Tracking the death of a child process

Question

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

Answer 1

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.