Re: [Jack-Devel] Jack session API implementation in jack2

On Fri, Jul 22, 2011 at 11:46:09AM +0200, Stéphane Letz wrote:
> Hi, 
> 
> Looking at Jack session API implementation in jack2 (the goal being to add support for internal server clients also...) I see at least two issues:
> 
> - if a client calls jack_session_notify and a client fails to answer what happens? As far as I understand the code the initial jack_session_notify call will possibly block infinitely in the "while(true)" loop...
> 
> int Read(JackChannelTransaction* trans)
>     {
>         CheckRes(JackResult::Read(trans));
>         while (true) {
>             JackSessionCommand buffer;
> 
>             CheckRes(trans->Read(buffer.fUUID, sizeof(buffer.fUUID)));
>             if (buffer.fUUID[0] == '\0')
>                 break;
> 
>             CheckRes(trans->Read(buffer.fClientName, sizeof(buffer.fClientName)));
>             CheckRes(trans->Read(buffer.fCommand, sizeof(buffer.fCommand)));
>             CheckRes(trans->Read(&(buffer.fFlags), sizeof(buffer.fFlags)));
> 
>             fCommandList.push_back(buffer);
>         }
>         return 0;
>     }

well... a client not calling jack_session_reply and still living, will
hold back the reply.
we might add a timeout for this.
right now, the only solution is killing the offending client.

feel free to propose a better interface for the SM interface. We didnt
declare it stable anyways.

> 
> - if a first client calls jack_session_notify and a second one does jack_session_notify before the first "asynchronous server/clients round trip" is finished, the code here JackEngine.cpp line 942 is called AFAICS: 
> 
>    if (fSessionPendingReplies != 0) {
>         JackSessionNotifyResult res(-1);
>         res.Write(socket);
>         jack_log("JackEngine::SessionNotify ... busy");
>         return;
>     }
> 
> Agin don't this code finally enter the possibly blocking Read given just before?

No it doesnt.

> 
> Comments? How this design can be improved?
> 
> Thanks.
> 
> Stephane 
> 

-- 
torben Hohn

1312554973.27743_0.ltw:2,a <20110805143542.GA23575 at siel dot b>