runtime-config: Require serial hook execution

wking · wking · commit 330223b31a5d · 2015-12-10T20:42:10.000-08:00
Extend [1,2,3] to avoid: hook 1: spawn ---------------> reaped hook 2: spawn ----------------> reaped hook 3: spawn -----> reaped and explicitly require: hook 1: spawn --> reaped hook 2: spawn --> reaped hook 3: spawn --> reaped Folks who do want parallel execution are free to use a parallelizing wrapper: hook 1: spawn ---------------------------> reaped child 1 -----> reaped child 2 ---------> reaped child 3 ---> reaped Although that cuts both ways (with parallel hooks, folks could always use a single hook with a serializing wrapper). Still, I'd guess most current implementations are already taking the serialized approach, so it makes bundle-author life easier if we are explicit about that. [1]: #20 (comment) [2]: #156 [3]: #157 Signed-off-by: W. Trevor King <wking@tremily.us>
diff --git a/runtime-config.md b/runtime-config.md
@@ -10,7 +10,7 @@ Presently there are `Prestart`, `Poststart` and `Poststop`.
 * [`Poststop`](#poststop) is a list of hooks to be run after the container process exits
 
 Hooks allow one to run code before/after various lifecycle events of the container.
-Hooks MUST be called in the listed order.
+Hooks MUST be called in the listed order, with each hook process being reaped before the next hook is executed.
 The state of the container is passed to the hooks over stdin, so the hooks could get the information they need to do their work.
 
 Hook paths are absolute and are executed from the host's filesystem.
