TS spawn创建子进程

1.ts spawn创建进程

ts脚本 通过spawn创建一个子进程，并通过子管道进程通信。

child_process.spawn(command[, args][, options])#

History

• command <string>  需要运行可执行的目录
• args <string[]>  参数列表

• options <Object>

  • cwd <string> 子进程工作目录.
  • env <Object> 子进程环境变量  env: {             MEDIASOUP_VERSION: '3.6.14'           },
  • argv0 <string> 强制设置进程的参数0参数，如果不设置，就取comand。
  • stdio <Array> | <string> 子进程标准输出,很重要
  • detached <boolean> 子进程单独运行,父进程杀死后，他任然存在
  • uid <number> 设置进程用户标志
  • gid <number> 设置进程用户组标志
  • serialization <string> 指定用于在进程之间发送消息的序列化类型。可能的值为“json”和“advanced”。有关详细信息，请参阅高级序列化. Default: 'json'。
  • shell <boolean> | <string> If true, 在shell中运行命令。在Unix上使用“/bin/sh”，并且过程.env.ComSpec在窗户上。可以将另一个shell指定为字符串。请参见Shell要求和默认Windows Shell。默认值：false（无shell）。
  • windowsVerbatimArguments <boolean>

    在Windows上不引用或转义参数。在Unix上被忽略。当指定shell和i时，这将自动设置为true

    . Default: false.
  • windowsHide <boolean> 隐藏子进程窗口，默认为真. Default: false.
• Returns: <ChildProcess>

The child_process.spawn() 使用“command”创建子进程，创建参数列表使用“args”,如果不传，使用空列表。如果启用了shell选项，请不要将未经初始化的用户输入传递到此函数。任何包含shell元字符的输入都可以用来触发任意命令的执行。

node.js 当前用覆盖argv[0]进程.execPath启动时，所以进程.argv[0]在nod.js子进程将与从父进程传递给spawn的argv0参数不匹配，请使process.argv0而不是属性。

 

options.stdio#

History

The options.stdio option 建立了用于配置进程之间的父管道和子管道的选项. 默认情况下, 子进程 stdin, stdout, and stderr 三个管道被重定向到 subprocess.stdin, subprocess.stdout, and subprocess.stderr streams on the ChildProcess 对象中. This is equivalent to setting the options.stdio equal to ['pipe', 'pipe', 'pipe'].

For convenience, options.stdio may be one of the following strings:

• 'pipe': equivalent to ['pipe', 'pipe', 'pipe'] (the default)
• 'ignore': equivalent to ['ignore', 'ignore', 'ignore']
• 'inherit': equivalent to ['inherit', 'inherit', 'inherit'] or [0, 1, 2]

    否则，值选项.stdio是一个数组，其中每个索引对应于子级中的fd。fd 0、1和2分别对应于stdin、stdout和stderr。可以指定其他FD以在父对象和子对象之间创建其他管道。该值为以下值之一：

1. 'pipe': Create a pipe between the child process and the parent process. The parent end of the pipe is exposed to the parent as a property on the child_process object as subprocess.stdio[fd]. Pipes created for fds 0, 1, and 2 are also available as subprocess.stdin, subprocess.stdout and subprocess.stderr, respectively.

2. 'ipc': 创建用于在父级和子级之间传递消息/文件描述符的ipc通道。子进程最多可以有一个IPC stdio文件描述符。设置此选项将启用子流程.发送（）方法。如果孩子是节点.js进程中，IPC通道的存在将启用进程.发送（）和进程断开（）方法，以及子级中的“断开连接”和“消息”事件。

   Accessing the IPC channel fd in any way other than process.send() or using the IPC channel with a child process that is not a Node.js instance is not supported.

3. 'ignore': Instructs Node.js to ignore the fd in the child. While Node.js will always open fds 0, 1, and 2 for the processes it spawns, setting the fd to 'ignore' will cause Node.js to open /dev/null and attach it to the child's fd.

4. 'inherit': Pass through the corresponding stdio stream to/from the parent process. In the first three positions, this is equivalent to process.stdin, process.stdout, and process.stderr, respectively. In any other position, equivalent to 'ignore'.

5. <Stream> object: Share a readable or writable stream that refers to a tty, file, socket, or a pipe with the child process. The stream's underlying file descriptor is duplicated in the child process to the fd that corresponds to the index in the stdio array. The stream must have an underlying descriptor (file streams do not until the 'open' event has occurred).

6. Positive integer: The integer value is interpreted as a file descriptor that is currently open in the parent process. It is shared with the child process, similar to how <Stream> objects can be shared. Passing sockets is not supported on Windows.

7. null, undefined: Use default value. For stdio fds 0, 1, and 2 (in other words, stdin, stdout, and stderr) a pipe is created. For fd 3 and up, the default is 'ignore'.

const { spawn } = require('child_process');

// Child will use parent's stdios.
spawn('prg', [], { stdio: 'inherit' });

// Spawn child sharing only stderr.
spawn('prg', [], { stdio: ['pipe', 'pipe', process.stderr] });

// Open an extra fd=4, to interact with programs presenting a
// startd-style interface.
spawn('prg', [], { stdio: ['pipe', null, null, null, 'pipe'] });

It is worth noting that when an IPC channel is established between the parent and child processes, and the child is a Node.js process, the child is launched with the IPC channel unreferenced (using unref()) until the child registers an event handler for the 'disconnect' event or the 'message' event. This allows the child to exit normally without the process being held open by the open IPC channel.

On Unix-like operating systems, the child_process.spawn() method performs memory operations synchronously before decoupling the event loop from the child. Applications with a large memory footprint may find frequent child_process.spawn() calls to be a bottleneck. For more information, see V8 issue 7381.

See also: child_process.exec() and child_process.fork().

2.mediasoup创建进程

    mediasoup通过以下命令创建work子进程，并且通过它的管道和js master通信。tsmaster 创建7个管道用于和子进程通信，前三个分部是stdin,stdout,stderr,后两个是通道和负载。

如下是传递参数的个数： 

https://nodejs.org/api/child_process.html#child_process_child_process_spawn_command_args_options