常见的time duration问题

invalid operation: num * time.Second (mismatched types int64 and time.Duration)

invalid operation: num * time.Second (mismatched types int and time.Duration)

比如用math/rand得到一个随机数，然后time.sleep()等待…

num := rand.Int31n(10)
time.sleep(num * time.Second)

那么会遇到下面的问题:

# command-line-arguments
./lock.go:88: invalid operation: int(DefaultTimeout) * time.Second (mismatched types int and time.Duration)

解决的方法:

使用time.Duration转换类型

num := rand.Int31n(10)
time.Sleep(time.Duration(num) * time.Second)

产生的原因:

sleep接收的参数为Duration类型

func Sleep(d Duration) ...

当我们要实现5秒时，方法为 5 * second，second又是1000 * Millisecond，而Millisecond又是1000 * Microsecond，Microsecond又是1000 * Nanosecond，Nanosecond为一个纳秒，他的类型就是Duration。最后5秒拿到的数应该是 5,000,000,000数值

type Duration int64

const (
    Nanosecond Duration = 1    // 设为1个纳秒
    Microsecond = 1000 * Nanosecond
    Millisecond = 1000 * Microsecond
    Second = 1000 * Millisecond
    Minute = 60 * Second
    Hour = 60 * Minute
)

那么为什么我们可以直接使用 time.Sleep(5 * time.Second) ?

// xiaoru.cc

package main

import (
	"time"
)

func main() {
	time.Sleep(time.Duration(2) * time.Second)
	time.Sleep(3 * time.Second)
}

通过汇编分析可以看到golang已帮我优化了time.Duration的转换。

	0x005d 00093 (GOROOT/src/fmt/print.go:274)	MOVQ	CX, 16(SP)
	0x0062 00098 (GOROOT/src/fmt/print.go:274)	MOVQ	1, 24(SP)
	0x006b 00107 (GOROOT/src/fmt/print.go:274)	MOVQ	1, 32(SP)
	0x0074 00116 (GOROOT/src/fmt/print.go:274)	CALL	fmt.Fprintln(SB)
	0x0079 00121 (kk.go:10)	MOVQ	2000000000, (SP)
	0x0081 00129 (kk.go:10)	CALL	time.Sleep(SB)
	0x0086 00134 (kk.go:11)	MOVL3000000000, AX
	0x008b 00139 (kk.go:11)	MOVQ	AX, (SP)
	0x008f 00143 (kk.go:11)	CALL	time.Sleep(SB)
	0x0094 00148 (kk.go:13)	PCDATA	1,2