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runtime: soften up the GCTestIsReachable test a bit

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This test can fail due to objects being incorrectly retained due
to conservative scanning. Allow a bit of slop (1 accidentally
retained object) to prevent flaky failures.

Fixes #67204

"fixes" is a bit too strong a word. More like, hopefully reduces
the false positive rate to something approaching 0.

Change-Id: I09984f0cce50d8209aef19f3d89b0e295c86f8d1
Reviewed-on: https://go-review.googlesource.com/c/go/+/590615
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
This commit is contained in:
Keith Randall 2024-06-04 14:54:55 -07:00 committed by Keith Randall
parent 7274921681
commit 45967bb18e
1 changed files with 12 additions and 2 deletions
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14
src/runtime/gc_test.go
View file

@ -6,6 +6,7 @@ package runtime_test
import (
"fmt"
"math/bits"
"math/rand"
"os"
"reflect"
@ -278,8 +279,17 @@ func TestGCTestIsReachable(t *testing.T) {
}
got := runtime.GCTestIsReachable(all...)
if want != got {
t.Fatalf("did not get expected reachable set; want %b, got %b", want, got)
if got&want != want {
// This is a serious bug - an object is live (due to the KeepAlive
// call below), but isn't reported as such.
t.Fatalf("live object not in reachable set; want %b, got %b", want, got)
}
if bits.OnesCount64(got&^want) > 1 {
// Note: we can occasionally have a value that is retained even though
// it isn't live, due to conservative scanning of stack frames.
// See issue 67204. For now, we allow a "slop" of 1 unintentionally
// retained object.
t.Fatalf("dead object in reachable set; want %b, got %b", want, got)
}
runtime.KeepAlive(half)
}