# Functions
CreateListener creates a listener from inherited fd if there is no inherited fd, create a now one.
CreateUDPConn creates a udp connection from inherited fd if there is no inherited fd, create a now one.
GetAllLisenFiles returns all listen files.
GraceHandler set the signle handler for grace restart.
GraceHandler send signal USR2 to pid.
# Variables
InheritFdPrefix marks the fd inherited from parent process.