#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.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))

volatile sig_atomic_t last_signal = 0;
volatile sig_atomic_t sig_count = 0;

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) {
    last_signal = sig;
    sig_count++;
    printf("[%d] received %d SIGUSR1\n", getpid(), sig_count);
}

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 parent_work() {
    struct timespec t = {0, 10*1000000};
    sethandler(SIG_IGN, SIGUSR1);
    for (int i=0; i<100; i++){
        nanosleep(&t,NULL);
        if (kill(0, SIGUSR1)<0)ERR("kill");
    }
    printf("[PARENT] Terminates \n");
}

void child_work(int i) {
    int com=0;
    struct timespec t = {2, 0};
    struct timespec tt;

    /*for (int i=0; i<100; i++){
        sigsuspend(&oldmask);
        com++;
        printf("[%d] received %d SIGUSR2\n", getpid(), com);

    }*/
    //sethandler(sig_handler,SIGUSR1);
    sleep(1);
    int out;
    ssize_t count;
    srand(time(NULL)*getpid());
    int s=10+rand()%(100-10+1);
    printf("n=%d, s=%d\n", i, s);


    char *buf=malloc(s*1024);
    if(!buf) ERR("malloc");
    memset(buf, i+'0', s*1024);
    char name[15];
    sprintf(name, "%d.TXT", getpid());
    //printf("%s", name);
    if((out=TEMP_FAILURE_RETRY(open(name,O_WRONLY|O_CREAT|O_TRUNC|O_APPEND,0777)))<0)ERR("open");
    while(0!=nanosleep(&t,NULL))
    {
        while(0<sig_count-com)
        {
            if((count=bulk_write(out,buf,s))<0) ERR("write");
            com++;
        }
    }
    if(TEMP_FAILURE_RETRY(close(out)))ERR("close");
    //printf("[%d] received %d SIGUSR1\n", getpid(), com);
}

void create_children(int n, char** arg) {
    pid_t s;
    for (int i=1;i<n;i++) {
        if((s=fork())<0) ERR("Fork:");
        if(!s) {
            sethandler(sig_handler,SIGUSR1);
            child_work(atoi(arg[i]));
            exit(EXIT_SUCCESS);
        }
    }
}


void usage(char *name){
    fprintf(stderr,"USAGE: %s 0<n\n",name);
    exit(EXIT_FAILURE);
}

int main(int argc, char** argv) {
    int n=argc-1;
    if(argc<2)  usage(argv[0]);

    //sethandler(sig_handler,SIGUSR1);

    create_children(argc, argv);
    parent_work();
    while(n>0){
        sleep(3);
        pid_t pid;
        for(;;){
            pid=waitpid(0, NULL, WNOHANG);
            if(pid>0) n--;
            if(0==pid) break;
            if(0>=pid) {
                if(ECHILD==errno) break;
                ERR("waitpid:");
            }
        }
        printf("PARENT: %d processes remain\n",n);
    }
    return EXIT_SUCCESS;
}