Go新提案:go vet新增检测项,当在defer后直接使用time.Since时给出提示

留言

cmd/vet: time.Since should not be used in defer statement

如 go vet中的那些检测项 13. defers中介绍

report common mistakes in defer statements

当 defer 语句导致非延迟调用 time 时，defer 分析器会报告诊断。因为，经验表明这几乎总是一个错误。 例如：

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//	start := time.Now()
//	...
//	defer recordLatency(time.Since(start)) // error: call to time.Since is not deferred
//
// The correct code is:
//
//	defer func() { recordLatency(time.Since(start)) }()

即 

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package main

import (
	"fmt"
	"time"
)

func main() {

	start := time.Now()
	fmt.Println("当前时间:", start)

	defer recordLatency(time.Since(start))

	time.Sleep(3 * time.Second)

}

func recordLatency(duration time.Duration) {

	fmt.Println("共耗时:", duration)

}

输出并不是预期的3s多，而是200多µs

这是因为time.Since会立刻计算，不会等defer执行时才算

上面这段代码，加defer和不加defer效果一样


正确的写法如下:

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package main

import (
	"fmt"
	"time"
)

func main() {

	start := time.Now()
	fmt.Println("当前时间:", start)

	defer func() {
		recordLatency(time.Since(start))
	}()

	time.Sleep(3 * time.Second)

}

func recordLatency(duration time.Duration) {

	fmt.Println("共耗时:", duration)

}

输出：

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当前时间: 2023-07-25 16:44:26.90604 +0800 CST m=+0.000169751
共耗时: 3.001356959s

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