Because the wait on the condition is in another Go routine, so the the
Broadcast occurs before all of the routines are waiting. Broadcast only wakes
up currently waiting routines.
> On Jul 18, 2024, at 9:01 AM, Lammie Jonson <jrubia...@gmail.com> wrote:
>
> // I am not sure why this code sometimes deadlocks, but sometimes it doesn't.
> // Hopefully someone will have some suggestions
>
> package main
>
> // ??? sometimes deadlocks
>
> import (
> "fmt"
> "sync"
> "time"
> )
>
> type Button struct {
> Clicked *sync.Cond
> }
>
> func main() {
> button := Button{
> Clicked: sync.NewCond(&sync.Mutex{}),
> }
>
> // running on goroutine every function that passed/registered
> // and wait, not exit until that goroutine is confirmed to be running
> subscribe := func(c *sync.Cond, param string, fn func(s string)) {
> var goroutineRunning sync.WaitGroup
> var cnt = 0
> cnt = cnt + 1
>
> fmt.Println("cnt:", cnt)
> goroutineRunning.Add(1)
>
> go func(p string) {
> goroutineRunning.Done()
> c.L.Lock() // critical section
> defer c.L.Unlock()
>
> fmt.Println("Registered and wait ... ")
> // HANG SPOT: can hang here
> c.Wait()
> fmt.Println("afer goroutine wait for:", param)
>
> fn(p)
> }(param)
> fmt.Println("call wait before goroutine exit")
> goroutineRunning.Wait()
> fmt.Println("after wait, subscribe exits")
> }
>
> var clickRegistered sync.WaitGroup
>
> for _, v := range []string{
> "Maximizing window.",
> "Displaying annoying dialog box!",
> "Mouse clicked."} {
>
> clickRegistered.Add(1)
>
> subscribe(button.Clicked, v, func(s string) {
> fmt.Println(s, "****************************")
> clickRegistered.Done()
> })
> }
>
> fmt.Println("broadcast")
> // is supposed to get the goroutines past HANG SPOT
> button.Clicked.Broadcast()
> time.Sleep(4000 * time.Millisecond)
>
> clickRegistered.Wait()
> }
>
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