The _lwp_kill() function sends a signal to the LWP specified by target_lwp. The signal that is to be sent is specified by sig and must be one from the list given in signal(3HEAD). If sig is 0 (the null signal), error checking is performed but no signal is actually sent. This can be used to check the validity of target_lwp.
The target_lwp must be an LWP within the same process as the calling LWP.