Background finalization.

runtime/vm/scavenger.cc

Index: runtime/vm/scavenger.cc
diff --git a/runtime/vm/scavenger.cc b/runtime/vm/scavenger.cc
index 306a78a4978ac104cb62f3d870690a344235ff12..f68145990d582f609f570401a232c8630bebb2d9 100644
--- a/runtime/vm/scavenger.cc
+++ b/runtime/vm/scavenger.cc
@@ -193,10 +193,13 @@ class ScavengerVisitor : public ObjectPointerVisitor {
 
 class ScavengerWeakVisitor : public HandleVisitor {
  public:
-  explicit ScavengerWeakVisitor(Scavenger* scavenger)
-      :  HandleVisitor(Thread::Current()),
-         scavenger_(scavenger) {
-    ASSERT(scavenger->heap_->isolate() == Thread::Current()->isolate());
+  ScavengerWeakVisitor(Thread* thread,
+                       Scavenger* scavenger,
+                       FinalizationQueue* finalization_queue) :
+      HandleVisitor(thread),
+      scavenger_(scavenger),
+      queue_(finalization_queue) {
+    ASSERT(scavenger->heap_->isolate() == thread->isolate());
   }
 
   void VisitHandle(uword addr) {
@@ -204,7 +207,7 @@ class ScavengerWeakVisitor : public HandleVisitor {
       reinterpret_cast<FinalizablePersistentHandle*>(addr);
     RawObject** p = handle->raw_addr();
     if (scavenger_->IsUnreachable(p)) {
-      handle->UpdateUnreachable(thread()->isolate());
+      handle->UpdateUnreachable(thread()->isolate(), queue_);
     } else {
       handle->UpdateRelocated(thread()->isolate());
     }
@@ -212,6 +215,7 @@ class ScavengerWeakVisitor : public HandleVisitor {
 
  private:
   Scavenger* scavenger_;
+  FinalizationQueue* queue_;
 
   DISALLOW_COPY_AND_ASSIGN(ScavengerWeakVisitor);
 };
@@ -812,8 +816,14 @@ void Scavenger::Scavenge(bool invoke_api_callbacks) {
     int64_t middle = OS::GetCurrentTimeMicros();
     {
       TIMELINE_FUNCTION_GC_DURATION(thread, "WeakHandleProcessing");
-      ScavengerWeakVisitor weak_visitor(this);
+      FinalizationQueue* queue = new FinalizationQueue();
+      ScavengerWeakVisitor weak_visitor(thread, this, queue);
       IterateWeakRoots(isolate, &weak_visitor);
+      if (queue->length() > 0) {
+        Dart::thread_pool()->Run(new BackgroundFinalizer(isolate, queue));
+      } else {
+        delete queue;
+      }
     }
     ProcessWeakReferences();
     page_space->ReleaseDataLock();