+ /** Stop a thread gracefully.
+ * First, this function asks the thread to terminate by calling Thread::SetExitFlag().
+ * Next, it waits until the thread terminates (on the operating system level). Finally,
+ * all OS-level resources associated with the thread are released. The Thread instance
+ * passed to the function is NOT freed.
+ * When this function returns, the thread is stopped and you can destroy it or restart it
+ * at a later point.
+ * Stopping a thread that is not running is a bug.
+ * @param thread The thread to stop.