string
+	for i := 2; ; i++ { // Caller we care about is the user, 2 frames up
+		pc, file, line, ok := runtime.Caller(i)
+		if !ok {
+			break
+		}
+		// Print this much at least.  If we can't find the source, it won't show.
+		fmt.Fprintf(buf, "%s:%d (0x%x)\n", file, line, pc)
+		if file != lastFile {
+			data, err := ioutil.ReadFile(file)
+			if err != nil {
+				continue
+			}
+			lines = bytes.Split(data, []byte{'\n'}, -1)
+			lastFile = file
+		}
+		line-- // in stack trace, lines are 1-indexed but our array is 0-indexed
+		fmt.Fprintf(buf, "\t%s: %s\n", function(pc), source(lines, line))
+	}
+	return buf.Bytes()
+}
+
+// source returns a space-trimmed slice of the n'th line.
+func source(lines [][]byte, n int) []byte {
+	if n < 0 || n >= len(lines) {
+		return dunno
+	}
+	return bytes.Trim(lines[n], " \t")
+}
+
+// function returns, if possible, the name of the function containing the PC.
+func function(pc uintptr) []byte {
+	fn := runtime.FuncForPC(pc)
+	if fn == nil {
+		return dunno
+	}
+	name := []byte(fn.Name())
+	// The name includes the path name to the package, which is unnecessary
+	// since the file name is already included.  Plus, it has center dots.
+	// That is, we see
+	//	runtime/debug.*T·ptrmethod
+	// and want
+	//	*T.ptrmethod
+	if period := bytes.Index(name, dot); period >= 0 {
+		name = name[period+1:]
+	}
+	name = bytes.Replace(name, centerDot, dot, -1)
+	return name
+}

src/pkg/runtime/debug/stack_test.go

+// 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 debug
+
+import (
+	"strings"
+	"testing"
+)
+
+type T int
+
+func (t *T) ptrmethod() []byte {
+	return Stack()
+}
+func (t T) method() []byte {
+	return t.ptrmethod()
+}
+
+/*
+	The traceback should look something like this, modulo line numbers and hex constants.
+	Don't worry much about the base levels, but check the ones in our own package.
+
+		/Users/r/go/src/pkg/runtime/debug/stack_test.go:15 (0x13878)
+			*T.ptrmethod: return Stack()
+		/Users/r/go/src/pkg/runtime/debug/stack_test.go:18 (0x138dd)
+			T.method: return t.ptrmethod()
+		/Users/r/go/src/pkg/runtime/debug/stack_test.go:23 (0x13920)
+			TestStack: b := T(0).method()
+		/Users/r/go/src/pkg/testing/testing.go:132 (0x14a7a)
+			tRunner: test.F(t)
+		/Users/r/go/src/pkg/runtime/proc.c:145 (0xc970)
+			???: runtime·unlock(&runtime·sched);
+*/
+func TestStack(t *testing.T) {
+	b := T(0).method()
+	lines := strings.Split(string(b), "\n", -1)
+	if len(lines) <= 6 {
+		t.Fatal("too few lines")
+	}
+	check(t, lines[0], "src/pkg/runtime/debug/stack_test.go")
+	check(t, lines[1], "\t*T.ptrmethod: return Stack()")
+	check(t, lines[2], "src/pkg/runtime/debug/stack_test.go")
+	check(t, lines[3], "\tT.method: return t.ptrmethod()")
+	check(t, lines[4], "src/pkg/runtime/debug/stack_test.go")
+	check(t, lines[5], "\tTestStack: b := T(0).method()")
+	check(t, lines[6], "src/pkg/testing/testing.go")
+}
+
+func check(t *testing.T, line, has string) {
+	if strings.Index(line, has) < 0 {
+		t.Errorf("expected %q in %q", has, line)
+	}
+}