关闭父进程和子进程之间的 IPC 通道，一旦没有其他连接使其保持活动状态，则允许子进程正常退出。
Closes the IPC channel between parent and child, allowing the child to exit
gracefully once there are no other connections keeping it alive. After calling
this method the
process.connected properties in
both the parent and child (respectively) will be set to
false, and it will be
no longer possible to pass messages between the processes.
'disconnect' event will be emitted when there are no messages in the
process of being received. This will most often be triggered immediately after
When the child process is a Node.js instance (e.g. spawned using
process.disconnect() method can be invoked
within the child process to close the IPC channel as well.