Revert r1900, r1897 and r1895 which are all gc changes. The changes

to the page iterator leads to occasional crashes in tests.
Review URL: http://codereview.chromium.org/113262

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1915 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/heap.cc

@@ -538,7 +538,7 @@ class ScavengeVisitor: public ObjectVisitor {
 
 
 // Shared state read by the scavenge collector and set by ScavengeObject.
-static Address promoted_rear = NULL;
+static Address promoted_top = NULL;
 
 
 #ifdef DEBUG
@@ -554,34 +554,24 @@ class VerifyNonPointerSpacePointersVisitor: public ObjectVisitor {
     }
   }
 };
-
-
-static void VerifyNonPointerSpacePointers() {
-  // Verify that there are no pointers to new space in spaces where we
-  // do not expect them.
-  VerifyNonPointerSpacePointersVisitor v;
-  HeapObjectIterator code_it(Heap::code_space());
-  while (code_it.has_next()) {
-    HeapObject* object = code_it.next();
-    if (object->IsCode()) {
-      Code::cast(object)->ConvertICTargetsFromAddressToObject();
-      object->Iterate(&v);
-      Code::cast(object)->ConvertICTargetsFromObjectToAddress();
-    } else {
-      // If we find non-code objects in code space (e.g., free list
-      // nodes) we want to verify them as well.
-      object->Iterate(&v);
-    }
-  }
-
-  HeapObjectIterator data_it(Heap::old_data_space());
-  while (data_it.has_next()) data_it.next()->Iterate(&v);
-}
 #endif
 
 void Heap::Scavenge() {
 #ifdef DEBUG
-  if (FLAG_enable_slow_asserts) VerifyNonPointerSpacePointers();
+  if (FLAG_enable_slow_asserts) {
+    VerifyNonPointerSpacePointersVisitor v;
+    HeapObjectIterator it(code_space_);
+    while (it.has_next()) {
+      HeapObject* object = it.next();
+      if (object->IsCode()) {
+        Code::cast(object)->ConvertICTargetsFromAddressToObject();
+      }
+      object->Iterate(&v);
+      if (object->IsCode()) {
+        Code::cast(object)->ConvertICTargetsFromObjectToAddress();
+      }
+    }
+  }
 #endif
 
   gc_state_ = SCAVENGE;
@@ -606,70 +596,72 @@ void Heap::Scavenge() {
   new_space_.Flip();
   new_space_.ResetAllocationInfo();
 
-  // We need to sweep newly copied objects which can be either in the
-  // to space or promoted to the old generation.  For to-space
-  // objects, we treat the bottom of the to space as a queue.  Newly
-  // copied and unswept objects lie between a 'front' mark and the
-  // allocation pointer.
+  // We need to sweep newly copied objects which can be in either the to space
+  // or the old space.  For to space objects, we use a mark.  Newly copied
+  // objects lie between the mark and the allocation top.  For objects
+  // promoted to old space, we write their addresses downward from the top of
+  // the new space.  Sweeping newly promoted objects requires an allocation
+  // pointer and a mark.  Note that the allocation pointer 'top' actually
+  // moves downward from the high address in the to space.
   //
-  // Promoted objects can go into various old-generation spaces, and
-  // can be allocated internally in the spaces (from the free list).
-  // We treat the top of the to space as a queue of addresses of
-  // promoted objects.  The addresses of newly promoted and unswept
-  // objects lie between a 'front' mark and a 'rear' mark that is
-  // updated as a side effect of promoting an object.
-  //
-  // There is guaranteed to be enough room at the top of the to space
-  // for the addresses of promoted objects: every object promoted
-  // frees up its size in bytes from the top of the new space, and
-  // objects are at least one pointer in size.
-  Address new_space_front = new_space_.ToSpaceLow();
-  Address promoted_front = new_space_.ToSpaceHigh();
-  promoted_rear = new_space_.ToSpaceHigh();
+  // There is guaranteed to be enough room at the top of the to space for the
+  // addresses of promoted objects: every object promoted frees up its size in
+  // bytes from the top of the new space, and objects are at least one pointer
+  // in size.  Using the new space to record promoted addresses makes the
+  // scavenge collector agnostic to the allocation strategy (eg, linear or
+  // free-list) used in old space.
+  Address new_mark = new_space_.ToSpaceLow();
+  Address promoted_mark = new_space_.ToSpaceHigh();
+  promoted_top = new_space_.ToSpaceHigh();
 
   ScavengeVisitor scavenge_visitor;
   // Copy roots.
   IterateRoots(&scavenge_visitor);
 
-  // Copy objects reachable from weak pointers.
-  GlobalHandles::IterateWeakRoots(&scavenge_visitor);
-
-  // Copy objects reachable from the old generation.  By definition,
-  // there are no intergenerational pointers in code or data spaces.
+  // Copy objects reachable from the old generation.  By definition, there
+  // are no intergenerational pointers in code or data spaces.
   IterateRSet(old_pointer_space_, &ScavengePointer);
   IterateRSet(map_space_, &ScavengePointer);
   lo_space_->IterateRSet(&ScavengePointer);
 
