UNIX IPC

[gwyn at brl-vld]

From:      Doug Gwyn (VLD/VMB) <gwyn at brl-vld>

Signals have several bad properties for IPC:
	1.  They break "slow" (i.e. non-disk) i/o in progress
	    (the Berkeley "cure" for this is worse than the disease);
	2.  They reset the signal-catching state to SIG_DFL before
	    dispatching to a signal catcher (trying to fix this would
	    break code that depends on this side-effect);
	3.  Multiple signals do not stack or block the sender.
4.2BSD is supposed to provide a more flexible signal scheme.