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*[[UNIX]] signals* are a means to asynchronously invoke a specific function
(*signal handler*) in a [[process]].  It's a rather limited form of doing
[[IPC]].

Signalling may impact on [[system call]]s that are executing at the same time
in that they may be completely aborted, return incomplete results, scheduled
for restarting, or cause signal delivery to be blocked upon the system call's
completion.

An explanation can be found in the relevant standards, an overview, including
UNIX signals' deficiencies is given in {{$unix#2010_brown_ghosts_3}}, for
example.

In a GNU/Hurd system, the signalling system is [[implemented in
glibc|glibc/signal]].


# Further Reading

  * [[!wikipedia Signal_(computing)]]

  * {{$unix#djb_self-pipe}}.

  * {{$unix#rjk_fork}}.