bschofield commented on pull request #663:
URL: https://github.com/apache/pulsar-client-go/pull/663#issuecomment-963949062
@BewareMyPower: I tried this modification of your code, which I think is
exactly the one you suggested:
```go
package main
import (
"fmt"
"sync"
"time"
)
func main() {
m := sync.Mutex{}
c := sync.NewCond(&m)
flag := false
defer m.Unlock()
m.Lock()
go func() {
// No locks here
fmt.Println("Before Broadcast")
flag = true
c.Broadcast()
fmt.Println("After Broadcast")
}()
// Sleep for 2 seconds to make sure c.Broadcast() is called before
c.Wait()
time.Sleep(time.Duration(2) * time.Second)
fmt.Println("Before Wait")
for {
c.Wait()
if flag {
break
}
}
fmt.Printf("After Wait, flag is %v\n", flag)
}
```
When I run that, this happens:
```
Before Broadcast
After Broadcast
Before Wait
fatal error: all goroutines are asleep - deadlock!
goroutine 1 [sync.Cond.Wait]:
sync.runtime_notifyListWait(0xc0000b8050, 0x0)
/home/ben/sdk/go1.17.1/src/runtime/sema.go:513 +0x13d
sync.(*Cond).Wait(0x4b4360)
/home/ben/sdk/go1.17.1/src/sync/cond.go:56 +0x8c
main.main()
/home/ben/tmp/foo.go:29 +0x191
```
So, I think that test case (which you very kindly provided) confirms that we
agree that it really is necessary to call `cond.Broadcast()` after
`cond.Wait()`?
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