-  do {
-    ASSERT(new_space_front <= new_space_.top());
-    ASSERT(promoted_front >= promoted_rear);
-
-    // The addresses new_space_front and new_space_.top() define a
-    // queue of unprocessed copied objects.  Process them until the
-    // queue is empty.
-    while (new_space_front < new_space_.top()) {
-      HeapObject* object = HeapObject::FromAddress(new_space_front);
-      object->Iterate(&scavenge_visitor);
-      new_space_front += object->Size();
-    }
+  bool has_processed_weak_pointers = false;
+
+  while (true) {
+    ASSERT(new_mark <= new_space_.top());
+    ASSERT(promoted_mark >= promoted_top);
 
-    // The addresses promoted_front and promoted_rear define a queue
-    // of unprocessed addresses of promoted objects.  Process them
-    // until the queue is empty.
-    while (promoted_front > promoted_rear) {
-      promoted_front -= kPointerSize;
-      HeapObject* object =
-          HeapObject::cast(Memory::Object_at(promoted_front));
-      object->Iterate(&scavenge_visitor);
-      UpdateRSet(object);
+    // Copy objects reachable from newly copied objects.
+    while (new_mark < new_space_.top() || promoted_mark > promoted_top) {
+      // Sweep newly copied objects in the to space.  The allocation pointer
+      // can change during sweeping.
+      Address previous_top = new_space_.top();
+      SemiSpaceIterator new_it(new_space(), new_mark);
+      while (new_it.has_next()) {
+        new_it.next()->Iterate(&scavenge_visitor);
+      }
+      new_mark = previous_top;
+
+      // Sweep newly copied objects in the old space.  The promotion 'top'
+      // pointer could change during sweeping.
+      previous_top = promoted_top;
+      for (Address current = promoted_mark - kPointerSize;
+           current >= previous_top;
+           current -= kPointerSize) {
+        HeapObject* object = HeapObject::cast(Memory::Object_at(current));
+        object->Iterate(&scavenge_visitor);
+        UpdateRSet(object);
+      }
+      promoted_mark = previous_top;
     }
 
-    // Take another spin if there are now unswept objects in new space
-    // (there are currently no more unswept promoted objects).
-  } while (new_space_front < new_space_.top());
+    if (has_processed_weak_pointers) break;  // We are done.
+    // Copy objects reachable from weak pointers.
+    GlobalHandles::IterateWeakRoots(&scavenge_visitor);
+    has_processed_weak_pointers = true;
+  }
 
   // Set age mark.
-  new_space_.set_age_mark(new_space_.top());
+  new_space_.set_age_mark(new_mark);
 
   LOG(ResourceEvent("scavenge", "end"));
 
@@ -890,8 +882,8 @@ void Heap::ScavengeObjectSlow(HeapObject** p, HeapObject* object) {
       if (target_space == Heap::old_pointer_space_) {
         // Record the object's address at the top of the to space, to allow
         // it to be swept by the scavenger.
-        promoted_rear -= kPointerSize;
-        Memory::Object_at(promoted_rear) = *p;
+        promoted_top -= kPointerSize;
+        Memory::Object_at(promoted_top) = *p;
       } else {
 #ifdef DEBUG
         // Objects promoted to the data space should not have pointers to

src/spaces-inl.h

@@ -64,16 +64,15 @@ HeapObject* HeapObjectIterator::next() {
 // PageIterator
 
 bool PageIterator::has_next() {
-  return prev_page_ != stop_page_;
+  return cur_page_ != stop_page_;
 }
 
 
 Page* PageIterator::next() {
   ASSERT(has_next());
-  prev_page_ = (prev_page_ == NULL)
-               ? space_->first_page_
-               : prev_page_->next_page();
-  return prev_page_;
+  Page* result = cur_page_;
+  cur_page_ = cur_page_->next_page();
+  return result;
 }
 
 

src/spaces.cc

@@ -111,17 +111,17 @@ void HeapObjectIterator::Verify() {
 // -----------------------------------------------------------------------------
 // PageIterator
 
-PageIterator::PageIterator(PagedSpace* space, Mode mode) : space_(space) {
-  prev_page_ = NULL;
+PageIterator::PageIterator(PagedSpace* space, Mode mode) {
+  cur_page_ = space->first_page_;
   switch (mode) {
     case PAGES_IN_USE:
-      stop_page_ = space->AllocationTopPage();
+      stop_page_ = space->AllocationTopPage()->next_page();
       break;
     case PAGES_USED_BY_MC:
-      stop_page_ = space->MCRelocationTopPage();
+      stop_page_ = space->MCRelocationTopPage()->next_page();
       break;
     case ALL_PAGES:
-      stop_page_ = space->last_page_;
+      stop_page_ = Page::FromAddress(NULL);
       break;
     default:
       UNREACHABLE();
@@ -496,11 +496,8 @@ bool PagedSpace::Setup(Address start, size_t size) {
   accounting_stats_.ExpandSpace(num_pages * Page::kObjectAreaSize);
   ASSERT(Capacity() <= max_capacity_);
 
