Linux pthread_exit 与返回

我有一个可连接的pthread runner函数，定义如下:

void *sumOfProducts(void *param)
{
...
pthread_exit(0);
}

这根线应该连接主线.

每当我通过Valgrind运行我的程序时，我都会得到following leaks分:

LEAK SUMMARY:
   definitely lost: 0 bytes in 0 blocks
   indirectly lost: 0 bytes in 0 blocks
     possibly lost: 0 bytes in 0 blocks
   still reachable: 968 bytes in 5 blocks
        suppressed: 0 bytes in 0 blocks

ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 15 from 10)

我查看了手册页上的pthreads，上面写着:

  The new thread terminates in one of the following ways:

   * It  calls  pthread_exit(3),  specifying  an exit status value that is
     available  to  another  thread  in  the  same  process   that   calls
     pthread_join(3).

   * It  returns  from  start_routine().   This  is  equivalent to calling
     pthread_exit(3) with the value supplied in the return statement.

   * It is canceled (see pthread_cancel(3)).

   * Any of the threads in the process calls exit(3), or the  main  thread
     performs  a  return  from main().  This causes the termination of all
     threads in the process.

神奇的是，当我用返回语句the leaks disappeared替换pthread_exit()时.

return(NULL);

我的实际问题有三个方面:

1. 有人能解释为什么返回声明没有泄露信息吗？
2. 在退出线程方面，这两个语句之间是否存在一些基本的区别？
3. 如果是这样，什么时候应该 Select 其中一个？