Node.js – Extensions

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Node.js – Extensions

1. Node.js – Extensions

Node.js runs in single-thread mode, but it uses an event-driven programming model for concurrency, enabling the creation of child processes that promote parallelism across multiple threads. system based on multi-core CPU.

The child process has 3 streams, child.stdin, child.stdout and child.stderr, which can be shared with the parent process’s stdio stream.

Node provides the following child_process module to create child processes:

– exec: the child_process.exec method runs a command in the shell/console and returns the output buffer.

– spawn: child_process.spawn method launches a new process with the given command.

– forks: the child_process.fork method is a special case of spawn() to create child processes.

2. Exec() method in Node.js

The child_process.exec method runs a command in the shell and outputs buffer. It uses the signature below:

child_process.exec(command[, options]callback)

In there:

– command (string) is the command to run, with space-separated parameters.

– options (object) may include one or more of the following options:

+ cwd (string): child process’s current working directory.

+ env (object): key – value pair Environment.

+ encoding (string) (default: ‘utf8’).

+ shell (string): Shell to execute commands, where ‘/bin/sh’ defaults on UNIX, ‘cmd.exe’ on Windows. The shell will understand the switch command -c on UNIX or /s/c on Windows. On Windows, command line parsing must be compatible with cmd.exe.

+ timeout (number) (default: 0).

+ maxBuffer (Number) (default: 200 * 1024).

+ killSignal(string) (default: ‘SIGTERM’).

+ uid (number): set the user identity of the process.

+ gid (number): set the group identity of the process.

– Callbacks: This function takes three arguments, error, stdout, and stderr, which are called with output when the process terminates.

The exec() method returns a buffer with the maximum size and waits for the process to terminate, trying to return all buffer data at once.

For example

Create 2 js files named respectively support.js and master.js:

File: support.js:

console.log(“Child Process ” + process.argv[2] + “executed.” );

File: master.js:

const fs = require(‘fs’);

const child_process = require(‘child_process’);

for(var i=0; i

var workerProcess = child_process.exec(‘node support.js ‘+i,function

(error, stdout, stderr) {

if (error) {

console.log(error.stack);

console.log(‘Error code: ‘+error.code);

console.log(‘Signal received: ‘+error.signal);

}

console.log(‘stdout: ‘ + stdout);

console.log(‘stderr: ‘ + stderr);

});

workerProcess.on(‘exit’, function (code) {

console.log(‘Child process exited with exit code ‘+code);

});

}

Next run the master.js file to see the results:

node master.js

Confirm output, server has started.

Child process exited with exit code 0

stdout: Child Process 1 executed.

stderr:

Child process exited with exit code 0

stdout: Child Process 0 executed.

stderr:

Child process exited with exit code 0

stdout: Child Process 2 executed.

3. The spawn() method in Node.js

The child_process.spawn method launches a new process with the given command, which uses the following signature:

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

In there:

– Command (string) is the command to run.

– args (array): argument string list.

– options (object) may include one or more of the following options:

+ cwd (string): child process’s current working directory.

+ env (object): key – value pair Environment.

+ stdio (array) Child’s stdio configuration string.

+ customFds (array): files are not acceptable for child use for stdio.

+ detached (Boolean): child will be at the top of the process.

+ uid (number): set the user identity of the process.

+ gid (number): set the group identity of the process.

The spawn() method returns streams (stdout &stderr) and is used when the process describes the block of data. spawn() starts receiving a response as soon as the process starts executing.

For example

Create 2 js files named respectively support.js and master.js:

File: support.js:

console.log(“Child Process ” + process.argv[2] + “executed.” );

File: master.js:

const child_process = require(‘child_process’);

for(var i = 0; i

var workerProcess = child_process.spawn(‘node’, [‘support.js’, i]);

workerProcess.stdout.on(‘data’, function (data) {

console.log(‘stdout: ‘ + data);

});

workerProcess.stderr.on(‘data’, function (data) {

console.log(‘stderr: ‘ + data);

});

workerProcess.on(‘close’, function (code) {

console.log(‘child process exited with code ‘ + code);

});

}

Next run master.js to see the results:

node master.js

Confirm output and start the server:

stdout: Child Process 0 executed.

child process exited with code 0

stdout: Child Process 1 executed.

stdout: Child Process 2 executed.

child process exited with code 0

child process exited with code 0

4. Node.js . fork() method

The child_process.fork method is a special case of spawn() to create Node processes, it uses the following signature:

child_process.fork(modulePath[, args][, options])

In there:

– modulePath(string): A module to run in child.

– args (array): Argument string list.

– options (object) may include one or more of the following options:

+ cwd (string): current active directory of the child process.

+ env (object): key – value pair Environment.

+ execPath (string): used to create the child process.

+ execArgv (array): list of strings of arguments assigned to the executable (default: process.execArgv).

+ silent (Boolean): if the value is true, the child’s stdin, stdout and stderr will be sent to the parent process, otherwise it will be inherited from the parent process.

+ uid (number): set the user identity of the process.

+ gid (number): set the group identity of the process.

The fork method returns an object with the communication channel built into all methods of the normal ChildProcess variant.

For example

Create 2 js files named respectively support.js and master.js:

File: support.js:

console.log(“Child Process ” + process.argv[2] + “executed.” );

File: master.js:

const fs = require(‘fs’);

const child_process = require(‘child_process’);

for(var i=0; i

var worker_process = child_process.fork(“support.js”, [i]);

worker_process.on(‘close’, function (code) {

console.log(‘child process exited with code ‘ + code);

});

}

Next run master.js to see the results:

node master.js

Confirm output and start the server:

Child Process 0 executed.

Child Process 1 executed.

Child Process 2 executed.

child process exited with code 0

child process exited with code 0

child process exited with code 0

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