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node_modules/cassandra-driver/lib/stream-id-stack.js
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node_modules/cassandra-driver/lib/stream-id-stack.js
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/*
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* Copyright DataStax, Inc.
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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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const types = require('./types');
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/**
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* Group size
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* @type {number}
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*/
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const groupSize = 128;
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/**
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* Number used to right shift ids to allocate them into groups
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* @const
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* @type {number}
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*/
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const shiftToGroup = 7;
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/**
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* Amount of groups that can be released per time
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* If it grows larger than 4 groups (128 * 4), groups can be released
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* @const
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* @type {number}
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*/
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const releasableSize = 4;
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/**
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* 32K possible stream ids depending for protocol v3 and above
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* @const
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* @type {number}
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*/
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const maxGroupsFor2Bytes = 256;
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/**
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* Delay used to check if groups can be released
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* @const
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* @type {number}
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*/
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const defaultReleaseDelay = 5000;
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/**
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* Represents a queue of ids from 0 to maximum stream id supported by the protocol version.
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* Clients can dequeue a stream id using {@link StreamIdStack#shift()} and enqueue (release) using
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* {@link StreamIdStack#push()}
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*/
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class StreamIdStack {
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/**
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* Creates a new instance of StreamIdStack.
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* @param {number} version Protocol version
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* @constructor
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*/
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constructor(version) {
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//Ecmascript Number is 64-bit double, it can be optimized by the engine into a 32-bit int, but nothing below that.
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//We try to allocate as few as possible in arrays of 128
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this.currentGroup = generateGroup(0);
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this.groupIndex = 0;
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this.groups = [this.currentGroup];
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this.releaseTimeout = null;
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this.setVersion(version);
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/**
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* Returns the amount of ids currently in use
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* @member {number}
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*/
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this.inUse = 0;
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this.releaseDelay = defaultReleaseDelay;
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}
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/**
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* Sets the protocol version
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* @param {Number} version
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*/
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setVersion(version) {
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//128 or 32K stream ids depending on the protocol version
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this.maxGroups = types.protocolVersion.uses2BytesStreamIds(version) ? maxGroupsFor2Bytes : 1;
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}
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/**
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* Dequeues an id.
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* Similar to {@link Array#pop()}.
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* @returns {Number} Returns an id or null
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*/
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pop() {
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let id = this.currentGroup.pop();
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if (typeof id !== 'undefined') {
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this.inUse++;
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return id;
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}
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//try to use the following groups
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while (this.groupIndex < this.groups.length - 1) {
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//move to the following group
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this.currentGroup = this.groups[++this.groupIndex];
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//try dequeue
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id = this.currentGroup.pop();
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if (typeof id !== 'undefined') {
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this.inUse++;
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return id;
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}
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}
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return this._tryCreateGroup();
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}
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/**
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* Enqueue an id for future use.
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* Similar to {@link Array#push()}.
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* @param {Number} id
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*/
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push(id) {
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this.inUse--;
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const groupIndex = id >> shiftToGroup;
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const group = this.groups[groupIndex];
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group.push(id);
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if (groupIndex < this.groupIndex) {
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//Set the lower group to be used to dequeue from
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this.groupIndex = groupIndex;
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this.currentGroup = group;
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}
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this._tryIssueRelease();
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}
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/**
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* Clears all timers
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*/
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clear() {
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if (this.releaseTimeout) {
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clearTimeout(this.releaseTimeout);
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this.releaseTimeout = null;
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}
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}
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/**
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* Tries to create an additional group and returns a new id
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* @returns {Number} Returns a new id or null if it's not possible to create a new group
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* @private
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*/
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_tryCreateGroup() {
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if (this.groups.length === this.maxGroups) {
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//we can have an additional group
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return null;
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}
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//Add a new group at the last position
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this.groupIndex = this.groups.length;
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//Using 128 * groupIndex as initial value
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this.currentGroup = generateGroup(this.groupIndex << shiftToGroup);
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this.groups.push(this.currentGroup);
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this.inUse++;
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return this.currentGroup.pop();
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}
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_tryIssueRelease() {
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if (this.releaseTimeout || this.groups.length <= releasableSize) {
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//Nothing to release or a release delay has been issued
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return;
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}
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this.releaseTimeout = setTimeout(() => this._releaseGroups(), this.releaseDelay);
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}
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_releaseGroups() {
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let counter = 0;
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let index = this.groups.length - 1;
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//only release up to n groups (n = releasable size)
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//shrink back up to n groups not all the way up to 1
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while (counter++ < releasableSize && this.groups.length > releasableSize && index > this.groupIndex) {
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if (this.groups[index].length !== groupSize) {
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//the group is being used
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break;
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}
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this.groups.pop();
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index--;
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}
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this.releaseTimeout = null;
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//Issue next release if applies
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this._tryIssueRelease();
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}
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}
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function generateGroup(initialValue) {
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const arr = new Array(groupSize);
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const upperBound = initialValue + groupSize - 1;
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for (let i = 0; i < groupSize; i++) {
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arr[i] = upperBound - i;
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}
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return arr;
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}
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module.exports = StreamIdStack;
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