Why not changing the mapping of the progress bar in gxui?

I wanted to use the Progress bar from gxui, but get not what I expected.
The example works as it should,but change it I did not succeed. Here is the code:

package main
import (
"fmt"
"io/ioutil"
"log"
"net/http"
"time"
"github.com/google/gxui"
"github.com/google/gxui/drivers/gl"
"github.com/google/gxui/math"
"github.com/google/gxui/samples/flags"
)
func appMain(driver gxui.Driver) {
theme := flags.CreateTheme(driver)
layout := theme.CreateLinearLayout()
layout.SetHorizontalAlignment(gxui.AlignCenter)
progressBar := theme.CreateProgressBar()
progressBar.SetDesiredSize(math.Size{W: 480, H: 60})
button := theme.CreateButton()
button.SetText("Start")
t0 := time.Now()
button.OnClick(func(gxui.MouseEvent) {
progressBar.SetTarget(100)
N := 100
for count := 0; count < N; count++ {
resp, err := http.Get("http://example.com")
if err != nil {
log.Fatal(err)
}
defer resp.Body.Close()
if count%10 == 0 {
go func() {
driver.Call(func() {
fmt.Println("Tuk")
progressBar.SetProgress(count * 100 / N)
})
}()
fmt.Println(count)
fmt.Println(ioutil.ReadAll(resp.Body))
fmt.Printf("Elapsed time: %v\n", time.Since(t0))
}
}
progressBar.SetProgress(50)
})
layout.AddChild(button)
layout.AddChild(progressBar)
window := theme.CreateWindow(500, 100, "Test")
window.SetScale(flags.DefaultScaleFactor)
window.AddChild(layout)
window.OnClose(driver.Terminate)
}
func main() {
gl.StartDriver(appMain)
}

Since I used goroutine, it is assumed that the output text will alternate, but all goroutine performed print only after the main thread.
What am I doing wrong and how to fix it?

1: https://github.com/google/gxui "gxui"
2: https://github.com/google/gxui/blob/master/samples/progress_bar/main.go "example"

The difference is that your goroutine enter the queue executing the UI routine, as written in the documentation:

> // Call queues f to be run on the UI go-routine, returning before f
> may have been called.

UI-routine executes a loop, so can not simultaneously handle the change
tape ProgressBar. To get the desired result, it is necessary run handling function in a separate goroutine. Modified code:

package main
import (
"fmt"
"io/ioutil"
"log"
"net/http"
"time"
"github.com/google/gxui"
"github.com/google/gxui/drivers/gl"
"github.com/google/gxui/math"
"github.com/google/gxui/samples/flags"
)
func appMain(driver gxui.Driver) {
theme := flags.CreateTheme(driver)
layout := theme.CreateLinearLayout()
layout.SetHorizontalAlignment(gxui.AlignCenter)
progressBar := theme.CreateProgressBar()
progressBar.SetDesiredSize(math.Size{W: 480, H: 60})
progressBar.SetTarget(100)
button := theme.CreateButton()
button.SetText("Start")
t0 := time.Now()
button.OnClick(func(gxui.MouseEvent) {
go func() {
N := 100
for count := 0; count < N; count++ {
resp, err := http.Get("http://example.com")
if err != nil {
log.Fatal(err)
}
defer resp.Body.Close()
driver.Call(func() {
progressBar.SetProgress(count * 100 / N)
})
fmt.Println(count)
fmt.Println(ioutil.ReadAll(resp.Body))
fmt.Printf("Elapsed time: %v\n", time.Since(t0))
}
progressBar.SetTarget(100)
}()
})
layout.AddChild(button)
layout.AddChild(progressBar)
window := theme.CreateWindow(500, 100, "Test")
window.SetScale(flags.DefaultScaleFactor)
window.AddChild(layout)
window.OnClose(driver.Terminate)
}
func main() {
gl.StartDriver(appMain)
}