S01_PLIKI_08

/*
Napisz program, w którym dwa procesy będą zapisywały do jednego pliku, a trzy będą odczytywały. Zastosuj zajmowanie zalecane do synchronizacji pracu procesów.
*/

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/file.h>
#include <fcntl.h>
#include <unistd.h>
#include <wait.h>
#include <string.h>

#define PATHNAME "08_file"
#define BUFFER_SIZE 128
#define NUMBER_OF_WRITERS 2
#define NUMBER_OF_READERS 3
#define MSG_TO_SAVE "Wiadomosc nr "

void error_exit(const char *message)
{
    perror("message");
    exit(EXIT_SUCCESS);
}

void write_to_file(int fd, const char *msg)
{
    if(flock(fd, LOCK_EX) == -1)
        error_exit("flock_ex");

    if(write(fd, msg, strlen(msg)) == -1)
        error_exit("write");
    printf("Zapisano do pliku!\n");

    if(flock(fd, LOCK_UN) == -1)
        error_exit("flock_un");
}

void read_from_file(int fd)
{
    lseek(fd, 0, SEEK_SET);
    ssize_t status;
    char buffer[BUFFER_SIZE];

    if(flock(fd, LOCK_SH) == -1)
        error_exit("flock_sh");

    printf("Odczytano z pliku:\n");
    for(;;) {
        memset(buffer, '\0', BUFFER_SIZE);
        status = read(fd, buffer, BUFFER_SIZE-1);
        if(status == -1)
            error_exit("read");
        else if(status == 0)
            break;
        else
            printf("%s", buffer);
    }

    if(flock(fd, LOCK_UN) == -1)
        error_exit("flock_un");
}

int main(void)
{
    pid_t pids;
    int fd;
    char write_buffer[strlen(MSG_TO_SAVE)+1];

    if((fd = open(PATHNAME, O_RDWR | O_CREAT | O_TRUNC, 0755)) == -1)
        error_exit("open");

    for(int i = 0; i < NUMBER_OF_WRITERS + NUMBER_OF_READERS; i++) {
        pids = fork();
        if(pids == -1)
            error_exit("fork");
        else if(pids == 0){
            printf("Proces nr: %d\n", i+1);
            if(i < NUMBER_OF_WRITERS) {
                sprintf(write_buffer, "%s%d\n", MSG_TO_SAVE, i);
                write_to_file(fd, write_buffer);
            }
            else {
                read_from_file(fd);
            }
            return EXIT_SUCCESS;
        }
    }

    for(int i = 0; i < NUMBER_OF_WRITERS + NUMBER_OF_READERS; i++)
        if(wait(NULL) == -1)
            error_exit("wait");


    return EXIT_SUCCESS;
}