void G1CollectedHeap::collect(GCCause::Cause cause) {

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

      unsigned int gc_count_before;
      unsigned int full_gc_count_before;

  {- -------------------------------------------
  (1) total_collections() と total_full_collections() の回数を取得する.
      (なお, この処理は Heap_lock で排他して行う)
      ---------------------------------------- -}

      {
        MutexLocker ml(Heap_lock);

        // Read the GC count while holding the Heap_lock
        gc_count_before = SharedHeap::heap()->total_collections();
        full_gc_count_before = SharedHeap::heap()->total_full_collections();
      }

  {- -------------------------------------------
  (1) cause 引数の値に応じて以下のどれかを行う.

      * Concurrent Full GC を実行すべき場合
        (= cause の値に対して G1CollectedHeap::should_do_concurrent_full_gc() が true を返す場合): 

        VM_G1IncCollectionPause で initial-mark evacuation pause を実行し, 
        それによって Concurrent Mark 処理を開始させる.

      * Concurrent Full GC の必要はなく, 呼び出し元が GC_locker (= cause 引数が GCCause::_gc_locker) の場合:

        VM_G1IncCollectionPause で Minor GC を実行.

      * Concurrent Full GC の必要はなく, 呼び出し元が GC_locker 以外の場合: 

        VM_G1CollectFull で Major GC を実行.
      ---------------------------------------- -}

    {- -------------------------------------------
  (1.1) (以下が "Concurrent Full GC を実行すべき場合" の処理)
        ---------------------------------------- -}

      if (should_do_concurrent_full_gc(cause)) {
        // Schedule an initial-mark evacuation pause that will start a
        // concurrent cycle. We're setting word_size to 0 which means that
        // we are not requesting a post-GC allocation.
        VM_G1IncCollectionPause op(gc_count_before,
                                   0,     /* word_size */
                                   true,  /* should_initiate_conc_mark */
                                   g1_policy()->max_pause_time_ms(),
                                   cause);
        VMThread::execute(&op);

    {- -------------------------------------------
  (1.1) (以下が "Concurrent Full GC の必要はなく, 呼び出し元が GC_locker の場合" の処理)
        ---------------------------------------- -}

      } else {
        if (cause == GCCause::_gc_locker
            DEBUG_ONLY(|| cause == GCCause::_scavenge_alot)) {

          // Schedule a standard evacuation pause. We're setting word_size
          // to 0 which means that we are not requesting a post-GC allocation.
          VM_G1IncCollectionPause op(gc_count_before,
                                     0,     /* word_size */
                                     false, /* should_initiate_conc_mark */
                                     g1_policy()->max_pause_time_ms(),
                                     cause);
          VMThread::execute(&op);

    {- -------------------------------------------
  (1.1) (以下が "Concurrent Full GC の必要はなく, 呼び出し元が GC_locker 以外の場合" の処理)
        ---------------------------------------- -}

        } else {
          // Schedule a Full GC.
          VM_G1CollectFull op(gc_count_before, full_gc_count_before, cause);
          VMThread::execute(&op);
        }
      }
    }