process.channel
如果Node.js进程是由IPC channel(请看 Child Process 文档) 方式创建的， process.channel属性保存IPC channel的引用。
如果IPC channel不存在，此属性值为undefined。
If the Node.js process was spawned with an IPC channel (see the
Child Process documentation), the process.channel
property is a reference to the IPC channel. If no IPC channel exists, this
property is undefined.