From: Michael Anthony Knyszek <mknyszek@google.com>
Date: Wed, 21 May 2025 17:50:15 +0000 (+0000)
Subject: internal/trace: skip clock snapshot checks on Windows in stress mode
X-Git-Tag: go1.25rc1~139
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=77345f41ee36c8db3ba7e0f687a8834fa7b83c48;p=gostls13.git

internal/trace: skip clock snapshot checks on Windows in stress mode

Windows' monotonic and wall clock granularity is just too coarse to get
reasonable values out of stress mode, which is creating new trace
generations constantly.

Fixes #73813.

Change-Id: Id9cb2fed9775ce8d78a736d0164daa7bf45075e0
Reviewed-on: https://go-review.googlesource.com/c/go/+/675096
Reviewed-by: Felix Geisendörfer <felix.geisendoerfer@datadoghq.com>
Reviewed-by: Roland Shoemaker <roland@golang.org>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
---

diff --git a/src/internal/trace/reader_test.go b/src/internal/trace/reader_test.go
index 222d2dfa82..691cda6688 100644
--- a/src/internal/trace/reader_test.go
+++ b/src/internal/trace/reader_test.go
@@ -42,7 +42,9 @@ func TestReaderGolden(t *testing.T) {
 			if err != nil {
 				t.Fatalf("failed to parse test file at %s: %v", testPath, err)
 			}
-			testReader(t, tr, ver, exp)
+			v := testtrace.NewValidator()
+			v.GoVersion = ver
+			testReader(t, tr, v, exp)
 		})
 	}
 }
@@ -94,7 +96,7 @@ func FuzzReader(f *testing.F) {
 	})
 }
 
-func testReader(t *testing.T, tr io.Reader, ver version.Version, exp *testtrace.Expectation) {
+func testReader(t *testing.T, tr io.Reader, v *testtrace.Validator, exp *testtrace.Expectation) {
 	r, err := trace.NewReader(tr)
 	if err != nil {
 		if err := exp.Check(err); err != nil {
@@ -102,8 +104,6 @@ func testReader(t *testing.T, tr io.Reader, ver version.Version, exp *testtrace.
 		}
 		return
 	}
-	v := testtrace.NewValidator()
-	v.GoVersion = ver
 	for {
 		ev, err := r.ReadEvent()
 		if err == io.EOF {
diff --git a/src/internal/trace/testtrace/validation.go b/src/internal/trace/testtrace/validation.go
index da0e871287..2060d0d44c 100644
--- a/src/internal/trace/testtrace/validation.go
+++ b/src/internal/trace/testtrace/validation.go
@@ -23,6 +23,9 @@ type Validator struct {
 	tasks     map[trace.TaskID]string
 	lastSync  trace.Sync
 	GoVersion version.Version
+
+	// Flags to modify validation behavior.
+	skipClockSnapshotChecks bool // Some platforms can't guarantee a monotonically increasing clock reading.
 }
 
 type schedContext struct {
@@ -53,6 +56,14 @@ func NewValidator() *Validator {
 	}
 }
 
+// SkipClockSnapshotChecks causes the validator to skip checks on the clock snapshots.
+//
+// Some platforms like Windows, with a small enough trace period, are unable to produce
+// monotonically increasing timestamps due to very coarse clock granularity.
+func (v *Validator) SkipClockSnapshotChecks() {
+	v.skipClockSnapshotChecks = true
+}
+
 // Event validates ev as the next event in a stream of trace.Events.
 //
 // Returns an error if validation fails.
@@ -97,14 +108,16 @@ func (v *Validator) Event(ev trace.Event) error {
 			if s.ClockSnapshot.Trace == 0 {
 				e.Errorf("sync %d has zero trace time", s.N)
 			}
-			if s.N >= 2 && !s.ClockSnapshot.Wall.After(v.lastSync.ClockSnapshot.Wall) {
-				e.Errorf("sync %d has non-increasing wall time: %v vs %v", s.N, s.ClockSnapshot.Wall, v.lastSync.ClockSnapshot.Wall)
-			}
-			if s.N >= 2 && !(s.ClockSnapshot.Mono > v.lastSync.ClockSnapshot.Mono) {
-				e.Errorf("sync %d has non-increasing mono time: %v vs %v", s.N, s.ClockSnapshot.Mono, v.lastSync.ClockSnapshot.Mono)
-			}
-			if s.N >= 2 && !(s.ClockSnapshot.Trace > v.lastSync.ClockSnapshot.Trace) {
-				e.Errorf("sync %d has non-increasing trace time: %v vs %v", s.N, s.ClockSnapshot.Trace, v.lastSync.ClockSnapshot.Trace)
+			if !v.skipClockSnapshotChecks {
+				if s.N >= 2 && !s.ClockSnapshot.Wall.After(v.lastSync.ClockSnapshot.Wall) {
+					e.Errorf("sync %d has non-increasing wall time: %v vs %v", s.N, s.ClockSnapshot.Wall, v.lastSync.ClockSnapshot.Wall)
+				}
+				if s.N >= 2 && !(s.ClockSnapshot.Mono > v.lastSync.ClockSnapshot.Mono) {
+					e.Errorf("sync %d has non-increasing mono time: %v vs %v", s.N, s.ClockSnapshot.Mono, v.lastSync.ClockSnapshot.Mono)
+				}
+				if s.N >= 2 && !(s.ClockSnapshot.Trace > v.lastSync.ClockSnapshot.Trace) {
+					e.Errorf("sync %d has non-increasing trace time: %v vs %v", s.N, s.ClockSnapshot.Trace, v.lastSync.ClockSnapshot.Trace)
+				}
 			}
 		}
 		v.lastSync = s
diff --git a/src/internal/trace/trace_test.go b/src/internal/trace/trace_test.go
index 8c40e84a81..0aa297d762 100644
--- a/src/internal/trace/trace_test.go
+++ b/src/internal/trace/trace_test.go
@@ -618,7 +618,16 @@ func testTraceProg(t *testing.T, progName string, extra func(t *testing.T, trace
 		tb := traceBuf.Bytes()
 
 		// Test the trace and the parser.
-		testReader(t, bytes.NewReader(tb), version.Current, testtrace.ExpectSuccess())
+		v := testtrace.NewValidator()
+		v.GoVersion = version.Current
+		if runtime.GOOS == "windows" && stress {
+			// Under stress mode we're constantly advancing trace generations.
+			// Windows' clock granularity is too coarse to guarantee monotonic
+			// timestamps for monotonic and wall clock time in this case, so
+			// skip the checks.
+			v.SkipClockSnapshotChecks()
+		}
+		testReader(t, bytes.NewReader(tb), v, testtrace.ExpectSuccess())
 
 		// Run some extra validation.
 		if !t.Failed() && extra != nil {