c - Shared Memory and semaphores for (multiple) client and server game -


i have program little game course in c , has done using shared-memory, semaphores , client/server architecture can handle multiple clients (the exact requirement game 2).

the 2 clients need turns in turns , represented same program (no fork() involved here - both started ./client)

the server has create resources when starts up. main problem regarding semaphores. (the shared memory , game-logic stuff works or isn't difficult implement.)

to decide if server or client has access shared-memory need 1 semaphore. need second 1 decide of clients has access. right?

so got hint done assigning ids clients. shared-memory has 3 additional variables so:

struct game {     int id_needed, client_id, id_ready;     ... // additional stuff needed game logic };

as server boots i'm initializing 1 semaphore 0 , other 1 1. when first client appears checks if id still 0 (it's initialized zero)

if so, tries this:

while(my_id == 0) {    if(semaphore_down(semaphore_1) == 0) // check if have access shared mem    {        shared_memory->id_needed = 1;        if(shared_memory->id_ready == 1)        {            my_id = shared_memory->client_id;            (void) printf("debugging: id %d\n", my_id);        }    } } shared_memory->id_needed = 0;

and in server ...

while(1) {     if(shared_memory->id_needed = 1)     {         (void) printf("debugging: id needed client!");         shared_memory->client_id++;         shared_memory->id_ready = 1;         (void) printf("debbuging: dispatched new id: %d", shared_memory->client_id);     }     // if enough players, start game ... }

i'm stuck here. server increments id (which logical), i'm stuck resolve problem.

i want clients work alternately on shared-memory , server check values of game etc.

i've never worked semaphores before , documentation or examples find work 1 client , 1 server, never multiple clients.

please enlighten me!

i see 1 strange thing , 2 things mistakes here

  1. i see semaphore_down no semaphore_up in code showed
  2. you assign instead of comparing: if(shared_memory->id_needed = 1)
  3. even if comparison, not right anyway since compiler free optimize out. make variable volatile hint compiler variable can change outside of serial code flow. or better declare atomic.

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