int os::sleep(Thread* thread, jlong millis, bool interruptible) {

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

      assert(thread == Thread::current(),  "thread consistency check");

  {- -------------------------------------------
  (1) #TODO
      ---------------------------------------- -}

      // TODO-FIXME: this should be removed.
      // On Solaris machines (especially 2.5.1) we found that sometimes the VM gets into a live lock
      // situation with a JavaThread being starved out of a lwp. The kernel doesn't seem to generate
      // a SIGWAITING signal which would enable the threads library to create a new lwp for the starving
      // thread. We suspect that because the Watcher thread keeps waking up at periodic intervals the kernel
      // is fooled into believing that the system is making progress. In the code below we block the
      // the watcher thread while safepoint is in progress so that it would not appear as though the
      // system is making progress.
      if (!Solaris::T2_libthread() &&
          thread->is_Watcher_thread() && SafepointSynchronize::is_synchronizing() && !Arguments::has_profile()) {
        // We now try to acquire the threads lock. Since this lock is held by the VM thread during
        // the entire safepoint, the watcher thread will  line up here during the safepoint.
        Threads_lock->lock_without_safepoint_check();
        Threads_lock->unlock();
      }

  {- -------------------------------------------
  (1) (以下の処理は, 処理対象のスレッドが JavaThread か否かに応じて, 2通りに分岐)
      ---------------------------------------- -}

  {- -------------------------------------------
  (1) (以下が, JavaThread の場合の処理)

      ThreadBlockInVM で JavaThread の状態を変更した後, 
      以下のどちらかの待機処理を行い, 
      結果をリターンする.
      * スリープ時間が 0 以下であれば, thr_yield() システムコールを呼んで yield する. (この場合, 結果は常に 0)
        (なおこちらのケースについては, 最初のバージョンの実装が 
         OSThreadWaitState を使っていなかったので, 現在でも使っていないとのこと)
      * そうでなければ, os_sleep() で眠りにつく. (この場合, 結果は os_sleep() の返値)
        (ついでに, 眠りにつく前に OSThreadWaitState で OSThread の状態変更も行っている)

      (なお, 寝ている間に java.lang.Thread.suspend() で suspend 状態にされているかもしれないので, 
       目が覚めた後に JavaThread::check_and_wait_while_suspended() でチェックを行っている.
       もし suspend されていれば, すぐにはリターンせず, resume されるまでこの中で待機する
       (See: java.lang.Thread.suspend()))


      #TODO  JavaThread::set_suspend_equivalent() はどういう意味がある??
      ---------------------------------------- -}

      if (thread->is_Java_thread()) {
        // This is a JavaThread so we honor the _thread_blocked protocol
        // even for sleeps of 0 milliseconds. This was originally done
        // as a workaround for bug 4338139. However, now we also do it
        // to honor the suspend-equivalent protocol.

        JavaThread *jt = (JavaThread *) thread;
        ThreadBlockInVM tbivm(jt);

        jt->set_suspend_equivalent();
        // cleared by handle_special_suspend_equivalent_condition() or
        // java_suspend_self() via check_and_wait_while_suspended()

        int ret_code;
        if (millis <= 0) {
          thr_yield();
          ret_code = 0;
        } else {
          // The original sleep() implementation did not create an
          // OSThreadWaitState helper for sleeps of 0 milliseconds.
          // I'm preserving that decision for now.
          OSThreadWaitState osts(jt->osthread(), false /* not Object.wait() */);

          ret_code = os_sleep(millis, interruptible);
        }

        // were we externally suspended while we were waiting?
        jt->check_and_wait_while_suspended();

        return ret_code;
      }

  {- -------------------------------------------
  (1) (以下が, JavaThread 以外の場合の処理)

      以下のどちらかの処理を行う.
      * スリープ時間が 0 以下であれば, thr_yield() システムコールを呼んで yield した後, リターン.
      * そうでなければ, os_sleep() で眠りについた後, リターン.
        (ついでに, 眠りにつく前に OSThreadWaitState で OSThread の状態変更も行っている)
      ---------------------------------------- -}

      // non-JavaThread from this point on:

      if (millis <= 0) {
        thr_yield();
        return 0;
      }

      OSThreadWaitState osts(thread->osthread(), false /* not Object.wait() */);

      return os_sleep(millis, interruptible);
    }