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     psignal, pgsignal, gsignal, tdsignal — post signal to a thread, process, or process group


     #include <sys/types.h>
     #include <sys/signalvar.h>

     psignal(struct proc *p, int signum);

     pgsignal(struct pgrp *pgrp, int signum, int checkctty);

     gsignal(int pgid, int signum);

     tdsignal(struct thread *td, int signum);


     These functions post a signal to a thread or 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

     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.

     The tdsignal() function posts signal number signum to the thread represented by the thread
     structure td.


     sigaction(2), signal(9), tsleep(9)