小用ACE_Acceptor

Ace_Acceptor是ACE的接收器之一，此次使用涉及了这个类的三个函数：open\accept_svc_handler\activate_svc_handler。

其中open函数的原型之一：

  /**
   * Open the contained @c PEER_ACCEPTOR object to begin listening, and
   * register with the specified reactor for accept events.  An
   * acceptor can only listen to one port at a time, so make sure to
   * @c close() the acceptor before calling @c open() again.
   *
   * The @c PEER_ACCEPTOR handle is put into non-blocking mode as a
   * safeguard against the race condition that can otherwise occur
   * between the time when the passive-mode socket handle is "ready"
   * and when the actual @c accept() call is made.  During this
   * interval, the client can shutdown the connection, in which case,
   * the @c accept() call can hang.
   *
   * @param local_addr The address to listen at.
   * @param reactor    Pointer to the ACE_Reactor instance to register
   *                   this object with. The default is the singleton.
   * @param flags      Flags to control what mode an accepted socket
   *                   will be put into after it is accepted. The only
   *                   legal value for this argument is @c ACE_NONBLOCK,
   *                   which enables non-blocking mode on the accepted
   *                   peer stream object in @c SVC_HANDLER.  The default
   *                   is 0.
   * @param use_select Affects behavior when called back by the reactor
   *                   when a connection can be accepted.  If non-zero,
   *                   this object will accept all pending connections,
   *                   instead of just the one that triggered the reactor
   *                   callback.  Uses ACE_OS::select() internally to
   *                   detect any remaining acceptable connections.
   *                   The default is 1.
   * @param reuse_addr Passed to the @c PEER_ACCEPTOR::open() method with
   *                   @p local_addr.  Generally used to request that the
   *                   OS allow reuse of the listen port.  The default is 1.
   *
   * @retval 0  Success
   * @retval -1 Failure, @c errno contains an error code.
   */
  virtual int open (const ACE_PEER_ACCEPTOR_ADDR &local_addr,
                    ACE_Reactor *reactor = ACE_Reactor::instance (),
                    int flags = 0,
                    int use_select = 1,
                    int reuse_addr = 1);

其中第一个参数，一般传入ACE_NET_Addr,在通过字符串（ip:port）构造对象后，需要检查对象是否含有效地址。即使传入无效的地址对象，open也不会报错。

第二个参数是反应器，不建议直接传入单体，这个可以传入ACE_Dev_Poll_Reactor\ACE_Select_Reactor构造出来的ACE_Reactor,在reactor激活之后，open之后才会真正的接入链接。

一旦链接接入，就会触发acceptor的handle_input调用的主要函数就是accept_svc_handler\activate_svc_handler。原生的accept_svc_handler函数中，无超时设置，在多进程接收链接，出现惊群现象时，会导致竞争不到链接的进程卡死在accept，一般情况下需要重写设置一个超时时间。原生的activate_svc_handler会直接在接收线程内触发svc的handle_input，一旦此函数有耗时操作，也会阻塞acceptor，一般会将acceptor抛入异线程再进行接收数据。