Changes new space allocation from simple bump pointer allocation from

runtime/vm/isolate.cc

Index: runtime/vm/isolate.cc
diff --git a/runtime/vm/isolate.cc b/runtime/vm/isolate.cc
index c8f8ff2227e514e23e6556dc92699c36ad82502d..76b50ab1971efbc1c15d2d36a6b41e5dc1f7b732 100644
--- a/runtime/vm/isolate.cc
+++ b/runtime/vm/isolate.cc
@@ -2557,9 +2557,12 @@ Thread* Isolate::ScheduleThread(bool is_mutator, bool bypass_safepoint) {
     os_thread->set_thread(thread);
     if (is_mutator) {
       mutator_thread_ = thread;

[rmacnak, 2017/07/25 21:02:45]

Consider lazy allocation of the TLAB.

[danunez, 2017/07/26 20:19:20]

Done.

-      if (this != Dart::vm_isolate()) {
-        mutator_thread_->set_top(heap()->new_space()->top());
-        mutator_thread_->set_end(heap()->new_space()->end());
+      if (Dart::vm_isolate() != NULL && heap() != Dart::vm_isolate()->heap()) {
+        intptr_t tlab_size = heap()->CalculateTLABSize();
+        uword top = heap()->new_space()->TryAllocateNewTLAB(tlab_size);
+        ASSERT(top != 0);
+        mutator_thread_->set_top(top);
+        mutator_thread_->set_end(heap()->new_space()->top());
       }
     }
     Thread::SetCurrent(thread);
@@ -2600,11 +2603,11 @@ void Isolate::UnscheduleThread(Thread* thread,
   OSThread::SetCurrent(os_thread);
   if (is_mutator) {
     if (this != Dart::vm_isolate()) {
-      heap()->new_space()->set_top(mutator_thread_->top_);
-      heap()->new_space()->set_end(mutator_thread_->end_);
+      // Ensure the new space is pointing right after the last object allocated.
+      heap()->new_space()->set_top(mutator_thread_->top());
     }
-    mutator_thread_->top_ = 0;
-    mutator_thread_->end_ = 0;
+    mutator_thread_->set_top(0);
+    mutator_thread_->set_end(0);
     mutator_thread_ = NULL;
   }
   thread->isolate_ = NULL;