Press n or j to go to the next uncovered block, b, p or k for the previous block.
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* @license Apache-2.0
*
* Copyright (c) 2018 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 logger = require( 'debug' );
// VARIABLES //
var debug = logger( 'map-function-async:limit' );
// MAIN //
/**
* Invokes a function `n` times, limiting the number of concurrently pending invocations, and returns an array of accumulated function return values.
*
* @private
* @param {NonNegativeInteger} n - number of function invocations
* @param {Options} opts - function options
* @param {*} [opts.thisArg] - execution context
* @param {PositiveInteger} [opts.limit] - maximum number of pending function invocations
* @param {Function} fcn - function to invoke
* @param {Callback} done - function to invoke upon completion or upon encountering an error
* @returns {void}
*/
function limit( n, opts, fcn, done ) {
var count;
var flg;
var out;
var lim;
var idx;
var m;
var i;
debug( 'Number of invocations: %d', n );
// Note: we explicitly preallocate in order to facilitate inserting a function result into its associated output array index. This means we do not ensure "fast" elements for large output arrays.
out = new Array( n );
if ( n === 0 ) {
debug( 'Finished invoking a function.' );
return done( null, out );
}
if ( n < opts.limit ) {
lim = n;
} else {
lim = opts.limit;
}
debug( 'Concurrency limit: %d', lim );
count = 0;
idx = -1;
m = n - 1;
for ( i = 0; i < lim; i++ ) {
// This guard is necessary to protect against synchronous functions which exhaust all invocations...
if ( idx < m ) {
next(); // eslint-disable-line node/callback-return
}
}
/**
* Callback to process the next function invocation.
*
* @private
*/
function next() {
var j;
idx += 1;
j = idx;
debug( 'Invocation number: %d', j );
fcn.call( opts.thisArg, j, cb );
/**
* Callback invoked once a provided function completes.
*
* @private
* @param {*} [error] - error
* @param {*} [result] - result
* @returns {void}
*/
function cb( error, result ) {
if ( flg ) {
// Prevent further invocations:
return;
}
if ( error ) {
flg = true;
return clbk( error );
}
out[ j ] = result;
clbk();
}
}
/**
* Callback invoked once ready to process the next invocation.
*
* @private
* @param {*} [error] - error
* @returns {void}
*/
function clbk( error ) {
if ( error ) {
debug( 'Encountered an error: %s', error.message );
return done( error );
}
count += 1;
debug( 'Completed invocation %d of %d.', count, n );
if ( idx < m ) {
return next();
}
if ( count === n ) {
debug( 'Finished invoking a function.' );
return done( null, out );
}
}
}
// EXPORTS //
module.exports = limit;
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