[zeromq-dev] ZMQ_MAX_SOCKETS ignored?

Auer, Jens jens.auer at cgi.com
Thu Sep 24 09:16:44 CEST 2015


I am trying to use a context with ZMQ_MAX_SOCKETS to restrict the possible number of connections. In my example, I set ZMQ_MAX_SOCKETS to 2 and start a server with ZMQ_STREAM sockets. The client uses posix sockets to connect to the server. From what I see, it seems that the number of sockets is ignored because I can connect more than 2 clients. Am I missing something?

The server code:
#include <zmq.h>
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main()
    void* ctx = zmq_ctx_new();
    int rc = zmq_ctx_set( ctx, ZMQ_MAX_SOCKETS, 2 );
    assert( rc == 0 );

    int major = 0;
    int minor = 0;
    int patch = 0;

    zmq_version(&major, &minor, &patch);
    printf("This is zeroMQ %d.%d.%d\n", major, minor, patch);

    void* s = zmq_socket(ctx, ZMQ_STREAM);
    rc = zmq_bind(s, "tcp://*:10000");
    assert(rc == 0);

    uint8_t id[256];

        printf("Waiting for client...\n");
        memset(id, 256, '\0');
        int n = zmq_recv(s, id, 256, 0);

        printf("Client connected\n");
        for(int i=0; i != n; ++i)
            printf("%0x", (int)id[i]);
        printf (" (%d)\n", n);

        n = zmq_recv(s, id, 256, 0);
        assert(n == 0);

The client code:
int main()
    struct sockaddr_in serv_addr;
    int sockfd;
    if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
        printf("\n Error : Could not create socket \n");

    memset(&serv_addr, '0', sizeof(serv_addr));

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(10000);

    if(inet_pton(AF_INET, "", &serv_addr.sin_addr)<=0)
        printf("\n inet_pton error occured\n");

    if( connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0)
       printf("\n Error : Connect Failed \n");

    int i; std::cin >> i;

    return 0;

Running the server, and stating four clients gives the following output:
This is zeroMQ 4.1.2
Waiting for client...
Client connected
06b8b4567 (5)
Waiting for client...
Client connected
06b8b4568 (5)
Waiting for client...
Client connected
06b8b4569 (5)
Waiting for client...
Client connected
06b8b456a (5)
Waiting for client...

Since I don't see any disconnect messages for the clients, it looks like all four clients are connected. netstat confirms this.

Best wishes,

Jens Auer | CGI | Software-Engineer
CGI (Germany) GmbH & Co. KG
Rheinstraße 95 | 64295 Darmstadt | Germany
T: +49 6151 36860 154
jens.auer at cgi.com<mailto:jens.auer at cgi.com>
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