137 lines
3.4 KiB
JavaScript
137 lines
3.4 KiB
JavaScript
/**
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* @license Apache-2.0
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*
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* Copyright (c) 2018 The Stdlib Authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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'use strict';
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// MODULES //
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var logger = require( 'debug' );
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// VARIABLES //
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var debug = logger( 'any-by-async:limit' );
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// MAIN //
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/**
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* Invokes a predicate function once for each element in a collection, limiting the number of concurrently pending functions.
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*
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* @private
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* @param {Collection} collection - input collection
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* @param {Options} opts - function options
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* @param {*} [opts.thisArg] - execution context
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* @param {PositiveInteger} [opts.limit] - maximum number of pending function invocations
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* @param {Function} predicate - predicate function
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* @param {Callback} done - function to invoke upon completion or upon encountering an error
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* @returns {void}
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*/
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function limit( collection, opts, predicate, done ) {
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var maxIndex;
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var count;
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var flg;
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var lim;
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var len;
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var idx;
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var i;
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len = collection.length;
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debug( 'Collection length: %d', len );
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if ( len === 0 ) {
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debug( 'Finished processing a collection.' );
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return done( null, false );
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}
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if ( len < opts.limit ) {
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lim = len;
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} else {
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lim = opts.limit;
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}
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debug( 'Concurrency limit: %d', lim );
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debug( 'Number of arguments: %d', predicate.length );
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maxIndex = len - 1;
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count = 0;
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idx = -1;
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for ( i = 0; i < lim; i++ ) {
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// This guard is necessary to protect against synchronous functions which exhaust all collection elements...
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if ( idx < maxIndex ) {
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next(); // eslint-disable-line callback-return
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}
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}
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/**
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* Callback to invoke a provided function for the next element in a collection.
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*
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* @private
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*/
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function next() {
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idx += 1;
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debug( 'Collection element %d: %s.', idx, JSON.stringify( collection[ idx ] ) );
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if ( predicate.length === 2 ) {
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predicate.call( opts.thisArg, collection[ idx ], clbk );
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} else if ( predicate.length === 3 ) {
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predicate.call( opts.thisArg, collection[ idx ], idx, clbk );
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} else {
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predicate.call( opts.thisArg, collection[ idx ], idx, collection, clbk ); // eslint-disable-line max-len
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}
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}
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/**
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* Callback invoked once a provided function finishes processing a collection element.
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*
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* @private
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* @param {*} [error] - error
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* @param {*} [result] - test result
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* @returns {void}
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*/
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function clbk( error, result ) {
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if ( flg ) {
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// Prevent further processing of collection elements:
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return;
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}
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if ( error ) {
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flg = true;
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debug( 'Encountered an error: %s', error.message );
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return done( error );
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}
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count += 1;
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debug( 'Processed %d of %d collection elements.', count, len );
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debug( 'Test result: %s', !!result );
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if ( result && !flg ) {
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flg = true;
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debug( 'Finished processing a collection.' );
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return done( null, true );
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}
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if ( idx < maxIndex ) {
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return next();
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}
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if ( count === len ) {
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debug( 'Finished processing a collection.' );
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return done( null, false );
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}
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}
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}
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// EXPORTS //
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module.exports = limit;
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