runtime/traceback: support tracking goroutine ancestor tracebacks with GODEBUG="tracebackancestors=N"

Currently, collecting a stack trace via runtime.Stack captures the stack for the
immediately running goroutines. This change extends those tracebacks to include
the tracebacks of their ancestors. This is done with a low memory cost and only
utilized when debug option tracebackancestors is set to a value greater than 0.

Resolves #22289

Change-Id: I7edacc62b2ee3bd278600c4a21052c351f313f3a
Reviewed-on: https://go-review.googlesource.com/70993
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

1 files changed, 40 insertions, 0 deletions

diff --git a/src/runtime/stack_test.go b/src/runtime/stack_test.go
index 8342724d0b..91d10bad5c 100644
--- a/src/runtime/stack_test.go
+++ b/src/runtime/stack_test.go
@@ -8,6 +8,7 @@ import (
 	"bytes"
 	"fmt"
 	"reflect"
+	"regexp"
 	. "runtime"
 	"strings"
 	"sync"
@@ -696,3 +697,42 @@ func TestTracebackSystemstack(t *testing.T) {
 		t.Fatalf("expected 5 calls to TracebackSystemstack and 1 call to TestTracebackSystemstack, got:%s", tb.String())
 	}
 }
+
+func TestTracebackAncestors(t *testing.T) {
+	goroutineRegex := regexp.MustCompile(`goroutine [0-9]+ \[`)
+	for _, tracebackDepth := range []int{0, 1, 5, 50} {
+		output := runTestProg(t, "testprog", "TracebackAncestors", fmt.Sprintf("GODEBUG=tracebackancestors=%d", tracebackDepth))
+
+		numGoroutines := 3
+		numFrames := 2
+		ancestorsExpected := numGoroutines
+		if numGoroutines > tracebackDepth {
+			ancestorsExpected = tracebackDepth
+		}
+
+		matches := goroutineRegex.FindAllStringSubmatch(output, -1)
+		if len(matches) != 2 {
+			t.Fatalf("want 2 goroutines, got:\n%s", output)
+		}
+
+		// Check functions in the traceback.
+		fns := []string{"main.recurseThenCallGo", "main.main", "main.printStack", "main.TracebackAncestors"}
+		for _, fn := range fns {
+			if !strings.Contains(output, "\n"+fn+"(") {
+				t.Fatalf("expected %q function in traceback:\n%s", fn, output)
+			}
+		}
+
+		if want, count := "originating from goroutine", ancestorsExpected; strings.Count(output, want) != count {
+			t.Errorf("output does not contain %d instances of %q:\n%s", count, want, output)
+		}
+
+		if want, count := "main.recurseThenCallGo(...)", ancestorsExpected*(numFrames+1); strings.Count(output, want) != count {
+			t.Errorf("output does not contain %d instances of %q:\n%s", count, want, output)
+		}
+
+		if want, count := "main.recurseThenCallGo(0x", 1; strings.Count(output, want) != count {
+			t.Errorf("output does not contain %d instances of %q:\n%s", count, want, output)
+		}
+	}
+}