runtime/vm/gc_sweeper.cc

// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

#include "vm/gc_sweeper.h"

#include "vm/freelist.h"
#include "vm/globals.h"
#include "vm/heap.h"
#include "vm/pages.h"

namespace dart {

intptr_t GCSweeper::SweepPage(HeapPage* page, FreeList* freelist) {
  // Keep track of the discovered live object sizes to be able to finish
  // sweeping early. Reset the per page in_use count for the next marking phase.
  intptr_t in_use = 0;

  bool is_executable = (page->type() == HeapPage::kExecutable);
  uword start = page->object_start();
  uword end = page->object_end();
  uword current = start;

  while (current < end) {
    intptr_t obj_size;
    RawObject* raw_obj = RawObject::FromAddr(current);
    if (raw_obj->IsMarked()) {
      // Found marked object. Clear the mark bit and update swept bytes.
      raw_obj->ClearMarkBit();
      obj_size = raw_obj->Size();
      in_use += obj_size;
    } else {
      uword free_end = current + raw_obj->Size();
      while (free_end < end) {
        RawObject* next_obj = RawObject::FromAddr(free_end);
        if (next_obj->IsMarked()) {
          // Reached the end of the free block.
          break;
        }
        // Expand the free block by the size of this object.
        free_end += next_obj->Size();
      }
      obj_size = free_end - current;
      if (is_executable) {
        memset(reinterpret_cast<void*>(current), 0xcc, obj_size);
      }
      if ((current != start) || (free_end != end)) {
        // Only add to the free list if not covering the whole page.
        freelist->Free(current, obj_size);
      }
    }
    current += obj_size;
  }
  ASSERT(current == end);

  return in_use;
}


intptr_t GCSweeper::SweepLargePage(HeapPage* page) {
  RawObject* raw_obj = RawObject::FromAddr(page->object_start());
  if (!raw_obj->IsMarked()) {
    // The large object was not marked. Used size is zero, which also tells the
    // calling code that the large object page can be recycled.
    return 0;
  }
  raw_obj->ClearMarkBit();
  return raw_obj->Size();
}

}  // namespace dart