Changes new space allocation from simple bump pointer allocation from

runtime/vm/scavenger.cc

Index: runtime/vm/scavenger.cc
diff --git a/runtime/vm/scavenger.cc b/runtime/vm/scavenger.cc
index 32d62e000906025ed067aaa6032adfd2f326b1a0..0b34a57709d9b0e5ce2f510695d931e8bff6c19b 100644
--- a/runtime/vm/scavenger.cc
+++ b/runtime/vm/scavenger.cc
@@ -394,13 +394,6 @@ SemiSpace* Scavenger::Prologue(Isolate* isolate, bool invoke_api_callbacks) {
   resolved_top_ = top_;
   end_ = to_->end();
 
-  // Throw out the old information about the from space
-  if (isolate->IsMutatorThreadScheduled()) {
-    Thread* mutator_thread = isolate->mutator_thread();
-    mutator_thread->set_top(top_);
-    mutator_thread->set_end(end_);
-  }
-
   return from;
 }
 
@@ -410,12 +403,12 @@ void Scavenger::Epilogue(Isolate* isolate,
   // All objects in the to space have been copied from the from space at this
   // moment.
 
-  // Ensure the mutator thread now has the up-to-date top_ and end_ of the
-  // semispace
+  // Ensure the mutator thread will fail the next allocation. This will force
+  // mutator to allocate a new TLAB
   if (isolate->IsMutatorThreadScheduled()) {
     Thread* thread = isolate->mutator_thread();
-    thread->set_top(top_);
-    thread->set_end(end_);
+    thread->set_top(0);
+    thread->set_end(0);
   }
 
   double avg_frac = stats_history_.Get(0).PromoCandidatesSuccessFraction();
@@ -722,31 +715,49 @@ void Scavenger::ProcessWeakReferences() {
   }
 }
 
-void Scavenger::FlushTLS() const {
+uword Scavenger::FlushTLS() const {
   ASSERT(heap_ != NULL);
-  if (heap_->isolate()->IsMutatorThreadScheduled()) {
+  uword saved_top = top_;
+  if (heap_->isolate()->IsMutatorThreadScheduled() && !scavenging_) {
     Thread* mutator_thread = heap_->isolate()->mutator_thread();
-    mutator_thread->heap()->new_space()->set_top(mutator_thread->top());
+    saved_top = mutator_thread->heap()->new_space()->top();
+    if (mutator_thread->HasActiveTLAB()) {
+      ASSERT(mutator_thread->top() <=
+             mutator_thread->heap()->new_space()->top());
+      mutator_thread->heap()->new_space()->set_top(mutator_thread->top());
+    }
+  }
+  return saved_top;
+}
+
+void Scavenger::UnflushTLS(uword value) const {
+  ASSERT(heap_ != NULL);
+  if (heap_->isolate()->IsMutatorThreadScheduled() && !scavenging_) {
+    Thread* mutator_thread = heap_->isolate()->mutator_thread();
+    mutator_thread->heap()->new_space()->set_top(value);
+    ASSERT(mutator_thread->top() <= mutator_thread->heap()->new_space()->top());
   }
 }
 
 void Scavenger::VisitObjectPointers(ObjectPointerVisitor* visitor) const {
-  FlushTLS();
+  uword saved_top = FlushTLS();
   uword cur = FirstObjectStart();
   while (cur < top_) {
     RawObject* raw_obj = RawObject::FromAddr(cur);
     cur += raw_obj->VisitPointers(visitor);
   }
+  UnflushTLS(saved_top);
 }
 
 void Scavenger::VisitObjects(ObjectVisitor* visitor) const {
-  FlushTLS();
+  uword saved_top = FlushTLS();
   uword cur = FirstObjectStart();
   while (cur < top_) {
     RawObject* raw_obj = RawObject::FromAddr(cur);
     visitor->VisitObject(raw_obj);
     cur += raw_obj->Size();
   }
+  UnflushTLS(saved_top);
 }
 
 void Scavenger::AddRegionsToObjectSet(ObjectSet* set) const {
@@ -755,19 +766,21 @@ void Scavenger::AddRegionsToObjectSet(ObjectSet* set) const {
 
 RawObject* Scavenger::FindObject(FindObjectVisitor* visitor) const {
   ASSERT(!scavenging_);
-  FlushTLS();
+  uword saved_top = FlushTLS();
   uword cur = FirstObjectStart();
   if (visitor->VisitRange(cur, top_)) {
     while (cur < top_) {
       RawObject* raw_obj = RawObject::FromAddr(cur);
       uword next = cur + raw_obj->Size();
       if (visitor->VisitRange(cur, next) && raw_obj->FindObject(visitor)) {
+        UnflushTLS(saved_top);
         return raw_obj;  // Found object, return it.
       }
       cur = next;
     }
     ASSERT(cur == top_);
   }
+  UnflushTLS(saved_top);
   return Object::null();
 }
 
@@ -802,6 +815,10 @@ void Scavenger::Scavenge(bool invoke_api_callbacks) {
   int64_t post_safe_point = OS::GetCurrentMonotonicMicros();
   heap_->RecordTime(kSafePoint, post_safe_point - pre_safe_point);
 
+  if (thread->IsMutatorThread() && isolate->IsMutatorThreadScheduled()) {

[rmacnak, 2017/07/26 21:30:30]

Re: thread->IsMutatorThread()

What if the GC was started by a background thread, in which case
Thread::Current() != isolate->mutator_thread()? The mutator thread's tlab would
still need to be cleared.

[danunez, 2017/07/26 22:07:12]

Right. Now modified to grab the mutator thread and abandon its TLAB.

+    heap_->AbandonRemainingTLAB(thread);
+  }
+
   // TODO(koda): Make verification more compatible with concurrent sweep.
   if (FLAG_verify_before_gc && !FLAG_concurrent_sweep) {
     OS::PrintErr("Verifying before Scavenge...");
@@ -915,7 +932,9 @@ void Scavenger::Evacuate() {
 
   if (heap_->isolate()->IsMutatorThreadScheduled()) {
     Thread* mutator_thread = heap_->isolate()->mutator_thread();
-    survivor_end_ = mutator_thread->top();
+    if (mutator_thread->HasActiveTLAB()) {
+      survivor_end_ = mutator_thread->top();
+    }
   }
 
   Scavenge();