SPO-2-NIX

#include <ncurses.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <string.h>
#include <sys/wait.h>

#define MAX_PROCESS_NUMBER 100

void printString();
void make_string(int num);
void quit(int sig);
void chgFlag(int);

struct sigaction  endProcessSignal, printingSignal;
int num = 0;
char string[MAX_PROCESS_NUMBER][200];
int allowPrint = 1, killflag=0;
int parentPid;

void bindSignals()
{
    endProcessSignal.sa_handler = quit;
    sigaction(SIGUSR1,&endProcessSignal,NULL);
    printingSignal.sa_handler = chgFlag;
    sigaction(SIGUSR2,&printingSignal,NULL);
}

void init()
{
    initscr();
    curs_set(0);
    refresh();
    bindSignals();
}

void child()
{
    allowPrint;
    int pos; // extract pos changing to separate func ?
    pos = getpid();
    make_string(num);
    pos -= parentPid; // position in list ?
    if(pos > num){
        pos = num;
    }
    while(!killflag)
    {
        if(allowPrint)
        {
            printString();
            allowPrint = 0;
            kill(getppid(), SIGUSR2); // send sigusr2 to parent ?
        }
    }
}

int waitForChild(pid_t childPid)
{
    pid_t w;
    int status;
    do
    {
        w = waitpid(childPid, &status, WUNTRACED | WCONTINUED);
    }while(!WIFEXITED(status) && !WIFSIGNALED(status));
    return status;
}

void onQuit(pid_t* pidArray)
{
    for(int i = 0; i < num; i++ )
    {
        kill(pidArray[i], SIGUSR1);
        waitForChild(pidArray[i]);
    }
    clear();
    endwin();
}

int main()
{
    init();
    pid_t childPids[MAX_PROCESS_NUMBER], tpid;
    int currentProcessIndex = 0;
    char s;
    while(1)
    {
        fflush(stdin);
        s = getchar();

        switch(s)
        {
        case 'q':
            onQuit(childPids);
            exit(EXIT_SUCCESS);
            break;

        case '+':

            tpid = fork();

            switch(tpid)
            {
            case 0:
                child();
                exit(EXIT_SUCCESS);
                break;

            case -1:
                printw("Error!\n");
                break;

            default:
                //  In parent process
                allowPrint = num ? allowPrint : 1;
                ++num;
                childPids[num-1] = tpid;
                usleep(10); // wait for sigaction binding in child process
                break;
            }
            break;
        case '-':
            if( num )
            {
                kill(childPids[num-1], SIGUSR1);
                waitForChild(childPids[num-1]);
                --num;
            }
            break;
        default:
            break;
        }

        if( allowPrint && num)
        {
            currentProcessIndex = currentProcessIndex >= num ? 0 : currentProcessIndex;
            kill(childPids[currentProcessIndex], SIGUSR2);
            allowPrint = 0;
            currentProcessIndex++;
        }
    }
    clear();
    endwin();
    exit(EXIT_SUCCESS);
}

void printString()
{

    int pos = getpid();
    char c = 13;

    pos -= parentPid;
    if(pos > num){
        pos = num;
    }

    for(int i = 0; i < strlen(string[pos]); i++)
    {
        printw("%c", string[pos][i]);
        refresh();
        usleep(100000);
    }
}

void make_string(int num)
{
    int pos=getpid()-parentPid;
    int m=getpid();

    if(pos>num)
        pos=num;
    char c =  '0' + num;
    for (int i = 0; i < 10; ++i)
    {
        string[pos][i] = c;
    }
}

void quit(int sig)
{
    killflag = 1;
}

void chgFlag(int a)
{
    allowPrint = 1;
}