// This method is called from signal handler when SIGSEGV occurs while the current
// thread tries to store to the "read-only" memory serialize page during state
// transition.

void os::block_on_serialize_page_trap() {

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

      if (TraceSafepoint) {
        tty->print_cr("Block until the serialize page permission restored");
      }

  {- -------------------------------------------
  (1) SerializePageLock のロックを取れるまで待機し, 取れたらすぐに開放して終了する.
      (これは, os::serialize_thread_states() との間で同期を取るための処理.
       See: os::serialize_thread_states())

      (なおコメントによると, 
       一般的にはシグナルハンドラの中でロックを取るのは危険だけど, 
       この場合のシグナルは同期的(SIGSEGV)だし, どこで発生するかも正確に分かっているので問題ない, 
       とのこと)
      ---------------------------------------- -}

      // When VMThread is holding the SerializePageLock during modifying the
      // access permission of the memory serialize page, the following call
      // will block until the permission of that page is restored to rw.
      // Generally, it is unsafe to manipulate locks in signal handlers, but in
      // this case, it's OK as the signal is synchronous and we know precisely when
      // it can occur.
      Thread::muxAcquire(&SerializePageLock, "set_memory_serialize_page");
      Thread::muxRelease(&SerializePageLock);
    }