// The last collection bailed out, we are running out of heap space,
// so we try to allocate the from-space, too.

HeapWord* DefNewGeneration::allocate_from_space(size_t size) {

  {- -------------------------------------------
  (1) (変数宣言など)
      ---------------------------------------- -}

      HeapWord* result = NULL;

  {- -------------------------------------------
  (1) (トレース出力)
      ---------------------------------------- -}

      if (Verbose && PrintGCDetails) {
        gclog_or_tty->print("DefNewGeneration::allocate_from_space(%u):"
                            "  will_fail: %s"
                            "  heap_lock: %s"
                            "  free: " SIZE_FORMAT,
                            size,
                            GenCollectedHeap::heap()->incremental_collection_will_fail(false /* don't consult_young */) ?
                              "true" : "false",
                            Heap_lock->is_locked() ? "locked" : "unlocked",
                            from()->free());
      }

  {- -------------------------------------------
  (1) ...#TODO であれば, ContiguousSpace::allocate() を呼んで From 領域からメモリを確保する.
      ---------------------------------------- -}

      if (should_allocate_from_space() || GC_locker::is_active_and_needs_gc()) {
        if (Heap_lock->owned_by_self() ||
            (SafepointSynchronize::is_at_safepoint() &&
             Thread::current()->is_VM_thread())) {
          // If the Heap_lock is not locked by this thread, this will be called
          // again later with the Heap_lock held.
          result = from()->allocate(size);
        } else if (PrintGC && Verbose) {
          gclog_or_tty->print_cr("  Heap_lock is not owned by self");
        }
      } else if (PrintGC && Verbose) {
        gclog_or_tty->print_cr("  should_allocate_from_space: NOT");
      }

  {- -------------------------------------------
  (1) (トレース出力)
      ---------------------------------------- -}

      if (PrintGC && Verbose) {
        gclog_or_tty->print_cr("  returns %s", result == NULL ? "NULL" : "object");
      }

  {- -------------------------------------------
  (1) 結果をリターン
      ---------------------------------------- -}

      return result;
    }