// returns true on success and false on error - really an error is fatal
// but this seems the normal response to library errors

static bool do_suspend(OSThread* osthread) {

  {- -------------------------------------------
  (1) os::Linux::SuspendResume::set_suspend_action() を呼んで
      処理対象の OSThread の sr フィールドに SR_SUSPEND をセットした後, 
      そのスレッドに対して pthread_kill() で SR_signum を送信する.
      ---------------------------------------- -}

      // mark as suspended and send signal
      osthread->sr.set_suspend_action(SR_SUSPEND);
      int status = pthread_kill(osthread->pthread_id(), SR_signum);

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

      assert_status(status == 0, status, "pthread_kill");

  {- -------------------------------------------
  (1) 処理対象のスレッドが sissuspend() で眠りにつくまでここで少し待機 (See: SR_handler()).  
      眠りについたのを確認したら, os::Linux::SuspendResume::set_suspend_action() を呼んで
      処理対象の OSThread の sr フィールドを SR_NONE に戻した後, リターン.
      ---------------------------------------- -}

      // check status and wait until notified of suspension
      if (status == 0) {
        for (int i = 0; !osthread->sr.is_suspended(); i++) {
          os::yield_all(i);
        }
        osthread->sr.set_suspend_action(SR_NONE);
        return true;
      }
      else {
        osthread->sr.set_suspend_action(SR_NONE);
        return false;
      }
    }