Message queue using shared memory/semaphore, how to check if if there is no process connected to the queue?

Question

typedef struct
{
    char data[MESSAGE_SIZE];
} MESSAGE;

typedef struct
{
    sem_t sem_send;
    sem_t sem_receive;
    MESSAGE messages[];
} MQ;

Currently working on message queue, I want to delete the queue but in order to do so I need to destroy the semaphore (sem_destroy ) then shm_unlink but I need to be sure that there is no process currently connected to the queue

How can I achieve this please ?

Answer 1

Maybe what you want is a UNIX socket instead of a message queue. Check man 7 unix , there's an example of how to use it. With UNIX sockets you get:

1. Bidirectional communication (Your code suggests you need that).
2. Connection/Disconnection detection (even in error/abort situations).
3. Packet behaviour with (SOCK_SEQPACKET). Like a message queue.

The message queues don't tell anything about other processes connecting to it. Message queues can exist without any process attach to it.