Usage

`javascript
var parallel = require( '@stdlib/utils-parallel' );
`

#### parallel( files, \[options,] clbk )

Executes scripts in parallel.

`text
var files = [
'./a.js',
'./b.js'
];

function done( error ) {
if ( error ) {
console.error( 'Exit code: '+error.code );
console.error( 'Signal: '+error.signal );
throw error;
}
console.log( 'Done!' );
}

parallel( files, done );
`

The function accepts the following options:

- cmd: executable file/command. Default: 'node'.
- workers: number of workers. Default: number of CPUs minus 1.
- concurrency: number of scripts to execute concurrently. Default: options.workers.
- ordered: boolean indicating whether to preserve the order of script output. Default: false.
- maxBuffer: maximum child process stdio buffer size. This option is only applied when options.ordered = true. Default: 20010241024 bytes.
- uid: child process user identity.
- gid: child process group identity.

By default, the number of workers running scripts is equal to the number of CPUs minus 1 (master process). To adjust the number of workers, set the workers option.

`text
var files = [
'./a.js',
'./b.js'
];

function done( error ) {
if ( error ) {
console.error( 'Exit code: '+error.code );
console.error( 'Signal: '+error.signal );
throw error;
}
console.log( 'Done!' );
}

var opts = {
'workers': 8
};

parallel( files, opts, done );
`

By default, the number of scripts running concurrently is equal to the number of workers. To adjust the concurrency, set the concurrency option.

`text
var files = [
'./a.js',
'./b.js'
];

function done( error ) {
if ( error ) {
console.error( 'Exit code: '+error.code );
console.error( 'Signal: '+error.signal );
throw error;
}
console.log( 'Done!' );
}

var opts = {
'concurrency': 6
};

parallel( files, opts, done );
`

By specifying a concurrency greater than the number of workers, a worker may be executing more than 1 script at any one time. While not likely to be advantageous for synchronous scripts, setting a higher concurrency may be advantageous for scripts performing asynchronous tasks.

By default, each script is executed as a [Node.js][node-js] script.

`text
$ node
`

To run scripts via an alternative executable or none at all, set the cmd option.

`text
var files = [
'./a.js',
'./b.js'
];

function done( error ) {
if ( error ) {
console.error( 'Exit code: '+error.code );
console.error( 'Signal: '+error.signal );
throw error;
}
console.log( 'Done!' );
}

var opts = {
'cmd': '' // e.g., if scripts contain a shebang
};

parallel( files, opts, done );
`

By default, the stdio output for each script is interleaved; i.e., the stdio output from one script may be interleaved with the stdio output from one or more other scripts. To preserve the stdio output order for each script, set the ordered option to true.

`text
var files = [
'./a.js',
'./b.js'
];

function done( error ) {
if ( error ) {
console.error( 'Exit code: '+error.code );
console.error( 'Signal: '+error.signal );
throw error;
}
console.log( 'Done!' );
}

var opts = {
'ordered': true
};

parallel( files, opts, done );
`