limit.js (3473B)
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( 'inmap-right-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 and iterating from right to left, and updates a collection in-place. 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 count; 47 var flg; 48 var lim; 49 var len; 50 var idx; 51 var i; 52 53 len = collection.length; 54 debug( 'Collection length: %d', len ); 55 56 if ( len === 0 ) { 57 debug( 'Finished processing a collection.' ); 58 return done(); 59 } 60 if ( len < opts.limit ) { 61 lim = len; 62 } else { 63 lim = opts.limit; 64 } 65 debug( 'Concurrency limit: %d', lim ); 66 debug( 'Number of arguments: %d', fcn.length ); 67 68 count = 0; 69 idx = len; 70 for ( i = 0; i < lim; i++ ) { 71 // This guard is necessary to protect against synchronous functions which exhaust all collection elements... 72 if ( idx > 0 ) { 73 next(); // eslint-disable-line callback-return 74 } 75 } 76 /** 77 * Callback to invoke a provided function for the next element in a collection. 78 * 79 * @private 80 */ 81 function next() { 82 var j; 83 idx -= 1; 84 j = idx; 85 debug( 'Collection element %d: %s.', j, JSON.stringify( collection[ j ] ) ); 86 if ( fcn.length === 2 ) { 87 fcn.call( opts.thisArg, collection[ j ], cb ); 88 } else if ( fcn.length === 3 ) { 89 fcn.call( opts.thisArg, collection[ j ], j, cb ); 90 } else { 91 fcn.call( opts.thisArg, collection[ j ], j, collection, cb ); 92 } 93 /** 94 * Callback invoked once a provided function finishes processing a collection element. 95 * 96 * @private 97 * @param {*} [error] - error 98 * @param {*} [result] - result 99 * @returns {void} 100 */ 101 function cb( error, result ) { 102 if ( flg ) { 103 // Prevent further processing of collection elements: 104 return; 105 } 106 if ( error ) { 107 flg = true; 108 return clbk( error ); 109 } 110 collection[ j ] = result; 111 clbk(); 112 } 113 } 114 115 /** 116 * Callback invoked once ready to process the next collection element. 117 * 118 * @private 119 * @param {*} [error] - error 120 * @returns {void} 121 */ 122 function clbk( error ) { 123 if ( error ) { 124 debug( 'Encountered an error: %s', error.message ); 125 return done( error ); 126 } 127 count += 1; 128 debug( 'Processed %d of %d collection elements.', count, len ); 129 if ( idx > 0 ) { 130 return next(); 131 } 132 if ( count === len ) { 133 debug( 'Finished processing a collection.' ); 134 return done(); 135 } 136 } 137 } 138 139 140 // EXPORTS // 141 142 module.exports = limit;