The signal's sender. (correct?)
Possible __group_send_sig_info and specific_send_sig_info return values are as follows;
0 -- The signal is successfully sent to a process, which means that, (1) the signal was ignored by the receiving process, (2) this is a non-RT signal and the system already has one queued, and (3) the signal was successfully added to the sigqueue of the receiving process.
-EAGAIN -- The sigqueue of the receiving process is overflowing, the signal was RT, and the signal was sent by a user using something other than kill.
Possible send_group_sigqueue and send_sigqueue return values are as follows;
0 -- The signal was either successfully added into the sigqueue of the receiving process, or a SI_TIMER entry is already queued (in which case, the overrun count will be simply incremented).
1 -- The signal was ignored by the receiving process.
-1 -- (send_sigqueue only) The task was marked exiting, allowing * posix_timer_event to redirect it to the group leader.