Hi,
In an example from Beej's guide to network programming there's the following piece of server code:
Code:
void sigchld_handler(int s)
{
while(waitpid(-1, NULL, WNOHANG) > 0);
}
...
sa.sa_handler = sigchld_handler; // reap all dead processes
sigemptyset(&sa.sa_mask);
sa.sa_flags = SA_RESTART;
if (sigaction(SIGCHLD, &sa, NULL) == -1) {
perror("sigaction");
exit(1);
}
while(1) { // main accept() loop
sin_size = sizeof their_addr;
if ((new_fd = accept(sockfd, (struct sockaddr *)&their_addr, \
&sin_size)) == -1) {
perror("accept");
continue;
}
printf("server: got connection from %s\n", \
inet_ntoa(their_addr.sin_addr));
if (!fork()) { // this is the child process
close(sockfd); // child doesn't need the listener
if (send(new_fd, "Hello, world!\n", 14, 0) == -1)
perror("send");
close(new_fd);
exit(0);
}
close(new_fd); // parent doesn't need this
}
I think I kind of understand how the //reap dead processes block itself works, but how is it ever triggered from within the while(1) loop where the works is being done? I can understand how any present zombie processes may get reaped prior to entering the while(1) loop but not after.
Also if (sigaction(SIGCHLD, &sa, NULL) fails, tell us about it and exit the server all together. Isn't that a bit extreme or is such a thing only supposed to happen to mall-configured services?
Thanks,
heras
edit: I think this may be linux specific so I put it here.