feat: add utils/async/parallel

lib/node_modules/@stdlib/utils/async/parallel/README.md

@@ -0,0 +1,297 @@
+<!--
+
+@license Apache-2.0
+
+Copyright (c) 2024 The Stdlib Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+   http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+-->
+
+# Parallel
+
+> Execute functions in parallel, passing the results of all functions to a final callback.
+
+<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->
+
+<section class="intro">
+
+</section>
+
+<!-- /.intro -->
+
+<!-- Package usage documentation. -->
+
+<section class="usage">
+
+## Usage
+
+```javascript
+var parallel = require( '@stdlib/utils/async/parallel' );
+```
+
+#### parallel( functionArray, \[options,] done )
+
+Executes functions inside `functionArray` in parallel, passing the results of all functions to a final callback.
+
+The first argument to each function is a `resolve` callback. The `resolve` callback should be invoked upon function completion. The first argument is reserved as an `error` argument (which can be `null` or void). If there is a result, it should be provided as the second argument to the `resolve` callback. Failure to invoke the `resolve` callback will prevent the `done` callback from being invoked.
+
+```javascript
+function a( resolve ) {
+    setTimeout( onTimeout, 0 );
+    function onTimeout() {
+        resolve( null, 2 );
+    }
+}
+
+function b( resolve ) {
+    setTimeout( onTimeout, 0 );
+    function onTimeout() {
+        resolve( null, 4 );
+    }
+}
+
+function done( error, out ) {
+    if ( error ) {
+        throw error;
+    }
+    console.log( out );
+    // => [ 2, 4 ]
+}
+
+var fcns = [ a, b ];
+
+parallel( fcns, done );
+```
+
+The `resolve` callback accepts two arguments: `error` and `value`. The second argument to the `resolve` callback is the output of the function. If a function function calls the `resolve` callback with a truthy error argument, the function stops executing any queued functions in case of a limit being present and calls the `done` callback for error processing.
+
+```javascript
+function a( resolve ) {
+    setTimeout( onTimeout, 0 );
+    function onTimeout() {
+        resolve( new Error( 'beep' ) );
+    }
+}
+
+function b( resolve ) {
+    setTimeout( onTimeout, 0 );
+    function onTimeout() {
+        resolve( null, 4 );
+    }
+}
+
+function done( error, out ) {
+    if ( error ) {
+        console.error( error.message );
+    }
+    // => 'beep'
+}
+
+var fcns = [ a, b ];
+
+parallel( fcns, done );
+```
+
+The function accepts the following `options`:
+
+-   **limit**: maximum number of functions to execute concurrently. Default: `infinity`.
+-   **thisArg**: execution context for each function.
+
+To limit the maximum number of functions executing in parallel, set the `limit` option.
+
+```javascript
+function a( resolve ) {
+    setTimeout( onTimeout, 0 );
+    function onTimeout() {
+        resolve( null, 2 );
+    }
+}
+
+function b( resolve ) {
+    setTimeout( onTimeout, 0 );
+    function onTimeout() {
+        resolve( null, 4 );
+    }
+}
+
+function done( error, out ) {
+    if ( error ) {
+        throw error;
+    }
+    console.log( out );
+    // => [ 2, 4 ]
+}
+
+var fcns = [ a, b ];
+
+var opts = {
+    'limit': 1
+};
+
+parallel( fcns, opts, done );
+```
+
+To set the `this` context for **all** `functions` in the provided function array, set the `thisArg` option.
+
+```javascript
+function a( resolve ) {
+    this.idx += 1;
+    resolve( null, 2 );
+}
+
+function b( resolve ) {
+    this.idx += 1;
+    resolve( null, 4 );
+}
+
+function done( error, out ) {
+    if ( error ) {
+        throw error;
+    }
+    console.log( this.idx );
+    // => 2
+}
+
+var fcns = [ a, b ];
+var ctx = {
+    'idx': 0
+};
+var opts = {
+    'thisArg': ctx
+};
+
+parallel( fcns, opts, done );
+```
+
+#### parallel.factory( functionArray, \[options,] done )
+
+Returns a reusable parallel `function`.
+
+```javascript
+function a( resolve ) {
+    setTimeout( onTimeout, 0 );
+    function onTimeout() {
+        resolve( null, 2 );
+    }
+}
+
+function b( resolve ) {
+    setTimeout( onTimeout, 0 );
+    function onTimeout() {
+        resolve( null, 4 );
+    }
+}
+
+function done( error, out ) {
+    if ( error ) {
+        throw error;
+    }
+    console.log( out );
+    // => [ 2, 4 ]
+}
+
+var fcns = [ a, b ];
+
+var run = parallel.factory( fcns, done );
+
+run();
+run();
+run();
+```
+
+</section>
+
+<!-- /.usage -->
+
+<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
+
+<section class="notes">
+
+## Notes
+
+-   The `functionArray` argument should be an array of functions to be executed in parallel.
+-   The `done` callback is invoked upon completion of all functions or upon encountering an error.
+-   The order of the results provided to the `done` callback corresponds to the order of the provided functions.
+-   The first argument applied to each function is a callback. The callback should be invoked upon function completion. The first argument is reserved as an `error` argument (which can be `null` or void). If there is a result, it should be provided as the second argument to the callback. Failure to invoke the callback will prevent the `done` callback from being invoked.
+-   This implementation does **not** guarantee that execution is asynchronous. If provided functions are synchronous, they will be executed synchronously.
+
+</section>
+
+<!-- /.notes -->
+
+<!-- Package usage examples. -->
+
+<section class="examples">
+
+## Examples
+
+<!-- eslint no-undef: "error" -->
+
+```javascript
+var parallel = require( '@stdlib/utils/async/parallel' );
+
+function foo( resolve ) {
+    setTimeout( onTimeout, 300 );
+    function onTimeout() {
+        resolve( null, 'one' );
+    }
+}
+
+function bar( resolve ) {
+    setTimeout( onTimeout, 100 );
+    function onTimeout() {
+        resolve( null, 'two' );
+    }
+}
+
+function done( error, results ) {
+    if ( error ) {
+        throw error;
+    }
+    console.log( results );
+    // => [ 'one', 'two' ]
+}
+
+var fcns = [ foo, bar ];
+
+parallel( fcns, done );
+```
+
+</section>
+
+<!-- /.examples -->
+
+<!-- Section to include cited references. If references are included, add a horizontal rule *before* the section. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
+
+<section class="references">
+
+</section>
+
+<!-- /.references -->
+
+<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
+
+<section class="related">
+
+</section>
+
+<!-- /.related -->
+
+<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
+
+<section class="links">
+
+</section>
+
+<!-- /.links -->

