[Freeswitch-users] Managed ESL: AccessViolationException

[Ian McMaster]

Hi Grant,

Glad things are starting to work out.
I would say that if you properly protect (by a semaphore, etc) access to
your socket connection to ensure a read is exclusive to one thread you will
be fine.

Maybe it is a better idea in the long run to have a dedicated
connection/socket for a hangup listener?
I have a large event subsystem, and my design is to have a parent thread
listening for all events, and distributing those events (i.e. ESLevent) to
interested listeners (by event type).
In this way there is only one socket connection related to event listening.

Could one connection feed the ESLevents to both your hangup listener (task
1), and your general call processor (task 2)?

Ian.



On Mon, May 19, 2014 at 3:51 AM, Grant Bagdasarian <GB at cm.nl> wrote:

> Hello Ian,
>
>
>
> I ran the code and this was the output, before it threw the exception:
>
> The number is the id of the task.
>
>
>
> 1 - Event-Name: API
>
> 2 - Event-Name: HEARTBEAT
>
> 1 - Event-Name: RE_SCHEDULE
>
> 2 - Event-Name: API
>
> 1 - Event-Name: API
>
> 2 - Event-Name: CHANNEL_OUTGOING
>
> 1 - Event-Name: CHANNEL_STATE
>
> 1 - Event-Name: CHANNEL_ORIGINATE
>
> 1 - Event-Name: CHANNEL_STATE
>
> 1 - Event-Name: CHANNEL_STATE
>
>
>
> When I comment out the Task task2 line there is no error.
>
> As you said, I think this is what exactly happens: ” the second thread
> tries to block on a socket that is already owned by thread 1”
>
>
>
> Just to be sure, the same ESLconnection object can be used by multiple
> threads to receive and send events, as long as the socket reads aren’t done
> by multiple threads at once?
>
>
>
> Thanks
>
>
>
> Grant
>
>
>
> *From:* freeswitch-users-bounces at lists.freeswitch.org [mailto:
> freeswitch-users-bounces at lists.freeswitch.org] *On Behalf Of *Ian McMaster
> *Sent:* Friday, May 16, 2014 4:37 PM
> *To:* FreeSWITCH Users Help
> *Subject:* Re: [Freeswitch-users] Managed ESL: AccessViolationException
>
>
>
> Hi Grant,
>
>
>
> TCP/IP sockets (in general) are designed to be owned by a single thread.
> It is not permitted to block on the same socket by two different threads.
>  I don't know if this is your violation, but it is a problem.
>
> If you want multi-threaded task handlers, the correct socket design is to
> have one thread handling the socket (8021) reads, and sending the event
> read to separate task handlers (in parallel).
>
>
>
> The Receive() method is blocking for an event, and grabbing the first line
> of the event.
>
> Does the error occur when Receive() get's it's first event, or when the
> second thread tries to block on a socket that is already owned by thread 1?
>
> If you comment out "Task task2" does the error still occur?
>
> Ian.
>
>
>
> On Fri, May 16, 2014 at 7:24 AM, Grant Bagdasarian <GB at cm.nl> wrote:
>
> Hello,
>
>
>
> I’m trying to run the following code, but after a few seconds I get
> AccessViolationException:
>
>
>
> class Program {
>
>         static void Main(string[] args) {
>
>
>
>             ESLconnection connection = new ESLconnection("192.168.1.1",
> 8021, "ClueCon");
>
>             connection.SendRecv("event plain ALL");
>
>             Task task1 = Task.Run(() => Receive(1, connection));
>
>             Task task2 = Task.Run(() => Receive(2, connection));
>
>             Console.ReadLine();
>
>         }
>
>
>
>         static void Receive(int id, ESLconnection connection) {
>
>             while (connection.Connected() == 1) {
>
>                 ESLevent eslEvent = connection.RecvEvent();
>
>                 Console.WriteLine("{0} - {1}", id,
> eslEvent.Serialize("").Split(new char[] { '\r', '\n' })[0]);
>
>             }
>
>         }
>
>     }
>
>
>
> What the basic idea behind this is, is to have a Task continuously
> listening for a CHANNEL_HANGUP event, and have the other Task process the
> call in parallel.
>
> Does the exception occur because multiple parallel tasks are trying to
> access the connection object?
>
>
>
> Is the only solution to create a second ESLconnection (HANGUP Handler) and
> register it to receive only calls for a given UUID?
>
>
>
> Regards,
>
>
>
> Grant
>
>
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