1. Event Loop

• allows node.js to perform non-blocking Input/Output operations.

• How it works

  • Node.js uses a single-threaded event loop model that handles multiple concurrent operations via callbacks.
  • sync code exec --> Promises(api calls, database calls), setImmidiate(), setTimeout() with timeout

execution

1. console.log
2. Promises
3. setImmediate()
4. setTimeout()

2. Streams

• read data from a source or write data to a destination in a continuous manner.

• Readable - file read

• Writeable - file write

• Duplex - both readable and writeable

• Transform - like compression

3. Buffers

• Buffers are used to handle binary data directly in memory.

• In example:

  • hello = <Buffer 48 65 6c 6c 6f>

• Modify buffer:

  • data[0] = 0x68(h)
  • change 0th index data for data var to 'h'

4. Child processes

• Allows you to run other processes (scripts, shell commands) from Node.js using child_process module.
• we can do CPU intensive tasks, bash commands

1. exec

• import { exec } from 'child_process'
• we can execute any bash command with it
• like: ls, cd dir, mkdir folder_name, touch index.js

exec('command', (err, stdout) => {
  if(err) return console.log(err)
  console.log(`Output: ${stdout}`)
});

5. Clustering

• Clustering allows you to create child processes (workers) that all share the same server port.
• Leverage multi-core CPUs to improve performance.
• Letting you scale your app across CPU cores

if(cluster.isPrimary) {
  // if the current process is primary
  
  const numCPUs = os.cpus().length;
  // get the count of cpu cores

  console.log(`Primary PID: ${process.pid}`);
  // log the primary process id

  for(let i = 0; i < numCPUs; i++) {
    cluster.fork(); // create a worker
    // create workers equal to number of cores
  }

  cluster.on('exit', (worker, code) => {
    console.log(`Worker ${worker.process.pid} died`);
    // listens on exit process, if worker exit then logs them
  });
}
else {
  http.createServer((req, res) => {
    res.end(`Handled by worker ${process.pid}`);
    // each worker creates an http server on port 3000
    // When a request comes in, it responds with the worker’s process ID
    // Each worker runs independently but shares the port.
  }).listen(3000);

  console.log(`Worker ${process.pid} started`);
  // log every worker with process id
}

• Example output

Master PID: 11852
Worker 1148 started
Worker 9016 started
Worker 4276 started
Worker 17952 started
Worker 18292 started
Worker 2556 started
Worker 7288 started
Worker 2800 started

• If you need to kill any worker, open another terminal then run

kill 9016

• Note: If you kill Master PID, then it kills the cluster and all workers died.