If I fork a
child process, and the
child process exits before the parent even calls waitpid, then is the exit status information that is set by waitpid still valid? If so, when does it become not valid; i.e., how do I ensure that I can call waitpid on the
child pid and continue to get valid exit status information after an arbitrary amount of time, and how do I "clean up" (tell the OS that I am no longer interested in the exit status information for the finished
child process)?
I was playing around with the following code, and it appears that the exit status information is valid for at least a few seconds after the
child finishes, but I do not know for how long or how to inform the OS that I won't be calling waitpid again:
#include <assert.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
int main()
{
pid_t pid = fork();
if (pid < 0) {
fprintf(stderr, "Failed to fork\n");
return EXIT_FAILURE;
}
else if (pid == 0) { // code for
child process
_exit(17);
}
else { // code for parent
sleep(3);
int status;
waitpid(pid, &status, 0);
waitpid(pid, &status, 0); // call `waitpid` again just to see if the first call had an effect
assert(WIFEXITED(status));
assert(WEXITSTATUS(status) == 17);
}
return EXIT_SUCCESS;
}
