1 files changed, 96 insertions, 0 deletions
diff --git a/src/runtime/testdata/testprog/traceback_ancestors.go b/src/runtime/testdata/testprog/traceback_ancestors.go
new file mode 100644
index 0000000..8fc1aa7
--- /dev/null
+++ b/src/runtime/testdata/testprog/traceback_ancestors.go
@@ -0,0 +1,96 @@
+// 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 ")
+	var found bool
+	if buf, found = bytes.CutPrefix(buf, prefix); !found {
+		panic(fmt.Sprintf("expected %q at beginning of traceback:\n%s", prefix, buf))
+	}
+	id, _, _ := bytes.Cut(buf, []byte(" "))
+	return string(id)
+}