Node.js
代码var http = require('http');
http.createServer(function (request, response) {
var num = 0
for (var i = 1; i < 5900000000; i++) {
num += i
}
response.end('Hello' + num);
}).listen(8888);
nodemon
启动服务,用time curl
调用这个接口7.xxs
耗时CPU
使用当时很高,差不多打到100%
了.但是我后面发现不是这个问题.CPU
问题,看内存消耗占用。var http = require('http');
http
.createServer(function(request, response) {
console.log(request.url, 'url');
let used = process.memoryUsage().heapUsed / 1024 / 1024;
console.log(
`The script uses approximately ${Math.round(used * 100) / 100} MB`,
'start',
);
console.time('测试');
let num = 0;
for (let i = 1; i < 5900000000; i++) {
num += i;
}
console.timeEnd('测试');
used = process.memoryUsage().heapUsed / 1024 / 1024;
console.log(
`The script uses approximately ${Math.round(used * 100) / 100} MB`,
'end',
);
response.end('Hello' + num);
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})
.listen(8888);
CPU
都正常5.9亿次
)var a = 'java'
var b = a + 'script'
* 只连接100个以下的字符串建议用这种方法最方便
var arr = ['hello','java','script']
var str = arr.join("")
var a = 'java'
var b = `hello ${a}script`
var a = 'java'
var b = 'script'
var str = a.concat(b)
function StringConnect(){
this.arr = new Array()
}
StringConnect.prototype.append = function(str) {
this.arr.push(str)
}
StringConnect.prototype.toString = function() {
return this.arr.join("")
}
var mystr = new StringConnect()
mystr.append("abc")
mystr.append("def")
mystr.append("g")
var str = mystr.toString()
join
方式(此时循环5.9
亿次)var http = require('http');
http
.createServer(function(request, response) {
console.log(request.url, 'url');
let used = process.memoryUsage().heapUsed / 1024 / 1024;
console.log(
`The script uses approximately ${Math.round(used * 100) / 100} MB`,
'start',
);
console.time('测试');
let num = 0;
for (let i = 1; i < 590000000; i++) {
num += i;
}
const arr = ['Hello'];
arr.push(num);
console.timeEnd('测试');
used = process.memoryUsage().heapUsed / 1024 / 1024;
console.log(
`The script uses approximately ${Math.round(used * 100) / 100} MB`,
'end',
);
response.end(arr.join(''));
})
.listen(8888);
注意此时是5.9亿次循环
)《javascript高级程序设计》
中,有一段关于字符串特点的描述,原文大概如下:ECMAScript
中的字符串是不可变的,也就是说,字符串一旦创建,他们的值就不能改变。要改变某个变量的保存的的字符串,首先要销毁原来的字符串,然后再用另外一个包含新值的字符串填充该变量+
直接拼接字符串自然会对性能产生一些影响,因为字符串是不可变的,在操作的时候会产生临时字符串副本,+
操作符需要消耗时间,重新赋值分配内存需要消耗时间。var http = require('http');
http
.createServer(function(request, response) {
console.log(request.url, 'url');
let used = process.memoryUsage().heapUsed / 1024 / 1024;
console.log(
`The script uses approximately ${Math.round(used * 100) / 100} MB`,
'start',
);
console.time('测试');
let num = 0;
for (let i = 1; i < 5900000000; i++) {
// num++;
}
const arr = ['Hello'];
// arr[1] = num;
console.timeEnd('测试');
used = process.memoryUsage().heapUsed / 1024 / 1024;
console.log(
`The script uses approximately ${Math.round(used * 100) / 100} MB`,
'end',
);
response.end('hello');
})
.listen(8888);
for
循环的耗时不一致var http = require('http');
http
.createServer(function(request, response) {
console.log(request.url, 'url');
let used = process.memoryUsage().heapUsed / 1024 / 1024;
console.log(
`The script uses approximately ${Math.round(used * 100) / 100} MB`,
'start',
);
let num = 0;
console.time('测试');
for (let i = 1; i < 5900000000; i++) {
// num++;
}
console.timeEnd('测试');
const arr = ['Hello'];
// arr[1] = num;
used = process.memoryUsage().heapUsed / 1024 / 1024;
console.log(
`The script uses approximately ${Math.round(used * 100) / 100} MB`,
'end',
);
response.end('hello');
})
.listen(8888);
for
循环内部的i++
其实就是变量不断的重新赋值覆盖40亿次
跟50亿次
的区别,差距很大,40亿次的for循环
,都是稳定的,但是50亿次
就不稳定了.Node.js
的EventLoop
:CPU
使用情况60亿
次的循环,像有使用多进程异步计算的,但是本质上没有解决这部分循环代码的调用耗时。for
循环:var http = require('http');
http
.createServer(function(request, response) {
console.log(request.url, 'url');
let used = process.memoryUsage().heapUsed / 1024 / 1024;
console.log(
`The script uses approximately ${Math.round(used * 100) / 100} MB`,
'start',
);
let num = 0;
console.time('测试');
for (let i = 1; i < 600000; i++) {
num++;
for (let j = 0; j < 10000; j++) {
num++;
}
}
console.timeEnd('测试');
const arr = ['Hello'];
console.log(num, 'num');
arr[1] = num;
used = process.memoryUsage().heapUsed / 1024 / 1024;
console.log(
`The script uses approximately ${Math.round(used * 100) / 100} MB`,
'end',
);
response.end(arr.join(''));
})
.listen(8888);
60亿次
循环总共:+
方式拼接字符串var http = require('http');
http
.createServer(function(request, response) {
console.log(request.url, 'url');
let used = process.memoryUsage().heapUsed / 1024 / 1024;
console.log(
`The script uses approximately ${Math.round(used * 100) / 100} MB`,
'start',
);
let num = 0;
console.time('测试');
for (let i = 1; i < 600000; i++) {
num++;
for (let j = 0; j < 10000; j++) {
num++;
}
}
console.timeEnd('测试');
// const arr = ['Hello'];
console.log(num, 'num');
// arr[1] = num;
used = process.memoryUsage().heapUsed / 1024 / 1024;
console.log(
`The script uses approximately ${Math.round(used * 100) / 100} MB`,
'end',
);
response.end(`Hello` + num);
})
.listen(8888);
Node.js
的运行耗时是稳定,但是如果是循环次数过多,那么就会出现刚才那种情况,阻塞严重,耗时不一样。CPU
有一些关系,因为top
查看一直是在升高i
的值到60亿
,还要不断更新num
的值60亿
,内存使用会不断上升,最终出现两份60亿
的数据,然后再回收。(因为GC自动垃圾回收,一样会阻塞主线程
,多次接口调用后,CPU
占用也会升高)for
循环拆解后: for (let i = 1; i < 60000; i++) {
num++;
for (let j = 0; j < 100000; j++) {
num++;
}
}
num
到60亿
即可,解决了这个问题。如果是异步的业务场景,也可以用多进程参与解决超大计算量问题,今天这里就不重复介绍了