1. node.js 单线程的特点
node.js 以异步非阻塞单线程，作为其执行速度的保障。什么是非阻塞单线程？
举一个现实生活中的例子，我去巢大食堂打饭，我选择了A套餐，然后工作人员区为我配餐，我就在旁边等着直到阿姨叫号然后我取餐。这个过程是同步。
如果工作人员在为我配餐的同时，仍然可以接受排在我后面的同学的点餐，这样餐厅并没有因为我在等待A套餐而停止。这个过程是非阻塞。
如果我在阿姨为我配餐的同时，我去旁边小超市买了杯冷饮，等阿姨叫号时我再去取餐。这个过程就是异步非阻塞，同时阿姨叫号我去取餐的行为叫做回调。
- 高性能（不用考虑多线程间来回调用引起性能的损耗）
- 线程安全（不用担心同意变量会被多线程进行读写而造成程序的崩溃）
-
底层多线程
说node.js 是单线程其实也是不全面的，node.js 底层库会使用libuv调用多线程来处理I/O 操作。这就像食堂只有一个窗口，只能有按顺序一个个的接收点餐，但是后厨配菜的员工却有很多，他们各司其职保证出餐的速度。
如果服务器是多核且有充足的物理资源，如何充分发挥这些物理资源达到性能最大化。既食堂后厨有很多大师傅，一个窗口售卖的速度太慢，许多大师傅都是空闲的窗台。邪恶的资本家你们懂的？
2.如何通过多线程提高node.js 的性能
- cluster: 为了利用多核系统，用户有时会想启动一个 Node.js 进程的集群去处理负载。
const Koa = require('Koa');
const koaRouter = require('koa-router');
const app = new Koa();
const router = new koaRouter();
function fibo(n) {
return n > 1 ? fibo(n - 1) + fibo(n-2) : 1
}
app.use(router['routes']());
router.get('/', function(ctx, next) {
var result = fibo(35);
ctx.body = `${result}`;
});
if (!module.parent) {
app.listen(8080);
console.log(`Server was start.`);
}
通过ab 压力测试命令：
ab -c 20 -n 100 http://localhost:8080/
没有经过cluster 集群优化：
Server Software:
Server Hostname: localhost
Server Port: 8080
Document Path: /
Document Length: 8 bytes
Concurrency Level: 20
Time taken for tests: 13.569 seconds
Complete requests: 100
Failed requests: 0
Total transferred: 14300 bytes
HTML transferred: 800 bytes
Requests per second: 7.37 [#/sec] (mean)
Time per request: 2713.723 [ms] (mean)
Time per request: 135.686 [ms] (mean, across all concurrent requests)
Transfer rate: 1.03 [Kbytes/sec] received
Connection Times (ms)
min mean[+/-sd] median max
Connect: 0 0 0.2 0 1
Processing: 155 2465 622.9 2738 2762
Waiting: 153 2465 623.0 2737 2762
Total: 155 2465 622.8 2738 2762
Percentage of the requests served within a certain time (ms)
50% 2738
66% 2743
75% 2746
80% 2747
90% 2753
95% 2757
98% 2761
99% 2762
100% 2762 (longest request)
通过cluster 集群优化后：
const Koa = require('Koa');
const koaRouter = require('koa-router');
const numCpus = require('os').cpus().length;
const cluster = require('cluster');
const app = new Koa();
const router = new koaRouter();
if (cluster.isMaster) {
console.log(`${numCpus}`);
for (var index = 0; index < numCpus; index++) {
cluster.fork();
}
} else {
app.use(router['routes']());
router.get('/', function(ctx, next) {
var result = fibo(35);
ctx.body = `${result}`;
});
if (!module.parent) {
app.listen(8080);
console.log(`Server was start.`);
}
}
function fibo(n) {
return n > 1 ? fibo(n - 1) + fibo(n-2) : 1
}
通过ab 压力测试命令：
ab -c 20 -n 100 http://localhost:8080/
Server Software:
Server Hostname: localhost
Server Port: 8080
Document Path: /
Document Length: 8 bytes
Concurrency Level: 20
Time taken for tests: 6.513 seconds
Complete requests: 100
Failed requests: 0
Total transferred: 14300 bytes
HTML transferred: 800 bytes
Requests per second: 15.35 [#/sec] (mean)
Time per request: 1302.524 [ms] (mean)
Time per request: 65.126 [ms] (mean, across all concurrent requests)
Transfer rate: 2.14 [Kbytes/sec] received
Connection Times (ms)
min mean[+/-sd] median max
Connect: 0 0 0.5 0 2
Processing: 279 1198 258.7 1294 1335
Waiting: 279 1198 258.7 1294 1335
Total: 281 1198 258.3 1295 1335
Percentage of the requests served within a certain time (ms)
50% 1295
66% 1301
75% 1303
80% 1308
90% 1322
95% 1328
98% 1333
99% 1335
100% 1335 (longest request)
对比两次的测试结果：
优化后，
Requests per second （每秒处理的任务数） 由 7.37 提高到 15.35.
Time per request （每个用户的平均处理时间） 由 135.686 降低到 65.126
3. 如何通过多进程提高node.js 的性能
- Child Process 创建进程
main.js
const Koa = require('Koa');
const koaRouter = require('koa-router');
const fork = require('child_process').fork;
const app = new Koa();
const router = new koaRouter();
app.use(router['routes']());
router.get('/', function(ctx, next) {
var worker = fork('./work_fibo.js');
worker.on('message', function(m) {
if ('object' === typeof m && m.type === 'fibo') {
worker.kill();
ctx.body = m.result.toString();
}
});
worker.send({type: "fibo", num: 35}, (err) => {
console.log(`${err}`);
});
console.log(`${worker.pid}`);
});
if (!module.parent) {
app.listen(8080);
console.log(`Server was start.`);
}
work_fibo.js
var fibo = function fibo(n) {
return n > 1 ? fibo(n - 1) + fibo(n - 2) : 1;
}
process.on('message', function(m) {
if (typeof m === 'object' && m.type === 'fibo') {
var num = fibo(m.num);
process.send({type: 'fibo', result: num});
}
});
process.on('SIGHUP', function() {
process.exist();
});
通过ab 压力测试命令：
ab -c 20 -n 100 http://localhost:8080/
Server Software:
Server Hostname: localhost
Server Port: 8080
Document Path: /
Document Length: 9 bytes
Concurrency Level: 20
Time taken for tests: 3.619 seconds
Complete requests: 100
Failed requests: 0
Non-2xx responses: 100
Total transferred: 15100 bytes
HTML transferred: 900 bytes
Requests per second: 27.63 [#/sec] (mean)
Time per request: 723.764 [ms] (mean)
Time per request: 36.188 [ms] (mean, across all concurrent requests)
Transfer rate: 4.07 [Kbytes/sec] received
Connection Times (ms)
min mean[+/-sd] median max
Connect: 0 1 4.5 0 43
Processing: 21 611 270.7 650 1134
Waiting: 18 610 270.7 649 1132
Total: 22 612 270.2 652 1134
Percentage of the requests served within a certain time (ms)
50% 652
66% 744
75% 794
80% 835
90% 958
95% 1054
98% 1122
99% 1134
100% 1134 (longest request)
对比两次的测试结果：
优化后，
Requests per second （每秒处理的任务数） 由 7.37 提高到 15.35 最后通过进程优化后达到 27.63
Time per request （每个用户的平均处理时间） 由 135.686 降低到 65.126 最后通过进程优化后达到 36.188
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