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parallel-transform
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index.js
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var Transform = require('readable-stream').Transform; var inherits = require('inherits'); var cyclist = require('cyclist'); var util = require('util'); var ParallelTransform = function(maxParallel, opts, ontransform) { if (!(this instanceof ParallelTransform)) return new ParallelTransform(maxParallel, opts, ontransform); if (typeof maxParallel === 'function') { ontransform = maxParallel; opts = null; maxParallel = 1; } if (typeof opts === 'function') { ontransform = opts; opts = null; } if (!opts) opts = {}; if (!opts.highWaterMark) opts.highWaterMark = Math.max(maxParallel, 16); if (opts.objectMode !== false) opts.objectMode = true; Transform.call(this, opts); this._maxParallel = maxParallel; this._ontransform = ontransform; this._destroyed = false; this._flushed = false; this._ordered = opts.ordered !== false; this._buffer = this._ordered ? cyclist(maxParallel) : []; this._top = 0; this._bottom = 0; this._ondrain = null; }; inherits(ParallelTransform, Transform); ParallelTransform.prototype.destroy = function() { if (this._destroyed) return; this._destroyed = true; this.emit('close'); }; ParallelTransform.prototype._transform = function(chunk, enc, callback) { var self = this; var pos = this._top++; this._ontransform(chunk, function(err, data) { if (self._destroyed) return; if (err) { self.emit('error', err); self.push(null); self.destroy(); return; } if (self._ordered) { self._buffer.put(pos, (data === undefined || data === null) ? null : data); } else { self._buffer.push(data); } self._drain(); }); if (this._top - this._bottom < this._maxParallel) return callback(); this._ondrain = callback; }; ParallelTransform.prototype._flush = function(callback) { this._flushed = true; this._ondrain = callback; this._drain(); }; ParallelTransform.prototype._drain = function() { if (this._ordered) { while (this._buffer.get(this._bottom) !== undefined) { var data = this._buffer.del(this._bottom++); if (data === null) continue; this.push(data); } } else { while (this._buffer.length > 0) { var data = this._buffer.pop(); this._bottom++; if (data === null) continue; this.push(data); } } if (!this._drained() || !this._ondrain) return; var ondrain = this._ondrain; this._ondrain = null; ondrain(); }; ParallelTransform.prototype._drained = function() { var diff = this._top - this._bottom; return this._flushed ? !diff : diff < this._maxParallel; }; module.exports = ParallelTransform;