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Double-fork() to avoid zombies

This commit is contained in:
Axel Wagner 2010-11-10 18:46:47 +01:00
parent 23b62f621d
commit eada483765
1 changed files with 39 additions and 12 deletions
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51
i3bar/src/child.c
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@ -12,6 +12,7 @@
#include <unistd.h> #include <unistd.h>
#include <sys/types.h> #include <sys/types.h>
#include <signal.h> #include <signal.h>
#include <sys/wait.h>
#include <stdio.h> #include <stdio.h>
#include <fcntl.h> #include <fcntl.h>
#include <string.h> #include <string.h>
@ -100,41 +101,67 @@ void child_sig_cb(struct ev_loop *loop, ev_child *watcher, int revents) {
/* /*
* Start a child-process with the specified command and reroute stdin. * Start a child-process with the specified command and reroute stdin.
* We actually start a $SHELL to execute the command so we don't have to care * We actually start a $SHELL to execute the command so we don't have to care
* about arguments and such * about arguments and such.
* We also double-fork() to avoid zombies and pass the pid of the child through a
* temporary pipe back to i3bar
* *
*/ */
void start_child(char *command) { void start_child(char *command) {
child_pid = 0; child_pid = 0;
if (command != NULL) { if (command != NULL) {
int fd[2]; int fd[2], tmp[2];
/* This pipe will be used to communicate between e.g. i3status and i3bar */
pipe(fd); pipe(fd);
child_pid = fork(); /* We also need this temporary pipe to get back the pid of i3status */
switch (child_pid) { pipe(tmp);
switch (fork()) {
case -1: case -1:
ELOG("Couldn't fork()\n"); ELOG("Couldn't fork()\n");
exit(EXIT_FAILURE); exit(EXIT_FAILURE);
case 0: case 0:
/* Child-process. Reroute stdout and start shell */ /* Double-fork(), so the child gets reparented to init */
close(fd[0]); switch(child_pid = fork()) {
case -1:
ELOG("Couldn't fork() twice\n");
exit(EXIT_FAILURE);
case 0:
/* Child-process. Reroute stdout and start shell */
close(fd[0]);
dup2(fd[1], STDOUT_FILENO); dup2(fd[1], STDOUT_FILENO);
static const char *shell = NULL; static const char *shell = NULL;
if ((shell = getenv("SHELL")) == NULL) if ((shell = getenv("SHELL")) == NULL)
shell = "/bin/sh"; shell = "/bin/sh";
execl(shell, shell, "-c", command, (char*) NULL); execl(shell, shell, "-c", command, (char*) NULL);
return; return;
default:
/* Temporary parent. We tell i3bar about the pid of i3status and exit */
write(tmp[1], &child_pid, sizeof(int));
close(tmp[0]);
close(tmp[1]);
exit(EXIT_SUCCESS);
}
default: default:
/* Parent-process. Rerout stdin */ /* Parent-process. Rerout stdin */
close(fd[1]); close(fd[1]);
dup2(fd[0], STDIN_FILENO); dup2(fd[0], STDIN_FILENO);
/* We also need to get the pid of i3status from the temporary pipe */
size_t rec = 0;
while (rec < sizeof(int)) {
rec += read(tmp[0], &child_pid, sizeof(int) - rec);
}
/* The temporary pipe is no longer needed */
close(tmp[0]);
close(tmp[1]);
break; break;
} }
} }
wait(0);
/* We set O_NONBLOCK because blocking is evil in event-driven software */ /* We set O_NONBLOCK because blocking is evil in event-driven software */
fcntl(STDIN_FILENO, F_SETFL, O_NONBLOCK); fcntl(STDIN_FILENO, F_SETFL, O_NONBLOCK);