fix duration of mosaic conversion

[MohammadAlavi1986]

t1 (end time) must be assigned to after we have received converted image from the channel

	t1 := time.Now()
	images := map[string]string{
		"original": originalStr,
		"mosaic":   <- c,
		"duration": fmt.Sprintf("%v ", t1.Sub(t0)),
	}

mus change to:

        mosaicStr := <- c
	t1 := time.Now()
	images := map[string]string{
		"original": originalStr,
		"mosaic":   mosaicStr,
		"duration": fmt.Sprintf("%v ", t1.Sub(t0)),
	}

[hyzgh]

I encounter this problem too. The fixed version works correctly. But I couldn't figure out the reason. Do you know anything about the reason?

[MohammadAlavi1986]

@hyzgh when the channel is read if the channel is not ready the receiver will be blocked until the channel is ready that's the reason why we should assign time.Now() to t1 only after we have read the channel content successfully but the original version assigns to t1 before it reads the channel.

[hyzgh]

@AureaMohammadAlavi If we read the channel when we initial the map, it will be blocked too. I have written a test to prove it.

package main

import (
	"fmt"
	"time"
)

func getSlow() chan int {
	d := make(chan int)
	go func() {
		time.Sleep(1*time.Second)
		d <- 42
	}()
	return d
}

func main() {
	t0 := time.Now()
	m := map[string]interface{}{
		"mosaic": <-getSlow(),
		"duration": time.Now().Sub(t0),
	}
	fmt.Println(m)
}
// output: map[duration:1.000127088s mosaic:42]

[MohammadAlavi1986]

@hyzgh Yes it will be blocked and that's why we should only calculate the duration after we've read from the channel but in the author's code the duration is calculated (now is assigned to t1) before reading from the channel.

	t1 := time.Now()
	images := map[string]string{
		"original": originalStr,
		"mosaic":   <- c,
		"duration": fmt.Sprintf("%v ", t1.Sub(t0)),
	}

In your sample code you calculate duration after reading from the channel and that's correct.

[hyzgh]

I got it. Thank you!

On Fri, Jun 26, 2020 at 1:46 AM Mohammad Alavi [email protected] wrote:

@hyzgh https://github.com/hyzgh Yes it will be blocked and that's why we should only calculate the duration after we've read from the channel but in the author's code the duration is calculated (now is assigned to t1) before reading from the channel.

t1 := time.Now() images := map[string]string{ "original": originalStr, "mosaic": <- c, "duration": fmt.Sprintf("%v ", t1.Sub(t0)), }

In your sample code you calculate duration after reading from the channel and that's correct.

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