void GenCollectedHeap::collect(GCCause::Cause cause, int max_level) {

  {- -------------------------------------------
  (1) (assert)
      ---------------------------------------- -}

      // The caller doesn't have the Heap_lock
      assert(!Heap_lock->owned_by_self(), "this thread should not own the Heap_lock");

  {- -------------------------------------------
  (1) MutexLocker でロックを取った状態で, GenCollectedHeap::collect_locked() を呼び出すだけ.
      ---------------------------------------- -}

      MutexLocker ml(Heap_lock);
      collect_locked(cause, max_level);
    }