lib/node_modules/@stdlib/utils/async/parallel/benchmark/benchmark.factory.js

@@ -0,0 +1,84 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2024 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+// MODULES //
+
+var bench = require( '@stdlib/bench' );
+var pkg = require( './../package.json' ).name;
+var factory = require( './../lib/factory.js' );
+
+
+// MAIN //
+
+bench( pkg+':factory', function benchmark( b ) {
+	var parallel;
+	var arr;
+	var i;
+
+	function one( resolve ) {
+		setTimeout( onTimeout, 0 );
+		function onTimeout() {
+			resolve( null, 'one' );
+		}
+	}
+
+	function two( resolve ) {
+		setTimeout( onTimeout, 0 );
+		function onTimeout() {
+			resolve( null, 'two' );
+		}
+	}
+
+	function three( resolve ) {
+		setTimeout( onTimeout, 0 );
+		function onTimeout() {
+			resolve( null, 'three' );
+		}
+	}
+
+	function four( resolve ) {
+		setTimeout( onTimeout, 0 );
+		function onTimeout() {
+			resolve( null, 'four' );
+		}
+	}
+
+	arr = [ one, two, three, four ];
+
+	parallel = factory( arr, next );
+
+	i = 0;
+	b.tic();
+
+	return next();
+
+	function next( error ) {
+		i += 1;
+		if ( error ) {
+			b.fail( 'should not return an error' );
+		}
+		if ( i <= b.iterations ) {
+			return parallel();
+		}
+		b.toc();
+		b.pass( 'benchmark finished' );
+		b.end();
+	}
+});