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Use SimpleQueue in WritableStream implementation
Split out Queue into a separate file from ReadableStream and rename is SimpleQueue to reduce the risk of name collisions on the binding object. Add a peek() method as it is needed by WritableStream. Modify WritableStream to use SimpleQueue. BUG=681493 Review-Url: https://codereview.chromium.org/2752133003 Cr-Commit-Position: refs/heads/master@{#458324}
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,91 @@ | ||
| // Copyright 2017 The Chromium Authors. All rights reserved. | ||
| // Use of this source code is governed by a BSD-style license that can be | ||
| // found in the LICENSE file. | ||
|
|
||
| // Queue implementation used by ReadableStream and WritableStream. | ||
|
|
||
| (function(global, binding, v8) { | ||
| 'use strict'; | ||
|
|
||
| // Simple queue structure. Avoids scalability issues with using | ||
| // InternalPackedArray directly by using multiple arrays in a linked list and | ||
| // keeping the array size bounded. | ||
| const QUEUE_MAX_ARRAY_SIZE = 16384; | ||
| class SimpleQueue { | ||
| constructor() { | ||
| this.front = { | ||
| elements: new v8.InternalPackedArray(), | ||
| next: undefined, | ||
| }; | ||
| this.back = this.front; | ||
| // The cursor is used to avoid calling InternalPackedArray.shift(). | ||
| this.cursor = 0; | ||
| this.size = 0; | ||
| } | ||
|
|
||
| get length() { | ||
| return this.size; | ||
| } | ||
|
|
||
| push(element) { | ||
| ++this.size; | ||
| if (this.back.elements.length === QUEUE_MAX_ARRAY_SIZE) { | ||
| const oldBack = this.back; | ||
| this.back = { | ||
| elements: new v8.InternalPackedArray(), | ||
| next: undefined, | ||
| }; | ||
| oldBack.next = this.back; | ||
| } | ||
| this.back.elements.push(element); | ||
| } | ||
|
|
||
| shift() { | ||
| // assert(this.size > 0); | ||
| --this.size; | ||
| if (this.front.elements.length === this.cursor) { | ||
| // assert(this.cursor === QUEUE_MAX_ARRAY_SIZE); | ||
| // assert(this.front.next !== undefined); | ||
| this.front = this.front.next; | ||
| this.cursor = 0; | ||
| } | ||
| const element = this.front.elements[this.cursor]; | ||
| // Permit shifted element to be garbage collected. | ||
| this.front.elements[this.cursor] = undefined; | ||
| ++this.cursor; | ||
|
|
||
| return element; | ||
| } | ||
|
|
||
| forEach(callback) { | ||
| let i = this.cursor; | ||
| let node = this.front; | ||
| let elements = node.elements; | ||
| while (i !== elements.length || node.next !== undefined) { | ||
| if (i === elements.length) { | ||
| // assert(node.next !== undefined); | ||
| // assert(i === QUEUE_MAX_ARRAY_SIZE); | ||
| node = node.next; | ||
| elements = node.elements; | ||
| i = 0; | ||
| } | ||
| callback(elements[i]); | ||
| ++i; | ||
| } | ||
| } | ||
|
|
||
| // Return the element that would be returned if shift() was called now, | ||
| // without modifying the queue. | ||
| peek() { | ||
| // assert(this.size > 0); | ||
| if (this.front.elements.length === this.cursor) { | ||
| // assert(this.cursor === QUEUE_MAX_ARRAY_SIZE) | ||
| // assert(this.front.next !== undefined); | ||
| return this.front.next.elements[0]; | ||
| } | ||
| return this.front.elements[this.cursor]; | ||
| } | ||
| } | ||
|
|
||
| binding.SimpleQueue = SimpleQueue; | ||
| }); |
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