[vm] Avoid data race during Dart_IsolateGroupHeapNewUsedMetric.

Precise new-space usage requires looking at all the TLAB pointers and normally only occurs under a GC safepoint. For external queries coarsen the answer to capacity. TEST=g3 Bug: b/324221135 Change-Id: I0e83bbcddba21ddf539fb2afdedf2959cef2c078 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/352682 Reviewed-by: Siva Annamalai <[email protected]> Commit-Queue: Ryan Macnak <[email protected]>
dart-lang · Feb 14, 2024 · a407280 · a407280
1 parent 974dfa3
commit a407280
Showing 1 changed file with 4 additions and 1 deletion.
diff --git a/runtime/vm/metrics.cc b/runtime/vm/metrics.cc
@@ -158,7 +158,10 @@ int64_t MetricHeapOldExternal::Value() const {
 
 int64_t MetricHeapNewUsed::Value() const {
   ASSERT(isolate_group() == IsolateGroup::Current());
-  return isolate_group()->heap()->UsedInWords(Heap::kNew) * kWordSize;
+  // UsedInWords requires a safepoint to access all the TLAB pointers without a
+  // data race, so coarsen this metric to capacity. Preferable to locking during
+  // new-space allocation.
+  return isolate_group()->heap()->CapacityInWords(Heap::kNew) * kWordSize;
 }
 
 int64_t MetricHeapNewCapacity::Value() const {