为什么从代码调用Setenv不起作用？

Question

I have a simple test project which is expected to print goroutine scheduling messages while it is running.

Setting the env from Goland configuration it works. but it doesn't from code like below, the app doesn't print scheduling infomation. Anybody explains what happens ehre?

func TestScheduler1() {

    var wg sync.WaitGroup
    wg.Add(10)

    for i := 0; i < 10; i++ {
        go work(&wg)
    }

    wg.Wait()
    // Wait to see the global run queue deplete.
    time.Sleep(3 * time.Second)
}

func work(wg *sync.WaitGroup) {
    time.Sleep(time.Second)

    var counter int
    for i := 0; i < 1e10; i++ {
        counter++
    }

    wg.Done()
}

init function is like:

 func init()  {
    os.Setenv("GOMAXPROCS", "1")
    os.Setenv("GODEBUG", os.Getenv("GODEBUG") + "schedtrace=1000,scheddetail=1")
}

Answer 1

go command documentation mentions that go examines some environment variables:

The go command, and the tools it invokes, examine a few different environment variables.

So, env variables are checked before the program starts, i.e in build time. When you set these variables from code, the program already runs.

It works from the IDE since the variables are applied before the compilation, therefore the code runs with all the changes you need.