How could I track down the death of a child process without making the parent process wait until the child process got killed?
I am trying a client-server scenario where the server accepts the connection from a client and forks a new process for each and every connection it accepts.
I am ignoring SIGCHLD signals to prevent zombie creation.
signal(SIGCHLD, SIG_IGN);
while(1)
{
accept();
clients++;
if(fork() ==0)
{
childfunction();
clients--;
}
else
{
}
}
The problem in the above scenario is that if the child process gets killed in the childfunction()
function, the global variable clients
is not getting decremented.
NOTE: I am looking for a solution without using SIGCHLD signal ... If possible
Typically you write a handler for SIGCHLD
which calls waitpid()
on pid -1
. You can use the return value from that to determine what pid died. For example:
void my_sigchld_handler(int sig)
{
pid_t p;
int status;
while ((p=waitpid(-1, &status, WNOHANG)) != -1)
{
/* Handle the death of pid p */
}
}
/* It's better to use sigaction() over signal(). You won't run into the
* issue where BSD signal() acts one way and Linux or SysV acts another. */
struct sigaction sa;
memset(&sa, 0, sizeof(sa));
sa.sa_handler = my_sigchld_handler;
sigaction(SIGCHLD, &sa, NULL);
Alternatively you can call waitpid(pid, &status, 0)
with the child's process ID specified, and synchronously wait for it to die. Or use WNOHANG
to check its status without blocking.