How does Node.js handle child processes

Node.js handles child processes by providing a set of APIs and mechanisms to create, control, and communicate with child processes. These mechanisms allow Node.js to spawn and manage separate operating system processes and enable communication between the parent and child processes. Here’s an overview of how Node.js handles child processes:

1. Spawning Child Processes: Node.js provides the child_process module, which includes functions like spawn, exec, execFile, and fork to create child processes.
   • The spawn function launches a new process asynchronously, allowing you to execute an external command or script. It returns a ChildProcess object representing the spawned child process.
   • The exec function runs a command in a shell and buffers the output of the command. It provides the output as a callback. The exec function also returns a ChildProcess object.
   • The execFile function is similar to exec but allows you to execute a file directly instead of running it through a shell.
   • The fork function is specifically designed for creating child processes that communicate with each other through inter-process communication (IPC). It spawns a new Node.js process and establishes a communication channel between the parent and child processes.
2. Inter-Process Communication (IPC): Node.js facilitates communication between the parent and child processes using streams and event-based communication.
   • stdin, stdout, and stderr: Child processes have their own standard input (stdin), output (stdout), and error (stderr) streams. These streams can be accessed and manipulated to send input to the child process and receive its output or error messages.
   • Events and Event Listeners: Child processes emit various events, such as 'exit', 'close', 'message', etc. You can listen to these events using event listeners to perform actions when specific events occur in the child process.
   • Message Passing: Child processes in Node.js can communicate with the parent process using message passing. They can send messages to the parent process and vice versa through the IPC channel. The fork function is particularly useful for establishing this bidirectional message passing.
3. Controlling and Managing Child Processes: Node.js provides several methods and properties to control and manage child processes.
   • Killing a Child Process: The kill() method allows you to terminate a child process programmatically. You can also send a specific signal, such as 'SIGTERM' or 'SIGKILL', to control how the process is terminated.
   • Monitoring Child Process Status: The exitCode property provides the exit code of a terminated child process. The exit event is emitted when a child process exits, allowing you to handle the termination event.
   • Streams and Buffers: Child processes’ stdin, stdout, and stderr streams can be accessed and manipulated using methods provided by the ChildProcess object. These streams allow for reading and writing data to and from the child process.

Node.js leverages these mechanisms to effectively handle child processes, enabling developers to execute external commands or scripts, offload CPU-intensive tasks to separate processes, parallelize workloads, and facilitate inter-process communication within a Node.js application.