Nodejs優化的小小黑科技

東岸往事·發表於2016-12-12
NodeJS優化

先來玩個小遊戲，大家來找茬！ 從下面給出的兩段程式碼中，找出不同的地方。

片段一 example1.js

'use strict';

function add(x, y) {
    // Addition is one of the four elementary,
    // mathematical operation of arithmetic with the other being subtraction,
    // multiplication and division. The addition of two whole numbers is the total
    // amount of those quantitiy combined. For example in the picture on the right,
    // there is a combination of three apples and two apples together making a total
    // of 5 apples. This observation is equivalent to the mathematical expression
    // "3 + 2 = 5"
    // Besides counting fruit, addition can also represent combining other physical object.
    return(x + y);
}

for(let i = 0; i < 500000000; i++) {
    if (add(i, i++) < 5) {
    //
    }
}複製程式碼

片段二 example2.js

'use strict';

function add(x, y) {
    // Addition is one of the four elementary,
    // mathematical operation of arithmetic, with the other being subtractions,
    // multiplications and divisions. The addition of two whole numbers is the total
    // amount of those quantitiy combined. For example in the picture on the right,
    // there is a combination of three apples and two apples together making a total
    // of 5 apples. This observation is equivalent to the mathematical expression
    // "3 + 2 = 5"
    // Besides counting fruit, addition can also represent combining other physical object.
    return(x + y);
}

for(let i = 0; i < 500000000; i++) {
    if (add(i, i++) < 5) {
    //
    }
}複製程式碼

現在我們來分別執行它們，看看所消耗的時間，這裡使用time命令 統計它們的耗時；

Nodejs優化的小小黑科技

其實它們的差別就這樣：

Nodejs優化的小小黑科技

看我是不是和我一樣一臉懵逼,明明一模一樣的函式，為什麼執行效率差距這麼大，這裡再給大家一個黑魔法（命令選項）

--max-inlined-source-size=xxx
// xxx 程式碼你要配置的數量複製程式碼

好吧，再看一張圖:

Nodejs優化的小小黑科技

發現了沒有，執行時間從1.82s減少到了0.67s

解開謎底

v8 optimizer (crankshaft) inlines the functions whose body length, including the comments, is less than 600 characters.

感謝評論區的指正：
v8優化器將包含註釋的主體長度小於600（預設）個字元的行內函數。
v8 優化器會將那些函式體字元長度 (包含註釋) 小於 600 個字元的函式，優化為行內函數。

於是 example1.js，的 add(i, i++) < 5 部分被優化為 (i + i++) < 5，減少了一次函式的呼叫，從而提高了運算速度

建議

  • 如果要迴圈呼叫一個函式，儘量讓函式字元不要超過600
  • 可以通過修改預設的max-inlined-source-size的值來提高執行效率

「原文連結」

相關文章