#define _GNU_SOURCE
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <sys/time.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <string.h>
#include <time.h>
#define ERR(source) (fprintf(stderr,"%s:%d\n",__FILE__,__LINE__),\
                     perror(source),kill(0,SIGKILL),\
                                     exit(EXIT_FAILURE))

int sig_count = 0, sig_alarm = 0;

ssize_t bulk_write(int fd, char *buf, size_t count){
        ssize_t c;
        ssize_t len=0;
        do{
                c=TEMP_FAILURE_RETRY(write(fd,buf,count));
                if(c<0) return c;
                buf+=c;
                len+=c;
                count-=c;
        }while(count>0);
        return len ;
}

void sethandler( void (*f)(int), int sigNo) {
    struct sigaction act;
    memset(&act, 0, sizeof(struct sigaction));
    act.sa_handler = f;
    if (-1==sigaction(sigNo, &act, NULL)) ERR("sigaction");
}

void sig_handler(int sig) {
    sig_count++;
}

void alarm_handler(int sig) {
    sig_alarm = 1;
}

void child_work(int n) {
    pid_t pid = getpid();
    srand(pid);

    char name[8];
    sprintf(name, "%d", pid);
    strcat(name, ".txt");

    int out;
    ssize_t s = 1024*(rand()%91+10);
    char *buf = malloc(s);
    if(!buf) ERR("malloc");
    for(int i=0;i<s;i++)
        buf[i]=n+48;
    if((out=TEMP_FAILURE_RETRY(open(name,O_WRONLY|O_CREAT|O_TRUNC|O_APPEND,0777)))<0) ERR("open");

    sethandler(sig_handler, SIGUSR1);
    sethandler(alarm_handler,SIGALRM);

    alarm(1);
    while(!sig_alarm)
        while(sig_count>0)
        {
            if((s=bulk_write(out,buf,s))<0) ERR("write");
            sig_count--;
        }

    if(TEMP_FAILURE_RETRY(close(out))) ERR("close");
    free(buf);
}

void parent_work() {
    struct timespec t = {0, 10*1000000};
    sethandler(SIG_IGN,SIGUSR1);
    sethandler(alarm_handler,SIGALRM);

    alarm(1);
    while(!sig_alarm){
        nanosleep(&t,NULL);
        if(kill(0,SIGUSR1))ERR("kill");
    }
}

void usage(char *name){
    fprintf(stderr,"USAGE: %s n1 n2 n3 ... \n",name);
    fprintf(stderr,"n1, n2, n3, ... - number [0-9]\n");
    exit(EXIT_FAILURE);
}

int main(int argc, char** argv) {
    int n;
    pid_t pid;
    for(int i=1; i<argc; i++)
    {
        n = atoi(argv[i]);
        if(n<0 || n>9) usage(argv[0]);
        if((pid=fork())<0) ERR("fork");
        if(0==pid)
        {
            child_work(n);
            return EXIT_SUCCESS;
        }
    }
    parent_work();
    while(wait(NULL)>0);
    return EXIT_SUCCESS;
}