Use atomic sequence for sample trace ids
I noticed the current approach yielded collisions in the generated
sample trace ids on events with close timestamps, likely due to a
loss of precision in the way the hash seeds are casted and combined
In any case, for the sake of simplicity and performance (given the cost
of obtaining a timestamp with base::TimeTicks::now()) this implements
a helper that computes a trace id based on an atomic sequential number.
Bug: 390155857
Change-Id: I87969a7be30f30001655c63c8d93b49ad8158a00
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/6227576
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Andres Olivares <andoli@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/main@{#98566}
diff --git a/BUILD.bazel b/BUILD.bazel
index 631cb5c0..5065af7 100644
--- a/BUILD.bazel
+++ b/BUILD.bazel
@@ -2489,6 +2489,7 @@
"src/tracing/trace-event.cc",
"src/tracing/trace-event.h",
"src/tracing/trace-event-no-perfetto.h",
+ "src/tracing/trace-id.h",
"src/tracing/traced-value.cc",
"src/tracing/traced-value.h",
"src/tracing/tracing-category-observer.cc",
diff --git a/BUILD.gn b/BUILD.gn
index 7ad7e11..ef1d419 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -4212,6 +4212,7 @@
"src/torque/runtime-macro-shims.h",
"src/tracing/trace-event-no-perfetto.h",
"src/tracing/trace-event.h",
+ "src/tracing/trace-id.h",
"src/tracing/traced-value.h",
"src/tracing/tracing-category-observer.h",
"src/utils/address-map.h",
diff --git a/src/inspector/v8-console.cc b/src/inspector/v8-console.cc
index fcc6ed9..ba504ff 100644
--- a/src/inspector/v8-console.cc
+++ b/src/inspector/v8-console.cc
@@ -26,6 +26,7 @@
#include "src/inspector/v8-stack-trace-impl.h"
#include "src/inspector/v8-value-utils.h"
#include "src/tracing/trace-event.h"
+#include "src/tracing/trace-id.h"
namespace v8_inspector {
@@ -461,16 +462,10 @@
TRACE_EVENT(TRACE_DISABLED_BY_DEFAULT("v8.inspector"), "V8Console::TimeStamp",
"data", ([&](perfetto::TracedValue context) {
auto dict = std::move(context).WriteDictionary();
-
- uint64_t name_hash =
- std::hash<std::string>{}("V8Console::TimeStamp");
- uint64_t timestamp_hash = std::hash<uint64_t>{}(
- v8::base::TimeTicks::Now().ToInternalValue());
- uint64_t hash =
- v8::base::hash_combine(name_hash, timestamp_hash);
+ uint64_t trace_id = v8::tracing::TraceId();
v8::CpuProfiler::CpuProfiler::CollectSample(
- m_inspector->isolate(), hash);
- dict.Add("sampleTraceId", hash);
+ m_inspector->isolate(), trace_id);
+ dict.Add("sampleTraceId", trace_id);
static const char* kNames[] = {"name", "start", "end",
"track", "trackGroup", "color"};
for (int i = 0; i < info.Length() &&
@@ -570,19 +565,14 @@
m_inspector->asyncTaskStarted(taskInfo->Id());
{
#ifdef V8_USE_PERFETTO
- TRACE_EVENT(
- TRACE_DISABLED_BY_DEFAULT("v8.inspector"), "V8Console::runTask", "data",
- ([&](perfetto::TracedValue context) {
- auto dict = std::move(context).WriteDictionary();
- uint64_t task_id_hash =
- std::hash<uint64_t>{}(reinterpret_cast<uint64_t>(taskInfo->Id()));
- uint64_t timestamp_hash = std::hash<uint64_t>{}(
- v8::base::TimeTicks::Now().ToInternalValue());
- uint64_t hash = v8::base::hash_combine(task_id_hash, timestamp_hash);
-
- v8::CpuProfiler::CpuProfiler::CollectSample(isolate, hash);
- dict.Add("sampleTraceId", hash);
- }));
+ TRACE_EVENT(TRACE_DISABLED_BY_DEFAULT("v8.inspector"), "V8Console::runTask",
+ "data", ([&](perfetto::TracedValue context) {
+ uint64_t trace_id = v8::tracing::TraceId();
+ auto dict = std::move(context).WriteDictionary();
+ v8::CpuProfiler::CpuProfiler::CollectSample(isolate,
+ trace_id);
+ dict.Add("sampleTraceId", trace_id);
+ }));
#endif // V8_USE_PERFETTO
v8::Local<v8::Value> result;
diff --git a/src/tracing/trace-id.h b/src/tracing/trace-id.h
new file mode 100644
index 0000000..f594340
--- /dev/null
+++ b/src/tracing/trace-id.h
@@ -0,0 +1,19 @@
+// Copyright 2025 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_TRACING_TRACE_ID_H_
+#define V8_TRACING_TRACE_ID_H_
+
+#include "src/base/platform/platform.h"
+
+namespace v8 {
+namespace tracing {
+V8_INLINE uint64_t TraceId() {
+ static std::atomic<uint64_t> sequence_number(0);
+ return sequence_number.fetch_add(1, std::memory_order_relaxed);
+}
+} // namespace tracing
+} // namespace v8
+
+#endif // V8_TRACING_TRACE_ID_H_
