dart::GCSweeper Class Reference

#include <sweeper.h>

Public Member Functions
	GCSweeper ()
	~GCSweeper ()
bool	SweepPage (Page *page, FreeList *freelist)
intptr_t	SweepLargePage (Page *page)
intptr_t	SweepNewPage (Page *page)

Static Public Member Functions
static void	SweepConcurrent (IsolateGroup *isolate_group)

Detailed Description

Definition at line 21 of file sweeper.h.

Constructor & Destructor Documentation

GCSweeper()

dart::GCSweeper::GCSweeper ( )

inline

Definition at line 23 of file sweeper.h.

{}

~GCSweeper()

dart::GCSweeper::~GCSweeper ( )

inline

Definition at line 24 of file sweeper.h.

{}

Member Function Documentation

SweepConcurrent()

void dart::GCSweeper::SweepConcurrent ( IsolateGroup *  isolate_group )

static

Definition at line 215 of file sweeper.cc.

                                                           {
  bool result = Dart::thread_pool()->Run<ConcurrentSweeperTask>(isolate_group);
  ASSERT(result);
}

SweepLargePage()

intptr_t dart::GCSweeper::SweepLargePage

(

Page *

page

)

Definition at line 139 of file sweeper.cc.

                                             {
  ASSERT(!page->is_image());
  ASSERT(page->is_large() && !page->is_executable());
 
  intptr_t words_to_end = 0;
  ObjectPtr raw_obj = UntaggedObject::FromAddr(page->object_start());
  ASSERT(Page::Of(raw_obj) == page);
  if (raw_obj->untag()->IsMarked()) {
    raw_obj->untag()->ClearMarkBit();
    words_to_end = (raw_obj->untag()->HeapSize() >> kWordSizeLog2);
  }
#ifdef DEBUG
  // Array::MakeFixedLength creates trailing filler objects,
  // but they are always unreachable. Verify that they are not marked.
  uword current =
      UntaggedObject::ToAddr(raw_obj) + raw_obj->untag()->HeapSize();
  uword end = page->object_end();
  while (current < end) {
    ObjectPtr cur_obj = UntaggedObject::FromAddr(current);
    ASSERT(!cur_obj->untag()->IsMarked());
    intptr_t obj_size = cur_obj->untag()->HeapSize();
    memset(reinterpret_cast<void*>(current), Heap::kZapByte, obj_size);
    current += obj_size;
  }
#endif  // DEBUG
  return words_to_end;
}

SweepNewPage()

intptr_t dart::GCSweeper::SweepNewPage

(

Page *

page

)

Definition at line 18 of file sweeper.cc.

                                           {
  ASSERT(!page->is_image());
  ASSERT(!page->is_old());
  ASSERT(!page->is_executable());
 
  uword start = page->object_start();
  uword end = page->object_end();
  uword current = start;
  intptr_t free = 0;
  while (current < end) {
    ObjectPtr raw_obj = UntaggedObject::FromAddr(current);
    ASSERT(Page::Of(raw_obj) == page);
    uword tags = raw_obj->untag()->tags_.load(std::memory_order_relaxed);
    intptr_t obj_size = raw_obj->untag()->HeapSize(tags);
    if (UntaggedObject::IsMarked(tags)) {
      // Found marked object. Clear the mark bit and update swept bytes.
      raw_obj->untag()->ClearMarkBitUnsynchronized();
      ASSERT(IsAllocatableInNewSpace(obj_size));
    } else {
      uword free_end = current + obj_size;
      while (free_end < end) {
        ObjectPtr next_obj = UntaggedObject::FromAddr(free_end);
        tags = next_obj->untag()->tags_.load(std::memory_order_relaxed);
        if (UntaggedObject::IsMarked(tags)) {
          // Reached the end of the free block.
          break;
        }
        // Expand the free block by the size of this object.
        free_end += next_obj->untag()->HeapSize(tags);
      }
      obj_size = free_end - current;
#if defined(DEBUG)
      memset(reinterpret_cast<void*>(current), Heap::kZapByte, obj_size);
#endif  // DEBUG
      FreeListElement::AsElementNew(current, obj_size);
      free += obj_size;
    }
    current += obj_size;
  }
  return free;
}

SweepPage()

bool dart::GCSweeper::SweepPage	(	Page *	page,
		FreeList *	freelist
	)

Definition at line 60 of file sweeper.cc.

