S01_PAMIEC_DZIELONA_03

/*
Pokaż rozwi ą zanie problemu czytelników i pisarzy na przyk ł adzie operacji zapisu
i odczytu do pami ę ci dzielonej. Do synchronizacji komunikacji u ż yj semaforów. Do
wypisywania na ekran komunikatów zamiast funkcji printf() u ż yj funkcji write()
*/

#include <stdio.h>
#include <stdlib.h>
#include <sys/ipc.h>
#include <sys/types.h>
#include <sys/shm.h>
#include <sys/sem.h>
#include <unistd.h>
#include <wait.h>
#include <time.h>
#include <string.h>

#define PROCESSES_NUMBER 16
#define BUFFER_SIZE 128

struct shmdata {
    char message[BUFFER_SIZE];
    int readers_number;
};

void error_handler(const char *msg)
{
    perror(msg);
    exit(EXIT_FAILURE);
}

void writer(int id, int mux, int shmid)
{
    struct sembuf up_operation = {0, 1, 0},
              down_operation = {0, -1, 0};
    char info[BUFFER_SIZE];
    struct shmdata *shared_memory;

    if((shared_memory = (struct shmdata *)shmat(shmid, NULL, 0)) == (void *)-1)
        error_handler("shmat_writer");

    if(semop(mux, &down_operation, 1) == -1)
        error_handler("semop_down");

    snprintf(info, BUFFER_SIZE, "Pisarz nr: %d\n", id);
    write(STDOUT_FILENO, info, strlen(info));
    snprintf(shared_memory->message, SHMLBA, "Wiadomosc od pisarza nr %d\n", id);

    if(semop(mux, &up_operation, 1) == -1)
        error_handler("semop_up");

    if(shmdt(shared_memory) == -1)
        error_handler("shmdt");
}

void reader(int id, int mux, int shmid)
{
    struct sembuf message_up_operation = {0, 1, 0},
              message_down_operation = {0, -1, 0},
              readers_up_operation = {1, 1, 0},
              readers_down_operation = {1, -1, 0};
    char info[BUFFER_SIZE];
    struct shmdata *shared_memory;

    if((shared_memory = (struct shmdata *)shmat(shmid, NULL, 0)) == (void *)-1)
        error_handler("shmat_reader");

    if(semop(mux, &readers_down_operation, 1) == -1)
        error_handler("semop_down");
    shared_memory->readers_number++;
    if(shared_memory->readers_number == 1)
        if(semop(mux, &message_down_operation, 1) == -1)
            error_handler("semop_down");
    if(semop(mux, &readers_up_operation, 1) == -1)
        error_handler("semop_up");

    snprintf(info, BUFFER_SIZE, "Czytelnik nr: %d\n", id);
    write(STDOUT_FILENO, info, strlen(info));
    write(STDOUT_FILENO, shared_memory->message, sizeof(shared_memory->message));

    if(semop(mux, &readers_down_operation, 1) == -1)
        error_handler("semop_down");
    shared_memory->readers_number--;
    if(!shared_memory->readers_number)
        if(semop(mux, &message_up_operation, 1) == -1)
            error_handler("semop_up");

    if(semop(mux, &readers_up_operation, 1) == -1)
        error_handler("semop_up");

    if(shmdt(shared_memory) == -1)
        error_handler("shmdt");
}

int main(void)
{
    int mux, shmid;
    pid_t pid;
    int writer_id = 0;
    int reader_id = 0;
    int choice_buffer;

    //////////////////////////

    srand(time((time_t *)NULL));

    if((mux = semget(IPC_PRIVATE, 2, 0775 | IPC_CREAT | IPC_EXCL)) == -1)
        error_handler("semget");

    if((shmid = shmget(IPC_PRIVATE, SHMLBA, 0775 | IPC_CREAT | IPC_EXCL)) == -1)
        error_handler("shmget");

    for(int i = 0; i < 2; i++)
        if(semctl(mux, i, SETVAL, 1) == -1)
            error_handler("semctl_setval");


    for(int i = 0; i < PROCESSES_NUMBER; i++){
        choice_buffer = rand() % 2;
        if(choice_buffer)
            reader_id++;
        else
            writer_id++;

        pid = fork();
        if(pid == -1)
            error_handler("fork");
        else if(pid == 0){
            if(choice_buffer)
                reader(reader_id, mux, shmid);
            else
                writer(writer_id, mux, shmid);
            return EXIT_SUCCESS;
        }
    }

    for(int i = 0; i < PROCESSES_NUMBER; i++)
        if(wait(NULL) == -1)
            error_handler("wait");

    if(shmctl(shmid, IPC_RMID, NULL) == -1)
        error_handler("shmctl");

    if(semctl(mux, 0, IPC_RMID, NULL) == -1)
        error_handler("semctl");

    return EXIT_SUCCESS;
}