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// this example taken from
// https://gist.github.com/sebcat/a61b2ed859cee16c560e
// FreeBSD has pdfork which uses file descriptors instead of PIDs for
// managing processes. This allows for race-less process supervision and
// for using the traditional multiplexing calls (e.g., select). There's no
// need wait()ing for SIGCHLD, &c.
//
// This example forks a child that sleeps for a certain time while the
// parent is waiting for the child to exit, or for a timeout to be reached,
// whichever comes first. The time values (in seconds) are provided from argv
//
// % ./pdfork
// usage: pdfork <child-sleep> <parent-wait>
// % ./pdfork 2 10
// child: exit
// parent: child exited
// % ./pdfork 10 2
// parent: kill
#include <sys/types.h>
#include <sys/select.h>
#include <sys/procdesc.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#define DURATION_MAX 100
static long time_or_die(const char *str, const char *name) {
char *cptr;
long res;
res = strtol(str, &cptr, 10);
if (errno == ERANGE || *cptr != '\0') {
fprintf(stderr, "invalid %s parameter\n", name);
exit(EXIT_FAILURE);
} else if (res < 0 || res > DURATION_MAX) {
fprintf(stderr, "%s out of permitted range\n", name);
exit(EXIT_FAILURE);
}
return res;
}
int main(int argc, char *argv[]) {
struct timeval to={0,0};
long child_sleep, parent_wait;
int fd, ret;
fd_set fds;
if (argc != 3) {
fprintf(stderr, "usage: pdfork <child-sleep> <parent-wait>\n");
return EXIT_FAILURE;
}
child_sleep = time_or_die(argv[1], "child-sleep");
parent_wait = time_or_die(argv[2], "parent-wait");
if ((ret = pdfork(&fd, 0)) == -1) {
perror("pdfork");
return EXIT_FAILURE;
} else if (ret == 0) {
sleep((unsigned int)child_sleep);
fprintf(stderr, "child: exit\n");
exit(0);
} else {
FD_ZERO(&fds);
FD_SET(fd, &fds);
to.tv_sec = parent_wait;
if ((ret = select(fd+1, &fds, NULL, NULL, &to)) == -1) {
perror("select");
return EXIT_FAILURE;
} else if (ret == 0) {
fprintf(stderr, "parent: kill fd %d\n", fd);
pid_t pid;
pdgetpid(fd, &pid);
pdkill(fd, 9);
} else {
fprintf(stderr, "parent: child exited\n");
}
}
// and generate a couple of errors for valgrind
int *badfd = malloc(sizeof(int));
free(badfd);
if (pdfork(badfd, 0) > 0)
{
fprintf(stderr, "parent after 1st bad pdfork\n");
int anotherfd;
int badflag;
pid_t* pbadpid = malloc(sizeof(pid_t));
free(pbadpid);
pdgetpid(anotherfd, pbadpid);
pdfork(&anotherfd, badflag);
}
return EXIT_SUCCESS;
}
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