Programming

In my server code there is a thread per client...
The server call accept() and after that start the thread.
So there is a thread for client that save in RAM the client's message, that will be send to other clients.
Now in RAM I have created a shared memory in which thread read and write(save) client's message :

server.c

Code:

Code:

socket()
bind()
..
...
...int shmid;
    key_t key;
    char *shm, *s;

    key = 5678;

    if ((shmid = shmget(key, 10000, IPC_CREAT | 0666)) < 0) {
        perror("shmget");
        exit(1);
    }

    if ((shm = shmat(shmid, NULL, 0)) == (char *) -1) {
        perror("shmat");
        exit(1);
    }
   int *mem=mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, shmid, 0);
     ftruncate(shmid, 4096); 

while(1){
...
...
...
}

Now I must synchronized the threads by semaphore to read and write into shared memory.Like this : all thread can read, but when a thread write other thread can't do anything , only WAIT that the writing thread signals it has finished. I don't know how can I do... Can someone help me with some example? how can I manage a semaphore??
Thank you very much!

If all processing is done by multiple threads in a single process, you can use a pthread_rwlock that's visible to all your threads.

Yes there is the main in which server accept a client and then call the thread to manage the client's request! It 's done for all clients that connects to the server! First the server accepts and then call the thread! Thank you very much... now I'll study the working of pthread_rwlock!