limit.js (3137B)
1 /** 2 * @license Apache-2.0 3 * 4 * Copyright (c) 2018 The Stdlib Authors. 5 * 6 * Licensed under the Apache License, Version 2.0 (the "License"); 7 * you may not use this file except in compliance with the License. 8 * You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 19 'use strict'; 20 21 // MODULES // 22 23 var logger = require( 'debug' ); 24 25 26 // VARIABLES // 27 28 var debug = logger( 'for-each-async:limit' ); 29 30 31 // MAIN // 32 33 /** 34 * Invokes a function once for each element in a collection, limiting the number of concurrently pending functions. 35 * 36 * @private 37 * @param {Collection} collection - input collection 38 * @param {Options} opts - function options 39 * @param {*} [opts.thisArg] - execution context 40 * @param {PositiveInteger} [opts.limit] - maximum number of pending function invocations 41 * @param {Function} fcn - function to invoke 42 * @param {Callback} done - function to invoke upon completion or upon encountering an error 43 * @returns {void} 44 */ 45 function limit( collection, opts, fcn, done ) { 46 var maxIndex; 47 var count; 48 var flg; 49 var lim; 50 var len; 51 var idx; 52 var i; 53 54 len = collection.length; 55 debug( 'Collection length: %d', len ); 56 57 if ( len === 0 ) { 58 debug( 'Finished processing a collection.' ); 59 return done(); 60 } 61 if ( len < opts.limit ) { 62 lim = len; 63 } else { 64 lim = opts.limit; 65 } 66 debug( 'Concurrency limit: %d', lim ); 67 debug( 'Number of arguments: %d', fcn.length ); 68 69 maxIndex = len - 1; 70 count = 0; 71 idx = -1; 72 for ( i = 0; i < lim; i++ ) { 73 // This guard is necessary to protect against synchronous functions which exhaust all collection elements... 74 if ( idx < maxIndex ) { 75 next(); // eslint-disable-line callback-return 76 } 77 } 78 79 /** 80 * Callback to invoke a provided function for the next element in a collection. 81 * 82 * @private 83 */ 84 function next() { 85 idx += 1; 86 debug( 'Collection element %d: %s.', idx, JSON.stringify( collection[ idx ] ) ); 87 if ( fcn.length === 2 ) { 88 fcn.call( opts.thisArg, collection[ idx ], clbk ); 89 } else if ( fcn.length === 3 ) { 90 fcn.call( opts.thisArg, collection[ idx ], idx, clbk ); 91 } else { 92 fcn.call( opts.thisArg, collection[ idx ], idx, collection, clbk ); 93 } 94 } 95 96 /** 97 * Callback invoked once a provided function finishes processing a collection element. 98 * 99 * @private 100 * @param {*} [error] - error 101 * @returns {void} 102 */ 103 function clbk( error ) { 104 if ( flg ) { 105 // Prevent further processing of collection elements: 106 return; 107 } 108 if ( error ) { 109 flg = true; 110 debug( 'Encountered an error: %s', error.message ); 111 return done( error ); 112 } 113 count += 1; 114 debug( 'Processed %d of %d collection elements.', count, len ); 115 if ( idx < maxIndex ) { 116 return next(); 117 } 118 if ( count === len ) { 119 debug( 'Finished processing a collection.' ); 120 return done(); 121 } 122 } 123 } 124 125 126 // EXPORTS // 127 128 module.exports = limit;