Re: Signals

Tim Wright (
Wed, 05 Feb 1997 11:15:33 PST

In message <>,"Richard
B. Johnson" writes:

> Now, I have an old version of Unix System V Release 2.0 User Reference
> Manual, Copyright 1983 AT&T Bell Telephone Laboratories, Inc. (<grin>)
> The __first__ real UNIX documentation. Under SIGNAL(2) there are only
> 19 defined signals! Anything outside this range is illegal. However, there
> is also SSIGNAL(4), the "software signals" which are all user defined and,
> according to the documentation, are handled within the 'C' runtime
> library, not the kernel. These are aparently implemented from a "master"
> signal, SIGUSR1, because they explicitly state that when using SSIGNAL,
> the function of SIGUSR1 is undefined.

Unfortunately, there are some major differences with ssignal/gsignal.
First, the System V man page says you can only have 16 of them numbered
Second, (and much more important to my mind) you will notice a conspicuous
lack of pid in the calls. You can only send "signals" to yourself. Not a
great deal of use IMHO.

To be honest, I really don't see the problem. You have SIGUSR1 and SIGUSR2.
You can overload information by other means if necessary, but generally,
relying on signals for "IPC" makes for unreliable, impossible to debug
software (at least that's my experience). There are better ways of
doing this (i.e. the event driven programming model).


Tim Wright, Worldwide Technical Services,         |  Email:
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