Parallel

Execute scripts in parallel.

Usage

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

parallel( files, [options,] clbk )

Executes scripts in parallel.

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: 200*1024*1024 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.

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.

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 script.

$ node <script_path>

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

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.

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 );

Notes

  • Relative file paths are resolved relative to the current working directory.
  • Ordered script output does not imply that scripts are executed in order. To preserve script order, execute the scripts sequentially via some other means.
  • Script concurrency cannot exceed the number of scripts.
  • If the script concurrency is less than the number of workers, the number of workers is reduced to match the specified concurrency.

Examples

var fs = require( 'fs' );
var path = require( 'path' );
var writeFileSync = require( '@stdlib/fs/write-file' ).sync;
var unlinkSync = require( '@stdlib/fs/unlink' ).sync;
var parallel = require( '@stdlib/utils/parallel' );

var nFiles = 100;
var files;
var opts;
var dir;

function template( id ) {
    var file = '';

    file += '\'use strict\';';

    file += 'var id;';
    file += 'var N;';
    file += 'var i;';

    file += 'id = '+id+';';
    file += 'N = 1e5;';
    file += 'console.log( \'File: %s. id: %s. N: %d.\', __filename, id, N );';

    file += 'for ( i = 0; i < N; i++ ) {';
    file += 'console.log( \'id: %s. v: %d.\', id, i );';
    file += '}';

    return file;
}

function createDir() {
    var dir = path.join( __dirname, 'examples', 'tmp' );
    fs.mkdirSync( dir );
    return dir;
}

function createScripts( dir, nFiles ) {
    var content;
    var fpath;
    var files;
    var i;

    files = new Array( nFiles );
    for ( i = 0; i < nFiles; i++ ) {
        content = template( i.toString() );
        fpath = path.join( dir, i+'.js' );
        writeFileSync( fpath, content, {
            'encoding': 'utf8'
        });
        files[ i ] = fpath;
    }
    return files;
}

function cleanup() {
    var i;

    // Delete the temporary files...
    for ( i = 0; i < files.length; i++ ) {
        unlinkSync( files[ i ] );
    }
    // Remove temporary directory:
    fs.rmdirSync( dir );
}

function done( error ) {
    if ( error ) {
        throw error;
    }
    cleanup();
    console.log( 'Done!' );
}

// Make a temporary directory to store files...
dir = createDir();

// Create temporary files...
files = createScripts( dir, nFiles );

// Set the runner options:
opts = {
    'concurrency': 3,
    'workers': 3,
    'ordered': false
};

// Run all temporary scripts:
parallel( files, opts, done );

CLI

Usage

Usage: parallel [options] <script1> <script2> ...

Options:

  -h,    --help                Print this message.
  -V,    --version             Print the package version.
         --cmd cmd             Executable file/command.
         --workers num         Number of workers.
         --concurrency num     Number of scripts to run concurrently.
         --ordered             Preserve order of script output.
         --uid uid             Process user identity.
         --gid gid             Process group identity.
         --maxbuffer size      Max buffer size for stdout and stderr.

Examples

$ parallel --cmd 'node' --workers 4 --concurrency 8 ./1.js ./2.js ./3.js ./4.js ./5.js ./6.js ./7.js ./8.js ./9.js ./10.js