Sending signal from parent to child process after parent waits in C program

I am attempting to send SIGUSR1 to my child process, child_b, after my parent process waits. However, my handler for sigusr1 is not executing and printing my message "pong quitting" at the end of the output.

#include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <sys/wait.h> #include <signal.h> int fd[2][2]; void sig_handler(int signum) { if (signum == SIGUSR1) { printf("pong quitting\n"); exit(1); } } void f1() { int x = 0; close(fd[0][0]); close(fd[1][1]); while (x <= 100) { printf("ping: %d\n", x); x++; if (write(fd[0][1], &x, sizeof(int)) < 0) { printf("Error writing f1\n"); } if (read(fd[1][0], &x, sizeof(int)) < 0) { printf("Error reading f1\n"); } } close(fd[0][1]); close(fd[1][0]); } void f2() { int x = 0; close(fd[0][1]); close(fd[1][0]); while (x <= 100) { if (read(fd[0][0], &x, sizeof(int)) < 0) { printf("Error reading f2\n"); } if (x <= 100) printf("pong: %d\n", x); x++; if (write(fd[1][1], &x, sizeof(int)) < 0) { printf("Error writing f2\n"); } } close(fd[0][0]); close(fd[1][1]); } int main(void) { for (int i = 0; i < 2; i++) { if (pipe(fd[i]) < 0) { printf("Error opening pipe.\n"); return 1; } } pid_t child_a = fork(); if (child_a < 0) { printf("Error forking child_a.\n"); return 2; } if (child_a == 0) { f1(); } else { pid_t child_b = fork(); if (child_b < 0) { printf("Error forking child_b.\n"); return 3; } if (child_b == 0) { signal(SIGUSR1, sig_handler); f2(); } else { waitpid(child_a, NULL, 0); waitpid(child_b, NULL, 0); kill(child_b, SIGUSR1); } } return 0; } 

I've tried sleeping both the parent and child, as well as rearranging the order of wait and kill; however, I can not get the signal handler to execute. Any help would be appreciated.