code review 4031041: runtime/debug: new package

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.

[rsc, 2011/01/19 18:31:42]

s/()//

+// 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

[rsc, 2011/01/19 18:31:42]

s/()//

+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
+}