Forum: CFEngine Help Subject: Re: Explanation for 3x iteration in a bundle Author: mark Link to topic: https://cfengine.com/forum/read.php?3,24402,24421#msg-24421
I am a little late replying to this, but here is my take, 1. variables and classes are treated specially, due to the possibilty of circular dependences 2. All other promise types are handled by normal ordering While CFEngine is parsing policy, it attempts to resolve and converge the values of variables and classes. Classes might be defined in terms of variables, variables only in certain classes, etc. So it takes a lot of work to resolve complex variable dependences. Because CFEngine automates this somewhat, it "looks as though" common classes get executed without being in the bundlesequence. However this is not the case -- it only looks that way because common bundles generally only contain variables and classes. Adding common bundles to the bundlesequence, gives the code another 3 chances to resolve hanging dependencies. CFEngine then goes through the normal order promises, marking promises as "done", up to a maximum of three times, until all the promises have been marked "done". See for, example, http://source.cfengine.com/websvn/filedetails.php?repname=Cfengine+core&path=%2Ftrunk%2Fexamples%2Funit_ordering.cf and play with to see if this helps. The Puppet guys claimed that they prescheduled a task graph (makespan) for a config run before executing, but this is actually not possible in a configuration system, because the very act of executing the configuration can change the system and the class-contexts on which the policy is based. To avoid the possibility of infinite loops, CFEngine has a cut off at 3 iterations. This is an arbitrary number based on empiricism. You can understand the algorithm as a self-healing/convergent execution tree with a halting safety-cutoff. _______________________________________________ Help-cfengine mailing list Help-cfengine@cfengine.org https://cfengine.org/mailman/listinfo/help-cfengine