                                                        {
  ASSERT(!page->is_image());
  // Large executable pages are handled here. We never truncate Instructions
  // objects, so we never truncate executable pages.
  ASSERT(!page->is_large() || page->is_executable());
  DEBUG_ASSERT(freelist->mutex()->IsOwnedByCurrentThread());
 
  // Keep track whether this page is still in use.
  intptr_t used_in_bytes = 0;
 
  bool is_executable = page->is_executable();
  uword start = page->object_start();
  uword end = page->object_end();
  uword current = start;
  const bool dontneed_on_sweep = FLAG_dontneed_on_sweep;
  const uword page_size = VirtualMemory::PageSize();
 
  while (current < end) {
    ObjectPtr raw_obj = UntaggedObject::FromAddr(current);
    ASSERT(Page::Of(raw_obj) == page);
    // These acquire operations balance release operations in array
    // truncation, ensuring the writes creating the filler object are ordered
    // before the writes inserting the filler object into the freelist.
    uword tags = raw_obj->untag()->tags_.load(std::memory_order_acquire);
    intptr_t obj_size = raw_obj->untag()->HeapSize(tags);
    if (UntaggedObject::IsMarked(tags)) {
      // Found marked object. Clear the mark bit and update swept bytes.
      raw_obj->untag()->ClearMarkBit();
      used_in_bytes += obj_size;
      // Large objects should never appear on regular pages.
      ASSERT(IsAllocatableViaFreeLists(obj_size) || page->is_large());
    } else {
      uword free_end = current + obj_size;
      while (free_end < end) {
        ObjectPtr next_obj = UntaggedObject::FromAddr(free_end);
        tags = next_obj->untag()->tags_.load(std::memory_order_acquire);
        if (UntaggedObject::IsMarked(tags)) {
          // Reached the end of the free block.
          break;
        }
        // Expand the free block by the size of this object.
        free_end += next_obj->untag()->HeapSize(tags);
      }
      // Only add to the free list if not covering the whole page.
      if ((current == start) && (free_end == end)) {
        page->set_live_bytes(0);
        return false;  // Not in use.
      }
      obj_size = free_end - current;
      if (is_executable) {
        uword cursor = current;
        uword end = current + obj_size;
        while (cursor < end) {
          *reinterpret_cast<uword*>(cursor) = kBreakInstructionFiller;
          cursor += kWordSize;
        }
      } else if (UNLIKELY(dontneed_on_sweep)) {
        uword page_aligned_start = Utils::RoundUp(
            current + FreeListElement::kLargeHeaderSize, page_size);
        uword page_aligned_end = Utils::RoundDown(free_end, page_size);
        if (UNLIKELY(page_aligned_start < page_aligned_end)) {
          VirtualMemory::DontNeed(reinterpret_cast<void*>(page_aligned_start),
                                  page_aligned_end - page_aligned_start);
        }
      } else {
#if defined(DEBUG)
        memset(reinterpret_cast<void*>(current), Heap::kZapByte, obj_size);
#endif  // DEBUG
      }
      freelist->FreeLocked(current, obj_size);
    }
    current += obj_size;
  }
  ASSERT(current == end);
  ASSERT(used_in_bytes != 0);
  page->set_live_bytes(used_in_bytes);
  return true;  // In use.
}

---

The documentation for this class was generated from the following files:

• third_party/dart-lang/sdk/runtime/vm/heap/sweeper.h
• third_party/dart-lang/sdk/runtime/vm/heap/sweeper.cc