node-idgen/lib/idGenerator.js

generator 15 bit integers id for nodejs.

/*****************************************************
 * Author  : Administrator
 * Version : 1.0
 * Date    :  2015/2/2
 ****************************************************/
var util = require("util");
var TWEPOCH = 1400485784045;
var WORKERIDBITS = 6;
var MAXWORKERID = -1 ^ (-1 << WORKERIDBITS);
var SEQUENCEBITS = 6;
var WORKERIDSHIFT = SEQUENCEBITS;
var TIMESTAMPLEFTSHIFT = SEQUENCEBITS + WORKERIDBITS;
var SEQUENCEMASK = -1 ^ (-1 << SEQUENCEBITS);

function IdGenerator() {
	var workerId = (process.pid % MAXWORKERID);
	if (workerId > MAXWORKERID || workerId < 0) {
		throw new Error(util.format("worker Id can't be greater than %d or less than 0", MAXWORKERID));

	}
	this.workerId = workerId;
	this.lastTimestamp = -1;
	this.sequence = 0;
}

IdGenerator.prototype.nextId = function () {
	var timestamp = new Date().getTime();
	if (this.lastTimestamp == timestamp) {
		this.sequence = (this.sequence + 1) & SEQUENCEMASK;
		if (this.sequence == 0) {
			timestamp = tilNextMillis(this.lastTimestamp);
		}
	} else {
		this.sequence = 0;
	}
	if (timestamp < this.lastTimestamp) {
		throw new Error(util.format("Clock moved backwards. Refusing to generate id for %d milliseconds",
				this.lastTimestamp - timestamp));
	}

	this.lastTimestamp = timestamp;
	return leftShift((timestamp - TWEPOCH), TIMESTAMPLEFTSHIFT) + (this.workerId << WORKERIDSHIFT) + this.sequence;
};

// 将leftNum转二进制，加bits个0（相当左移运算），再转回10进制
// Will be converted to binary leftNum, followed by bits' 0 (equivalent to the left shift operation), and then back to 10 decimal
function leftShift(leftNum, bits) {
	return parseInt(('' + parseInt(leftNum).toString(2) + (new Array(bits + 1).join('0'))), 2);
}

function tilNextMillis(lastTimestamp) {
	var timestamp = new Date().getTime();
	while (timestamp <= lastTimestamp) {
		timestamp = new Date().getTime();
	}
	return timestamp;
}

module.exports = exports = IdGenerator;