[heap profiler] Add is_live field to AllocationProfile::Sample

IlyasShabi · V8 LUCI CQ · commit 0f024d4e66e0 · 2026-03-10T04:05:16.000-07:00
When using kSamplingIncludeObjectsCollectedByMajorGC/MinorGC flag, samples for collected objects are retained but callers had no way to distinguish live from dead objects. Add is_live to expose this information. Change-Id: I2e930644348ff942caa4b192a127c5baa05bbfef Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/7603535 Reviewed-by: Dominik Inführ <dinfuehr@chromium.org> Commit-Queue: Dominik Inführ <dinfuehr@chromium.org> Reviewed-by: Michael Lippautz <mlippautz@chromium.org> Cr-Commit-Position: refs/heads/main@{#105698}
diff --git a/AUTHORS b/AUTHORS
@@ -156,6 +156,7 @@ Huáng Jùnliàng <jlhwung@gmail.com>
 HyeockJin Kim <kherootz@gmail.com>
 Iain Ireland <iireland@mozilla.com>
 Ilya Gavrilin <ilya.gavrilin@syntacore.com>
+Ilyas Shabi <ilyasshabi94@gmail.com>
 Ingvar Stepanyan <me@rreverser.com>
 Ioseb Dzmanashvili <ioseb.dzmanashvili@gmail.com>
 Isiah Meadows <impinball@gmail.com>
diff --git a/include/v8-profiler.h b/include/v8-profiler.h
@@ -830,6 +830,12 @@ class V8_EXPORT AllocationProfile {
      * what samples were added or removed between two snapshots.
      */
     uint64_t sample_id;
+
+    /**
+     * Indicates whether the sampled allocation is still live or has already
+     * been collected by GC.
+     */
+    bool is_live;
   };
 
   /**
diff --git a/src/profiler/sampling-heap-profiler.cc b/src/profiler/sampling-heap-profiler.cc
@@ -312,9 +312,10 @@ SamplingHeapProfiler::BuildSamples() const {
   samples.reserve(samples_.size());
   for (const auto& it : samples_) {
     const Sample* sample = it.second.get();
+    const bool is_live = !sample->global.IsEmpty();
     samples.emplace_back(v8::AllocationProfile::Sample{
         sample->owner->id_, sample->size, ScaleSample(sample->size, 1).count,
-        sample->sample_id});
+        sample->sample_id, is_live});
   }
   return samples;
 }
diff --git a/test/cctest/test-heap-profiler.cc b/test/cctest/test-heap-profiler.cc
@@ -4324,6 +4324,82 @@ TEST(SamplingHeapProfilerLargeInterval) {
   heap_profiler->StopSamplingHeapProfiler();
 }
 
+TEST(SamplingHeapProfilerSampleWithoutGCFlags) {
+  v8::HandleScope scope(CcTest::isolate());
+  LocalContext env;
+  v8::HeapProfiler* heap_profiler = env.isolate()->GetHeapProfiler();
+
+  // Suppress randomness to avoid flakiness in tests.
+  i::v8_flags.sampling_heap_profiler_suppress_randomness = true;
+
+  heap_profiler->StartSamplingHeapProfiler(1024);
+
+  // Allocate objects that will be retained
+  CompileRun(
+      "var retained = [];\n"
+      "for (var i = 0; i < 500; i++) retained.push(new Array(10));\n");
+
+  CompileRun("for (var i = 0; i < 500; i++) new Array(10);\n");
+
+  std::unique_ptr<v8::AllocationProfile> profile(
+      heap_profiler->GetAllocationProfile());
+  CHECK(profile);
+
+  const auto& samples = profile->GetSamples();
+  CHECK(!samples.empty());
+
+  for (const auto& sample : samples) {
+    CHECK(sample.is_live);
+  }
+
+  heap_profiler->StopSamplingHeapProfiler();
+}
+
+TEST(SamplingHeapProfilerSampleIsLive) {
+  v8::HandleScope scope(CcTest::isolate());
+  LocalContext env;
+  v8::HeapProfiler* heap_profiler = env.isolate()->GetHeapProfiler();
+
+  // Suppress randomness to avoid flakiness in tests.
+  i::v8_flags.sampling_heap_profiler_suppress_randomness = true;
+
+  heap_profiler->StartSamplingHeapProfiler(
+      64, 16,
+      static_cast<v8::HeapProfiler::SamplingFlags>(
+          v8::HeapProfiler::kSamplingForceGC |
+          v8::HeapProfiler::kSamplingIncludeObjectsCollectedByMajorGC));
+
+  // Allocate objects that will be retained
+  CompileRun(
+      "var retained = [];\n"
+      "for (var i = 0; i < 500; i++) retained.push(new Array(10));\n");
+
+  CompileRun("for (var i = 0; i < 500; i++) new Array(10);\n");
+
+  std::unique_ptr<v8::AllocationProfile> profile(
+      heap_profiler->GetAllocationProfile());
+  CHECK(profile);
+
+  const auto& samples = profile->GetSamples();
+  CHECK(!samples.empty());
+
+  int live_samples = 0;
+  int dead_samples = 0;
+  for (const auto& sample : samples) {
+    if (sample.is_live) {
+      ++live_samples;
+    } else {
+      ++dead_samples;
+    }
+  }
+
+  // We expect both retained and collected allocations in this profile.
+  CHECK_GT(live_samples, 0);
+  CHECK_GT(dead_samples, 0);
+
+  heap_profiler->StopSamplingHeapProfiler();
+}
+
 TEST(HeapSnapshotPrototypeNotJSReceiver) {
   LocalContext env;
   v8::HandleScope scope(env.isolate());

-Original file line number
+Diff line change
 HyeockJin Kim <[email protected]>
 Iain Ireland <[email protected]>
 Ilya Gavrilin <[email protected]>
 +Ilyas Shabi <[email protected]>
 Ingvar Stepanyan <[email protected]>
 Ioseb Dzmanashvili <[email protected]>
 Isiah Meadows <[email protected]>
Original file line number	Diff line number	Diff line change
`@@ -312,9 +312,10 @@ SamplingHeapProfiler::BuildSamples() const {`
`312`	`312`	`samples.reserve(samples_.size());`
`313`	`313`	`for (const auto& it : samples_) {`
`314`	`314`	`const Sample* sample = it.second.get();`
	`315`	`+ const bool is_live = !sample->global.IsEmpty();`
`315`	`316`	`samples.emplace_back(v8::AllocationProfile::Sample{`
`316`	`317`	`sample->owner->id_, sample->size, ScaleSample(sample->size, 1).count,`
`317`		`- sample->sample_id});`
	`318`	`+ sample->sample_id, is_live});`
`318`	`319`	`}`
`319`	`320`	`return samples;`
`320`	`321`	`}`