结束AsyncTask和Thread的有效方案

如何结束AsyncTask

上周在项目中碰见一个问题，AsyncTask调用了cancel（true）方法后任务没有取消，造成的结果就是线程继续运行把不该返回的值返回了，源码中对cancel（）的说明如下：

/**
     * <p>Attempts to cancel execution of this task.  This attempt will
     * fail if the task has already completed, already been cancelled,
     * or could not be cancelled for some other reason. If successful,
     * and this task has not started when <tt>cancel</tt> is called,
     * this task should never run. If the task has already started,
     * then the <tt>mayInterruptIfRunning</tt> parameter determines
     * whether the thread executing this task should be interrupted in
     * an attempt to stop the task.</p>
     * 
     * <p>Calling this method will result in {@link #onCancelled(Object)} being
     * invoked on the UI thread after {@link #doInBackground(Object[])}
     * returns. Calling this method guarant