More notes on process supervision

notes/process-supervision.md

@@ -123,3 +123,25 @@ Restart policies and lifecycles: daemontools-encore and nosh both use
 
 Daemontools just always restarts `./run` (after pausing 1 second). s6
 is similar, but runs `./finish` if it exists, before restarting.
+
+Mac OS X "Lion" (?) introduced "sudden termination" at the Cocoa level: apps can indicate they
+are OK with quick shutdown via SIGKILL. There's an analogous `launchd` feature for sudden
+termination of daemons and background Mac processes, though confusingly the docs also say that
+SIGTERM is sent a few seconds before SIGKILL for daemons.
+ - https://developer.apple.com/library/archive/documentation/MacOSX/Conceptual/BPSystemStartup/Chapters/Lifecycle.html
+ - https://developer.apple.com/documentation/foundation/processinfo#1651129
+ - The time delay between SIGTERM and SIGKILL can be controlled (defaults to 20s?):
+    - https://apple.stackexchange.com/a/361723
+
+Oh this is cool! From <https://www.launchd.info/>:
+
+> ## Daemons and Agents
+>
+> launchd differentiates between agents and daemons. The main difference is that an agent is
+> run on behalf of the logged in user while a daemon runs on behalf of the root user or any
+> user you specify with the UserName key.
+
+We have a similar distinction: the "system layer" of supervision vs. programs supervised by
+other portions and/or by inferior syndicate-server instances (like inferior DBus/systemd
+instances). Maybe holding the *conceptual* distinction between agents and daemons is also
+worthwhile!