These functions post a signal to one or more processes. The argument signum common to all three functions should be in the range [1- NSIG].
The psignal function posts signal number signum to the process represented by the process structure p. With a few exceptions noted below, the target process signal disposition is updated and is marked as runnable, so further handling of the signal is done in the context of the target process after a context switch. Note that psignal does not by itself cause a context switch to happen.
The target process is not marked as runnable in the following cases:
- The target process is sleeping uninterruptibly. The signal will be noticed when the process returns from the system call or trap.
- The target process is currently ignoring the signal.
- If a stop signal is sent to a sleeping process that takes the default action (see sigaction(2)), the process is stopped without awakening it.
- SIGCONT restarts a stopped process (or puts them back to sleep) regardless of the signal action (e.g., blocked or ignored).
If the target process is being traced psignal behaves as if the target process were taking the default action for signum. This allows the tracing process to be notified of the signal.
The pgsignal function posts signal number signum to each member of the process group described by pgrp. If checkctty is non-zero, the signal will be posted only to processes that have a controlling terminal. pgsignal is implemented by walking along the process list headed by the field pg_members of the process group structure pointed at by pgrp and calling psignal as appropriate. If pgrp is NULL no action is taken.
The gsignal function posts signal number signum to each member of the process group identified by the group id pgid. gsignal first finds the group structure associated with pgid, then invokes pgsignal with the argument checkctty set to zero. If pgid is zero no action is taken.
sigaction(2), signal(9), tsleep(9)