Re: Draft spec for new dpkg "triggers" feature

[Ian Jackson <ian@davenant.greenend.org.uk>]

Andreas Barth writes ("Re: Draft spec for new dpkg "triggers" feature"):
> Consider package foo depends on package bar, and package bar is
> triggered by a file installed by package foo. Does this work?
> 
> Currently, the sequence would be:
> unpack foo bar
> configure bar
> configure foo

Note that `configure foo' probably involves foo's postinst running
`update-bar'.

> How would this sequence be in future?

  unpack foo bar
  configure bar
  configure foo
  postinst bar triggers

>  Would that be considered an cyclic dependency, and broken at
> random?

No, triggers are completely separate to the normal dependency graph.
Note that since unconfigured packages aren't interested in triggers,
the trigger graph never needs to interact with the dependency graph.

dpkg doesn't attempt to compute the graph of the a-triggers-b
relation; instead, it just processes triggers as necessary and detects
cycles if they occur.

Ian.