java - 当 Java 线程结束时，可运行类是否超出范围？

Question

如果我创建一个实现 Runnable 的对象，并用它启动一个线程...

ArrayList<Thread> threadlist = new ArrayList<Thread>();
{
  MergeThread mmt = new MergeThread();
  Thread t = new Thread(mmt);
  threadlist.add(mmt);
  t.start();
}

t.join();
Thread t = threadlist.get(0);

此时 mmt 保证存在，或者如果垃圾收集得到它，它可能已经消失。

我想问的是，线程结束后，Thread 对象是否继续保留 Runnable 类。

编辑:上面应该说的有误threadlist.add(t);

Answer 1

来自source of the Thread class :

/**
 * This method is called by the system to give a Thread
 * a chance to clean up before it actually exits.
 */
private void exit() {
if (group != null) {
    group.remove(this);
    group = null;
}
/* Aggressively null out all reference fields: see bug 4006245 */
target = null;
/* Speed the release of some of these resources */
    threadLocals = null;
    inheritableThreadLocals = null;
    inheritedAccessControlContext = null;
    blocker = null;
    uncaughtExceptionHandler = null;
}

因此系统调用Thread#exit() 并释放对target(线程正在运行的runnable)的引用。

还有一个bug report #4006245 on bugs.sun.com这是指清除 target 引用。