8 (по счету)

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

int K0[2];
int K1[2];

int interrupt = 0;

void my_pause(){
        while(!interrupt){}
}

void hdl(int sig){
        if(sig == SIGUSR1){
                interrupt = 1;
        }
}

int main(){
        signal(SIGUSR1, hdl);

        pid_t P1;

        pipe(K0);
        pipe(K1);

        P1 = fork();

        if (P1 == 0){
                printf("        Start P1\n");

                pid_t P3;
                P3 = fork();


                if (P3 == 0){
                        printf("                        Start P3\n");

                        close(K1[0]);

                        pid_t iam = getpid();
                        char text[] = "First message from P3 to parent thread !"; //сообщение
                        char message[44];
                        sprintf(message,"%d%s",iam,text);

                        write(K1[1],message,44);
                        printf("                        Send data from P3 to Р0\n");

                        kill(getppid(),SIGUSR1);
                        printf("                        Send signal from P3 to P1\n");

                        my_pause();
                        printf("                        Get signal from P2\n");

                        //close(K1[0]);
                        char text1[] = "Second message from P3 to parent thread!";
                        sprintf(message,"%d%s",iam,text1);

                        write(K1[1],message,44);
                        printf("                        Send data from P3 to Р0\n");

                        printf("                        End P3\n");
                        exit(0);
                }
                else{
                        close(K1[0]);
                        close(K0[0]);

                        my_pause();
                        printf("        Get signal from P3\n");

                        pid_t iam = getpid();
                        char text[] = "Message from P1 thread to parent thread!";
                        char message[44];
                        sprintf(message,"%d%s",iam,text);

                        write(K1[1],message,44);
                        printf("        Send data from P1 to P0\n");

                        char pid[4];
                        sprintf(pid,"%d",P3);

                        write(K0[1],pid,4);
                        printf("        Send pid P3 to P2 by K0\n");

                        int signal;
                        waitpid(P3,&signal,0);
                        printf("        Waited for end of P3\n");

                        printf("        End P1\n");
                        exit(0);
                }
        }
        else{

                pid_t P2;

                P2 = fork();

                if (P2 == 0){
                        close(K1[0]);
                        close(K0[1]);

                        int pid;
                        char pid_s[4];
                        printf("                Start P2\n");
                        printf("                Wait for data from K0\n");
                        read(K0[0],pid_s,4);
                        pid = atoi(pid_s);
                        printf("                Get a pid of P3 from P1 by K0\n");

                        pid_t iam = getpid();
                        char text[] = "Message from P2 thread to parent thread!";
                        char message[44];
                        sprintf(message,"%d%s",iam,text);

                        write(K1[1],message,44);
                        printf("                Send data from P2 to P0\n");

                        kill(pid,SIGUSR1);
                        printf("                Send signal from P2 to P3\n");

                        printf("                End P2\n");
                        exit(0);

                }
                else{
                        close(K1[1]);

                        int status;
                        waitpid(P1,&status,0);

                        printf("Waited for end of child thread\n");

                        char messages[44];

                        printf("All messages from child thread:\n");
                        read(K1[0],messages,44);
                        write(1,messages,44);
                        printf("\n");

                        read(K1[0],messages,44);
                        write(1,messages,44);
                        printf("\n");

                        read(K1[0],messages,44);
                        write(1,messages,44);
                        printf("\n");

                        read(K1[0],messages,44);
                        write(1,messages,44);
                        printf("\n");
                }
        }
        return 0;
}