Prepares allocation for proper sync with mutator and bg threads.

runtime/vm/heap.cc

Index: runtime/vm/heap.cc
diff --git a/runtime/vm/heap.cc b/runtime/vm/heap.cc
index eccf14fe5827583fa16be668d843e1e80dd5a389..882436724e7f5ea4464dd26ec752a0d13f27ca6d 100644
--- a/runtime/vm/heap.cc
+++ b/runtime/vm/heap.cc
@@ -57,7 +57,7 @@ Heap::~Heap() {
   }
 }
 
-void Heap::AbandonRemainingTLAB(Thread* thread) {
+void Heap::MakeTLABIterable(Thread* thread) {
   uword start = thread->top();
   uword end = thread->end();
   ASSERT(end >= start);
@@ -69,8 +69,11 @@ void Heap::AbandonRemainingTLAB(Thread* thread) {
   if (size >= kObjectAlignment) {
     FreeListElement::AsElement(start, size);
     ASSERT(RawObject::FromAddr(start)->Size() == size);
-    ASSERT((start + size) == new_space_.top());
   }
+}
+
+void Heap::AbandonRemainingTLAB(Thread* thread) {
+  MakeTLABIterable(thread);
   thread->set_top(0);
   thread->set_end(0);
 }
@@ -96,11 +99,14 @@ uword Heap::AllocateNew(intptr_t size) {
   }
 
   AbandonRemainingTLAB(thread);
+
+  // TODO(danunez): Lock for new space here
   if (tlab_size > 0) {
     uword tlab_top = new_space_.TryAllocateNewTLAB(thread, tlab_size);
     if (tlab_top != 0) {
       addr = new_space_.TryAllocateInTLAB(thread, size);
       ASSERT(addr != 0);
+      // TODO(danunez): Unlock for new space here
       return addr;
     }
   }
@@ -110,9 +116,16 @@ uword Heap::AllocateNew(intptr_t size) {
   // This call to CollectGarbage might end up "reusing" a collection spawned
   // from a different thread and will be racing to allocate the requested
   // memory with other threads being released after the collection.
+
+  // TODO(danunez): Ensure that once we start collecting garbage, everything
+  // stops allocating.
+  // Safepoint should be dealing with this, but we need to make sure somehow.
   CollectGarbage(kNew);
   tlab_size = CalculateTLABSize();
   uword tlab_top = new_space_.TryAllocateNewTLAB(thread, tlab_size);
+
+  // TODO(danunez): Unlock for new space here. Regardless of the outcome, we
+  // don't need the new space.
   if (tlab_top != 0) {
     addr = new_space_.TryAllocateInTLAB(thread, size);
     // It is possible a GC doesn't clear enough space.
@@ -603,14 +616,14 @@ bool Heap::VerifyGC(MarkExpectation mark_expectation) const {
   StackZone stack_zone(Thread::Current());
 
   // Change the new space's top_ with the more up-to-date thread's view of top_
-  uword saved_top = new_space_.FlushTLS();
+  new_space_.FlushTLS();
 
   ObjectSet* allocated_set =
       CreateAllocatedObjectSet(stack_zone.GetZone(), mark_expectation);
   VerifyPointersVisitor visitor(isolate(), allocated_set);
+  // TODO(danunez): Need to lock and unlock for new space here.
   VisitObjectPointers(&visitor);
 
-  new_space_.UnflushTLS(saved_top);
   // Only returning a value so that Heap::Validate can be called from an ASSERT.
   return true;
 }