LwIP\src\include\lwip\中第1913行如下：

/** LWIP_NETCONN_FULLDUPLEX==1: Enable code that allows reading from one thread,

• writing from a 2nd thread and closing from a 3rd thread at the same time.
• ATTENTION: This is currently really alpha! Some requirements:
• • LWIP_NETCONN_SEM_PER_THREAD==1 is required to use one socket/netconn from
• multiple threads at once *
• • sys_mbox_free() has to unblock receive tasks waiting on recvmbox/acceptmbox
• and prevent a task pending on this during/after deletion
  */

#if !defined LWIP_NETCONN_FULLDUPLEX || defined DOXYGEN
#define LWIP_NETCONN_FULLDUPLEX 1
#endif