C++ GenCollectedHeap::n_gens方法代码示例

void VM_GenCollectForPermanentAllocation::doit() {
  SvcGCMarker sgcm(SvcGCMarker::FULL);

  SharedHeap* heap = (SharedHeap*)Universe::heap();
  GCCauseSetter gccs(heap, _gc_cause);
  switch (heap->kind()) {
    case (CollectedHeap::GenCollectedHeap): {
      GenCollectedHeap* gch = (GenCollectedHeap*)heap;
      gch->do_full_collection(gch->must_clear_all_soft_refs(),
                              gch->n_gens() - 1);
      break;
    }
#ifndef SERIALGC
    case (CollectedHeap::G1CollectedHeap): {
      G1CollectedHeap* g1h = (G1CollectedHeap*)heap;
      g1h->do_full_collection(_gc_cause == GCCause::_last_ditch_collection);
      break;
    }
#endif // SERIALGC
    default:
      ShouldNotReachHere();
  }
  _res = heap->perm_gen()->allocate(_size, false);
  assert(heap->is_in_reserved_or_null(_res), "result not in heap");
  if (_res == NULL && GC_locker::is_active_and_needs_gc()) {
    set_gc_locked();
  }
}

/**
 * 标记清除的方式回收内存堆的垃圾对象
 * 		1.第一步: 标记所有存活的对象
 * 		2.第二步: 计算存活的对象在其内存区压缩后的偏移位置
 * 		3.第三步: 遍历所有存活的对象并修改其对应的地址映射表
 * 		4.第四步: 移动存活的对象压缩内存区
 */
void GenMarkSweep::invoke_at_safepoint(int level, ReferenceProcessor* rp,
  bool clear_all_softrefs) {
  assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");

  GenCollectedHeap* gch = GenCollectedHeap::heap();

#ifdef ASSERT
  if (gch->collector_policy()->should_clear_all_soft_refs()) {
    assert(clear_all_softrefs, "Policy should have been checked earlier");
  }
#endif

  // hook up weak ref data so it can be used during Mark-Sweep
  assert(ref_processor() == NULL, "no stomping");
  assert(rp != NULL, "should be non-NULL");
  _ref_processor = rp;
  rp->setup_policy(clear_all_softrefs);

  TraceTime t1("Full GC", PrintGC && !PrintGCDetails, true, gclog_or_tty);

  // When collecting the permanent generation methodOops may be moving,
  // so we either have to flush all bcp data or convert it into bci.
  CodeCache::gc_prologue();
  Threads::gc_prologue();

  // Increment the invocation count for the permanent generation, since it is
  // implicitly collected whenever we do a full mark sweep collection.
  gch->perm_gen()->stat_record()->invocations++;

  //本次Gc之前内存堆的使用量
  size_t gch_prev_used = gch->used();

  // Some of the card table updates below assume that the perm gen is
  // also being collected.
  assert(level == gch->n_gens() - 1, "All generations are being collected, ergo perm gen too.");

  // Capture used regions for each generation that will be
  // subject to collection, so that card table adjustments can
  // be made intelligently (see clear / invalidate further below).
  gch->save_used_regions(level, true /* perm */);

  allocate_stacks();

  mark_sweep_phase1(level, clear_all_softrefs);

  mark_sweep_phase2();

  // Don't add any more derived pointers during phase3
  COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity"));
  COMPILER2_PRESENT(DerivedPointerTable::set_active(false));

  mark_sweep_phase3(level);

  VALIDATE_MARK_SWEEP_ONLY(
    if (ValidateMarkSweep) {
      guarantee(_root_refs_stack->length() == 0, "should be empty by now");
    }
  )

jbyte CardTableRS::find_unused_youngergenP_card_value() {
  GenCollectedHeap* gch = GenCollectedHeap::heap();
  for (jbyte v = youngergenP1_card;
       v < cur_youngergen_and_prev_nonclean_card;
       v++) {
    bool seen = false;
    for (int g = 0; g < gch->n_gens()+1; g++) {
      if (_last_cur_val_in_gen[g] == v) {
	seen = true;
	break;
      }
    }
    if (!seen) return v;
  }
  ShouldNotReachHere();
  return 0;
}