The following program returns children that repeat "/ bin / sleep 10". The parent sets up a signal handler for SIGINT, which passes SIGINT to the child. However, sometimes SIGINT is not sent to the child. Why is this and what am I missing?
#include <errno.h> #include <signal.h> #include <stdio.h> #include <stdlib.h> #include <sys/types.h> #include <sys/wait.h> #include <unistd.h> pid_t foreground_pid = 0; void sigint_handler(int sig) { printf("sigint_handler: Sending SIGINT to process %d\n", foreground_pid); if ((foreground_pid != 0) && kill(foreground_pid, SIGCONT) == -1) { perror("sending SIGINT to forground process failed"); printf("foreground_pid == %d", foreground_pid); exit(EXIT_FAILURE); } foreground_pid = 0; } int main(int argc, const char *argv[]) { while (1) { pid_t child_pid; if ((child_pid = fork()) == -1) { perror("fork failed"); exit(EXIT_FAILURE); } if (child_pid) { /* parent */ foreground_pid = child_pid; printf("waiting for child (%d) to complete ...\n", child_pid); fflush(stdout); /* install SIGINT signal handler */ struct sigaction sa; struct sigaction old_handler; sa.sa_handler = sigint_handler; sigemptyset(&sa.sa_mask); sa.sa_flags = SA_RESTART | SA_RESETHAND; sigaction(SIGINT, &sa, NULL); int status = 0; /* wait for child to finish */ if (waitpid(child_pid, &status, 0) == -1) { perror("waitpid failed"); exit(EXIT_FAILURE); } printf(" done.\n"); fflush(stdout); } else { /* child */ char * const argv[] = { "/bin/sleep", "10", NULL}; if (execve(argv[0], argv, NULL) == -1) { perror("execve failed"); exit(EXIT_FAILURE); } exit(EXIT_SUCCESS); } } return EXIT_SUCCESS; } % make && ./foo gcc -Wall -pedantic -std=c99 -D_POSIX_C_SOURCE=200809L foo.c -o foo waiting for child (4582) to complete ... ^Csigint_handler: Sending SIGINT to process 4582 done. waiting for child (4583) to complete ... ^Csigint_handler: Sending SIGINT to process 4583 sending SIGINT to forground process failed: No such process foreground_pid == 4583
source share