Designing a monitor process for monitoring and restarting processes

Question

I am designing a monitor process. The job of the monitor process is to monitor a few set of configured processes. When the monitor process detects that a process has gone do

Answer 1

You should not be checking /proc to determine which process has exited - it's possible for another, unrelated, process to start in the meantime and be coincidentally assigned the same PID.

Instead, within your SIGCHLD handler you should use the waitpid() system call, in a loop such as:

int status;
pid_t child;

while ((child = waitpid(-1, &status, WNOHANG)) > 0)
{
    /* Process with PID 'child' has exited, handle it */
}

(The loop is needed because multiple child processes may exit within a short period of time, but only one SIGCHLD may result).