mq_open() - too many open files

Question

I'm trying to write a client and server which are going to exchange data by using POSIX message queue. I tried to do it by looking at the examples I saw in the Internet and the documents of the course. But, I am stuck in. When I run it, I get "Too many open files" error. Here is my code:

Client:

int main( int argc, char *argv[]) {

    //Open its queue, which is client queue
    char cq_name[10];
    sprintf( cq_name, "/cq%i", getpid());
    printf( "Client Queue name: %s\n", cq_name);

    mqd_t cq_id = mq_open( cq_name, O_CREAT | O_RDWR, 0666, NULL);
    if( cq_id == -1) {

            printf( "Error in cq: %s\n", strerror( errno));
            return -1;
    }

    printf( "Name: %s\n", argv[1]);

    //Connect to the server message queue
    mqd_t sq_id = mq_open( argv[1], O_RDWR);

    if( sq_id == -1) {

            printf( "Error in sq: %s\n", strerror( errno));
            return -1;
    }

...

Server:

int main( int argc, char *argv[]) {

    //The server message queue
    struct mq_attr attr;
    attr.mq_flags = 0;
    attr.mq_curmsgs = 0;

    printf( "Name: %s\n", argv[1]);

    mqd_t id = mq_open( argv[1], O_CREAT | O_RDWR, 0666, NULL);

    //Check the message queue
    if( id == -1) {

            printf( "Error: %s\n", strerror(errno));
    }

    printf( "Check Point 1 - %i\n", id);

...

Can you help me to figure out what the problem is. Thanks in advance..

Answer 1

I hit this problem this week - that I could only open a max of 10 mqs.

My intent is to use mqs to pass notification of events to threads. In my case an event_id is just an int. By using specifying non-default attributes in the call to mq_open like so:

char mq_name[128];
sprintf(mq_name, "%s.%d", MQ_NAME, nnid);

struct mq_attr attrib;
attrib.mq_flags = 0;
attrib.mq_maxmsg = 4;
attrib.mq_msgsize = sizeof(int);
attrib.mq_curmsgs = 0;

retval = mq = mq_open(mq_name, O_RDWR | O_CREAT | O_EXCL, 0644, &attrib);

I am now able to open up to 256 mqs before mq_open() fails.