Re: SUBSCRIBE TO A CHANNEL USING C LANGUAGE.

[Salvatore Sanfilippo]

You can check how I do it in the "sentinel.c" code in the Redis
distribution, but I agree that this should be more clearly documented.

In short, to subscribe to "ILOVEUPPERCASE" channel:

void myCallBackFunction(redisAsyncContext *c, void *reply, void *privdata) {
redisReply *r;
if (r == NULL) return;

/* Sanity check in the reply we expect, so that the code that follows
* can avoid to check for details. */
if (r->type != REDIS_REPLY_ARRAY ||
r->elements != 3 ||
r->element[0]->type != REDIS_REPLY_STRING ||
r->element[1]->type != REDIS_REPLY_STRING ||
r->element[2]->type != REDIS_REPLY_STRING ||
strcmp(r->element[0]->str,"message") != 0) return;

printf("%s\n",r->element[2]->str);
}

retval = redisAsyncCommand(context, myCallBackFunction, NULL,
"SUBSCRIBE %s", "ILOVEUPPERCASE");


Cheers,
Salvatore

On Wed, Nov 28, 2012 at 10:30 AM, MSP <mohitb...@gmail.com> wrote:
> I want to listen for messages continuously on a channel (PUB/SUB Redis)
> using C launguage . I am using hiredis library.
> Can anyone suggest the way to achieve this?
>
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--
Salvatore 'antirez' Sanfilippo
open source developer - VMware
http://invece.org

Beauty is more important in computing than anywhere else in technology
because software is so complicated. Beauty is the ultimate defence
against complexity.
— David Gelernter

[MSP]

Thank you so much...done with my problem statement now.

But one more thing.....

I have written a client in c that listen on particular channel say "CHNL101" and i have a publisher written in c which publishes the message to the same channel.

In this scenario client successfully receives the messages.

But when i am publishing through redis-cli....client does not recieve anything. WHY???

i am publishing like this

redis 127.0.0.1:6379> publish chnl mohit

(integer) 0

[Salvatore Sanfilippo]

On Thu, Nov 29, 2012 at 10:30 AM, MSP <mohitb...@gmail.com> wrote:
> redis 127.0.0.1:6379> publish chnl mohit
> (integer) 0

The hint is in the "(integer) 0".

There are no subscribers for that channel according to Redis.

Cheers,
Salvatore

[MSP]

Got it....CHNL and chnl are different channels.

So channel names are case-sensitive unlike redis commands...

[Salvatore Sanfilippo]

On Thu, Nov 29, 2012 at 10:38 AM, MSP <mohitb...@gmail.com> wrote:
> So channel names are case-sensitive unlike redis commands...

Case sensitive as key names indeed.

[MSP]

Hi,

According to hiredis documentation : "When redisAsyncCommand  function is called, the connection is not immediately terminated. Instead, new commands are no longer accepted and the connection is only terminated when all pending commands have been written to the socket, their respective replies have been read and their respective

callbacks have been executed."

Core is generated by following piece of code....

for(i=0;i<5000;i++)

        redisAsyncCommand(c, getCallback, NULL, "get num");

    redisAsyncDisconnect(c);

publisher: async.c:289: __redisAsyncDisconnect: Assertion `__redisShiftCallback(&ac->replies,((void *)0)) == -1' failed.

Aborted (core dumped)

For values of i upto 500 ,this code  is working fine

[MSP]

Hi...

retval = redisAsyncCommand(context, myCallBackFunction, NULL, 

"SUBSCRIBE %s", "ILOVEUPPERCASE");  

After this my program starts listening on the channel for messages infinitely.....

can you suggest how to return from this call ? 

This piece of code is NOT behaving correctly

    redisAsyncCommand(c,myCallback, NULL, "SUBSCRIBE CHNL");

    redisAsyncDisconnect(c);

i mean redisAsyncDisconnect(c) will wait for the callback to return....

 

Plz throw some light on how to return from subscribe command.