// ------------------------------------------------------------------
// CompileQueue::get
//
// Get the next CompileTask from a CompileQueue

CompileTask* CompileQueue::get() {

  {- -------------------------------------------
  (1) 不要になった JIT 生成コード(nmethod)の回収作業を少しだけ行っておく. (See: [here](no1904IaU.html) for details)
      ---------------------------------------- -}

      NMethodSweeper::possibly_sweep();

  {- -------------------------------------------
  (1) キューに CopmileTask が届くまで Monitor::wait() で待機.
      ---------------------------------------- -}

      MutexLocker locker(lock());
      // Wait for an available CompileTask.
      while (_first == NULL) {
        // There is no work to be done right now.  Wait.
        if (UseCodeCacheFlushing && (!CompileBroker::should_compile_new_jobs() || CodeCache::needs_flushing())) {
          // During the emergency sweeping periods, wake up and sweep occasionally
          bool timedout = lock()->wait(!Mutex::_no_safepoint_check_flag, NmethodSweepCheckInterval*1000);
          if (timedout) {
            MutexUnlocker ul(lock());
            // When otherwise not busy, run nmethod sweeping
            NMethodSweeper::possibly_sweep();
          }
        } else {
          // During normal operation no need to wake up on timer
          lock()->wait();
        }
      }

  {- -------------------------------------------
  (1) CompilationPolicy::select_task() (を各サブクラスがオーバーライドしたもの) を呼んで, 
      キューから最適な CompileTask を取り出す.
      (取り出した CompileTask は, CompileQueue::remove() でキューからは削除しておく)
      ---------------------------------------- -}

      CompileTask* task = CompilationPolicy::policy()->select_task(this);
      remove(task);

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

      return task;
    }