panic when Disconnect() invoked after internalConnLost

[jpwsutton]

migrated from Bugzilla #464559
status RESOLVED severity normal in component MQTT-Go for 1.1
Reported in version 0.9 on platform PC
Assigned to: Al Stockdill-Mander

On 2015-04-14 00:22:00 -0400, shirou WAKAYAMA wrote:

paho library causes panic when invoke Disconnect().

Here is my sample program.

package main

import (
"fmt"
"time"

MQTT "git.eclipse.org/gitroot/paho/org.eclipse.paho.mqtt.golang.git"
)

func main() {
opts := MQTT.NewClientOptions().AddBroker("tcp://localhost:1883")
opts.SetCleanSession(true)

c := MQTT.NewClient(opts)
if token := c.Connect(); token.Wait() && token.Error() != nil {
panic(token.Error())
}
fmt.Println("plz down mosquitto now")
time.Sleep(5 * time.Second)

c.Disconnect(200)
time.Sleep(5 * time.Second)

}

How to reproduce:

1. mosquitto up
2. go run close_panic.go
3. mosquitto down after "plz down mosquitto now" shows
4. wait 5 sec
5. panic

This is caused by close(c.stop) in the Client.disconnect(). c.stop is already closed at the internalConnLost(), so the second disconnect() close already closed channel.

To avoid panic, I think check the channel is already close or not using select/case.

@@ -382,7 +383,12 @@ func (c *Client) internalConnLost(err error) {
}

func (c *Client) disconnect() {

•   close(c.stop)
  

•   select {
  

•   case _, ok := <-c.stop:
  

•           if ok {
  

•                   close(c.stop)
  

•           }
  

•   }
  

It can fix problem at least my environment.

Thank you.

On 2015-04-14 00:42:15 -0400, shirou WAKAYAMA wrote:

I forget to add error and my environment.

go version go1.4.2 darwin/amd64

panic: close of closed channel

goroutine 1 [running]:
git.eclipse.org/gitroot/paho/org%2eeclipse%2epaho%2emqtt%2egolang%2egit.(_Client).disconnect(0xc20805e000)
/Users/blah/src/git.eclipse.org/gitroot/paho/org.eclipse.paho.mqtt.golang.git/client.go:385 +0x3a
git.eclipse.org/gitroot/paho/org%2eeclipse%2epaho%2emqtt%2egolang%2egit.(_Client).Disconnect(0xc20805e000, 0xc8)
/Users/blah/src/git.eclipse.org/gitroot/paho/org.eclipse.paho.mqtt.golang.git/client.go:355 +0x466
main.main()
/Users/blah/src/git.eclipse.org/gitroot/paho/org.eclipse.paho.mqtt.golang.git/samples/close_panic.go:21 +0x210

goroutine 17 [syscall, locked to thread]:
runtime.goexit()
/usr/local/Cellar/go/1.4.2/libexec/src/runtime/asm_amd64.s:2232 +0x1

goroutine 6 [select]:
git.eclipse.org/gitroot/paho/org%2eeclipse%2epaho%2emqtt%2egolang%2egit.func·003()
/Users/blah/src/git.eclipse.org/gitroot/paho/org.eclipse.paho.mqtt.golang.git/router.go:131 +0x4e6
created by git.eclipse.org/gitroot/paho/org%2eeclipse%2epaho%2emqtt%2egolang%2egit.(*router).matchAndDispatch
/Users/blah/src/git.eclipse.org/gitroot/paho/org.eclipse.paho.mqtt.golang.git/router.go:161 +0x166

goroutine 13 [sleep]:
git.eclipse.org/gitroot/paho/org%2eeclipse%2epaho%2emqtt%2egolang%2egit.(_Client).reconnect(0xc20805e000)
/Users/blah/src/git.eclipse.org/gitroot/paho/org.eclipse.paho.mqtt.golang.git/client.go:287 +0xd83
created by git.eclipse.org/gitroot/paho/org%2eeclipse%2epaho%2emqtt%2egolang%2egit.(_Client).internalConnLost
/Users/blah/src/git.eclipse.org/gitroot/paho/org.eclipse.paho.mqtt.golang.git/client.go:377 +0xe5

exit status 2

Thank you.

On 2015-04-17 11:19:32 -0400, Al Stockdill-Mander wrote:

http://git.eclipse.org/c/paho/org.eclipse.paho.mqtt.golang.git/commit/?id=SHA: 15034ff

Thanks

[dh1tw]

I can confirm that this bug still exists in the latest master version (#44eec14).