os/signal: Notify for SIGUSR2 from the same proc inside a goroutine doesn't work #12484

willfaught · 2015-09-03T21:24:24Z

A process can't use os/signal.Notify inside a goroutine to signal itself with SIGUSR2.

Works as expected (outside the goroutine):

func main() {
    var c = make(chan os.Signal, 1)
    signal.Notify(c) // outside the goroutine

    var done = make(chan struct{})
    go func() {
        fmt.Println(<-c)
        done <- struct{}{}
    }()
    if err := syscall.Kill(os.Getpid(), syscall.SIGUSR2); err != nil {
        panic(err)
    }
    <-done
}

Doesn't work as expected (inside the goroutine):

func main() {
    var done = make(chan struct{})
    go func() {
        var c = make(chan os.Signal, 1)
        signal.Notify(c) // inside the goroutine

        fmt.Println(<-c)
        done <- struct{}{}
    }()
    if err := syscall.Kill(os.Getpid(), syscall.SIGUSR2); err != nil {
        panic(err)
    }
    <-done
}

Expected: Doesn't hang
Actual: Hangs

The Notify documentation doesn't say it has to be called in the main goroutine.

The text was updated successfully, but these errors were encountered:

stemar94 · 2015-09-03T22:50:34Z

Beware of race conditions...

func main() {
    var done = make(chan struct{})
    var doneReg = make(chan struct{})
    go func() {
        var c = make(chan os.Signal, 1)
        signal.Notify(c) // inside the goroutine
        doneReg <- struct{}{} //signal registration
        fmt.Println(<-c)
        done <- struct{}{}
    }()
    <-doneReg  //wait for registration
    if err := syscall.Kill(os.Getpid(), syscall.SIGUSR2); err != nil {
        panic(err)
    }
    <-done
}

Marvin

willfaught · 2015-09-03T22:58:15Z

Ouch, didn't see it. Thanks!

willfaught closed this as completed Sep 3, 2015

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os/signal: Notify for SIGUSR2 from the same proc inside a goroutine doesn't work #12484

os/signal: Notify for SIGUSR2 from the same proc inside a goroutine doesn't work #12484

willfaught commented Sep 3, 2015

stemar94 commented Sep 3, 2015

willfaught commented Sep 3, 2015

os/signal: Notify for SIGUSR2 from the same proc inside a goroutine doesn't work #12484

os/signal: Notify for SIGUSR2 from the same proc inside a goroutine doesn't work #12484

Comments

willfaught commented Sep 3, 2015

stemar94 commented Sep 3, 2015

willfaught commented Sep 3, 2015