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// Copyright 2018 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 main
import (
"bytes"
"fmt"
"runtime"
"strings"
)
func init() {
register("TracebackAncestors", TracebackAncestors)
}
const numGoroutines = 3
const numFrames = 2
func TracebackAncestors() {
w := make(chan struct{})
recurseThenCallGo(w, numGoroutines, numFrames, true)
<-w
printStack()
close(w)
}
var ignoreGoroutines = make(map[string]bool)
func printStack() {
buf := make([]byte, 1024)
for {
n := runtime.Stack(buf, true)
if n < len(buf) {
all := string(buf[:n])
var saved string
// Delete any ignored goroutines, if present.
for all != "" {
var g string
g, all, _ = strings.Cut(all, "\n\n")
if strings.HasPrefix(g, "goroutine ") {
id, _, _ := strings.Cut(strings.TrimPrefix(g, "goroutine "), " ")
if ignoreGoroutines[id] {
continue
}
}
if saved != "" {
saved += "\n\n"
}
saved += g
}
fmt.Print(saved)
return
}
buf = make([]byte, 2*len(buf))
}
}
func recurseThenCallGo(w chan struct{}, frames int, goroutines int, main bool) {
if frames == 0 {
// Signal to TracebackAncestors that we are done recursing and starting goroutines.
w <- struct{}{}
<-w
return
}
if goroutines == 0 {
// Record which goroutine this is so we can ignore it
// in the traceback if it hasn't finished exiting by
// the time we printStack.
if !main {
ignoreGoroutines[goroutineID()] = true
}
// Start the next goroutine now that there are no more recursions left
// for this current goroutine.
go recurseThenCallGo(w, frames-1, numFrames, false)
return
}
recurseThenCallGo(w, frames, goroutines-1, main)
}
func goroutineID() string {
buf := make([]byte, 128)
runtime.Stack(buf, false)
prefix := []byte("goroutine ")
if !bytes.HasPrefix(buf, prefix) {
panic(fmt.Sprintf("expected %q at beginning of traceback:\n%s", prefix, buf))
}
id, _, _ := bytes.Cut(bytes.TrimPrefix(buf, prefix), []byte(" "))
return string(id)
}
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