-  // Sequentially initialize remembered sets in the newly allocated
-  // pages and cache the current last page in the space.
   for (Page* p = first_page_; p->is_valid(); p = p->next_page()) {
     p->ClearRSet();
-    last_page_ = p;
   }
 
   // Use first_page_ for allocation.
@@ -679,11 +676,9 @@ bool PagedSpace::Expand(Page* last_page) {
 
   MemoryAllocator::SetNextPage(last_page, p);
 
-  // Sequentially clear remembered set of new pages and and cache the
-  // new last page in the space.
+  // Clear remembered set of new pages.
   while (p->is_valid()) {
     p->ClearRSet();
-    last_page_ = p;
     p = p->next_page();
   }
 
@@ -728,12 +723,10 @@ void PagedSpace::Shrink() {
   Page* p = MemoryAllocator::FreePages(last_page_to_keep->next_page());
   MemoryAllocator::SetNextPage(last_page_to_keep, p);
 
-  // Since pages are only freed in whole chunks, we may have kept more
-  // than pages_to_keep.  Count the extra pages and cache the new last
-  // page in the space.
+  // Since pages are only freed in whole chunks, we may have kept more than
+  // pages_to_keep.
   while (p->is_valid()) {
     pages_to_keep++;
-    last_page_ = p;
     p = p->next_page();
   }
 

src/spaces.h

@@ -511,22 +511,11 @@ class ObjectIterator : public Malloced {
 //
 // A HeapObjectIterator iterates objects from a given address to the
 // top of a space. The given address must be below the current
-// allocation pointer (space top). There are some caveats.
-//
-// (1) If the space top changes upward during iteration (because of
-//     allocating new objects), the iterator does not iterate objects
-//     above the original space top. The caller must create a new
-//     iterator starting from the old top in order to visit these new
-//     objects.
-//
-// (2) If new objects are allocated below the original allocation top
-//     (e.g., free-list allocation in paged spaces), the new objects
-//     may or may not be iterated depending on their position with
-//     respect to the current point of iteration.
-//
-// (3) The space top should not change downward during iteration,
-//     otherwise the iterator will return not-necessarily-valid
-//     objects.
+// allocation pointer (space top). If the space top changes during
+// iteration (because of allocating new objects), the iterator does
+// not iterate new objects. The caller function must create a new
+// iterator starting from the old top in order to visit these new
+// objects. Heap::Scavenage() is such an example.
 
 class HeapObjectIterator: public ObjectIterator {
  public:
@@ -570,35 +559,17 @@ class HeapObjectIterator: public ObjectIterator {
 
 
 // -----------------------------------------------------------------------------
-// A PageIterator iterates the pages in a paged space.
+// A PageIterator iterates pages in a space.
 //
 // The PageIterator class provides three modes for iterating pages in a space:
-//   PAGES_IN_USE iterates pages containing allocated objects.
-//   PAGES_USED_BY_MC iterates pages that hold relocated objects during a
-//                    mark-compact collection.
+//   PAGES_IN_USE iterates pages that are in use by the allocator;
+//   PAGES_USED_BY_GC iterates pages that hold relocated objects during a
+//                    mark-compact collection;
 //   ALL_PAGES iterates all pages in the space.
-//
-// There are some caveats.
-//
-// (1) If the space expands during iteration, new pages will not be
-//     returned by the iterator in any mode.
-//
-// (2) If new objects are allocated during iteration, they will appear
-//     in pages returned by the iterator.  Allocation may cause the
-//     allocation pointer or MC allocation pointer in the last page to
-//     change between constructing the iterator and iterating the last
-//     page.
-//
-// (3) The space should not shrink during iteration, otherwise the
-//     iterator will return deallocated pages.
 
 class PageIterator BASE_EMBEDDED {
  public:
-  enum Mode {
-    PAGES_IN_USE,
-    PAGES_USED_BY_MC,
-    ALL_PAGES
-  };
+  enum Mode {PAGES_IN_USE, PAGES_USED_BY_MC, ALL_PAGES};
 
   PageIterator(PagedSpace* space, Mode mode);
 
@@ -606,9 +577,8 @@ class PageIterator BASE_EMBEDDED {
   inline Page* next();
 
  private:
-  PagedSpace* space_;
-  Page* prev_page_;  // Previous page returned.
-  Page* stop_page_;  // Page to stop at (last page returned by the iterator).
+  Page* cur_page_;  // next page to return
+  Page* stop_page_;  // page where to stop
 };
 
 
@@ -839,10 +809,6 @@ class PagedSpace : public Space {
   // The first page in this space.
   Page* first_page_;
 
-  // The last page in this space.  Initially set in Setup, updated in
-  // Expand and Shrink.
-  Page* last_page_;
-
   // Normal allocation information.
   AllocationInfo allocation_info_;