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:
- Spawning Child Processes: Node.js provides the
child_processmodule, which includes functions like
forkto create child processes.
spawnfunction launches a new process asynchronously, allowing you to execute an external command or script. It returns a
ChildProcessobject representing the spawned child process.
execfunction runs a command in a shell and buffers the output of the command. It provides the output as a callback. The
execfunction also returns a
execFilefunction is similar to
execbut allows you to execute a file directly instead of running it through a shell.
forkfunction 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.
- Inter-Process Communication (IPC): Node.js facilitates communication between the parent and child processes using streams and event-based communication.
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
'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
forkfunction is particularly useful for establishing this bidirectional message passing.
- 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
'SIGKILL', to control how the process is terminated.
- Monitoring Child Process Status: The
exitCodeproperty provides the exit code of a terminated child process. The
exitevent is emitted when a child process exits, allowing you to handle the termination event.
- Streams and Buffers: Child processes’
stderrstreams can be accessed and manipulated using methods provided by the
ChildProcessobject. These streams allow for reading and writing data to and from the child process.
- Killing a Child Process: The
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.