SIGCHLD sended by another process to parent

Question

Let's assume that our process creates a child and then calls wait().

When I try to send signal() or do

kill -SIGCHLD <PID> 

nothing happens at all.

So the question is: How does the process in Linux determine that signal SIGCHLD hadn't been sent by the child? Or, maybe, there is some another mechanism?

Answer 1

The kernel takes care of this.

wait() is not a signal handler listening for (any) SIGCHLD sent to a process, as it might be established via sigaction() or signal().

From wait()'s POSIX spec (emphasis by me):

The wait() and waitpid() functions shall obtain status information pertaining to one of the caller's child processes.