Prevent race between GC and interrupts from other threads.

src/heap.cc

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@@ skipping 6063 matching lines @@
   if (mode != VISIT_ALL_IN_SCAVENGE &&
       mode != VISIT_ALL_IN_SWEEP_NEWSPACE) {
     // Scavenge collections have special processing for this.
     external_string_table_.Iterate(v);
   }
   v->Synchronize(VisitorSynchronization::kExternalStringsTable);
 }
 
 
 void Heap::IterateStrongRoots(ObjectVisitor* v, VisitMode mode) {
-  v->VisitPointers(&roots_[0], &roots_[kStrongRootListLength]);
+  { // Avoid race with interrupts that set the stack limit on the root list.
+    // Note that GC does not actually care about the value of the stack limit
+    // as long as it is a smi.  We may want to revisit this if this causes
+    // performance regressions by blocking the optimizing compiler thread.
+    ExecutionAccess access(isolate());

[Michael Starzinger, 2014/02/07 10:24:50]

As discussed offline: This seems very much like a redundant lock to me. I know
the motivation is to make TSAN happy, but I have issues with taking a lock in
IterateStringRoots, especially for a field that is _always_ a SMI.

One suggestion from my end would be to reorder the strong roots list in a way
that groups SMIs at the end so that the GC doesn't need to look at them at all.

+    v->VisitPointers(&roots_[0], &roots_[kStrongRootListLength]);
+  }
   v->Synchronize(VisitorSynchronization::kStrongRootList);
 
   v->VisitPointer(BitCast<Object**>(&hidden_string_));
   v->Synchronize(VisitorSynchronization::kInternalizedString);
 
   isolate_->bootstrapper()->Iterate(v);
   v->Synchronize(VisitorSynchronization::kBootstrapper);
   isolate_->Iterate(v);
   v->Synchronize(VisitorSynchronization::kTop);
   Relocatable::Iterate(isolate_, v);
@@ skipping 1567 matching lines @@
       static_cast<int>(object_sizes_last_time_[index]));
   CODE_AGE_LIST_COMPLETE(ADJUST_LAST_TIME_OBJECT_COUNT)
 #undef ADJUST_LAST_TIME_OBJECT_COUNT
 
   OS::MemCopy(object_counts_last_time_, object_counts_, sizeof(object_counts_));
   OS::MemCopy(object_sizes_last_time_, object_sizes_, sizeof(object_sizes_));
   ClearObjectStats();
 }
 
 } }  // namespace v8::internal