does linux kill() return after the process excute signal handler?

I want use kill() to kill a program. does linux kernel ensure that the program is killed before kill() returned? If not, I have to check whether the program is killed already.

Answer

does linux kernel ensure that the program is killed before kill() returned?

No, kill merely sends a signal to a process or group of processes. Its successful return only tells you that the signal was sent.

The Linux man pages are straightforward about this, clarifying that a successful return means “at least one signal was sent”.

So, this does not tell you whether the signal is blocked/held pending by the target process, was ignored (SIG_IGN), has taken its default action, has been handled, or accepted.