| //// |
| Licensed to the Apache Software Foundation (ASF) under one |
| or more contributor license agreements. See the NOTICE file |
| distributed with this work for additional information |
| regarding copyright ownership. The ASF licenses this file |
| to you under the Apache License, Version 2.0 (the |
| "License"); you may not use this file except in compliance |
| with the License. You may obtain a copy of the License at |
| |
| https://www.apache.org/licenses/LICENSE-2.0 |
| |
| Unless required by applicable law or agreed to in writing, |
| software distributed under the License is distributed on an |
| "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| KIND, either express or implied. See the License for the |
| specific language governing permissions and limitations |
| under the License. |
| //// |
| Here are some explanations about the conflict management algorithm in Ivy. |
| |
| First, one should have a good understanding on how Ivy resolves dependencies, and especially |
| transitive dependencies. |
| |
| During the resolve process, Ivy visits each module of the dependency graph. + |
| Let's call each module a *node*, including the module we are trying to resolve dependencies for. |
| |
| Each node should be able to give a conflict manager for a particular ModuleId. + |
| Let's name it *node.cm(mid)*. |
| |
| Each node should be able to maintain a map from ModuleId to a resolved Collection of nodes. |
| This resolved collection will never contain any evicted node FOR the concerned node as far |
| as Ivy knows, depending on where it is in graph visit. + |
| Let's call this map resolved, and the corresponding resolved collection *node.resolved(mid)*. |
| |
| During the visit, Ivy should always know from which node it came to visit another node. Let's call |
| the first node from which Ivy came *node.parent*. Note that this concept is slightly different from |
| node parent, since a node can have several parents in the graph, but there is also one *node.parent* |
| during the visit. |
| |
| Let's say that a conflict manager is able to filter a collection of nodes to return only those |
| that are not evicted. Let's call that *cm.resolveConflicts(collection)*. |
| |
| Let's call *node.dependencies* the collection of direct dependencies of a node. |
| |
| Let's call *node.revision* the module revision id of a node. |
| |
| And now for the algo. This algo attempts to evict nodes on the fly, i.e. during the Ivy visit, |
| to minimize the number of resolved modules, and thus the number of Ivy files to download. |
| |
| It is presented in a very simplified description language, far away from the whole real complexity, |
| but giving a good understanding of how it works. In particular, it completely hides some complexity due |
| to configurations management. |
| |
| [source,java,subs="verbatim,quotes"] |
| ---- |
| resolve(node) { |
| node.resolved(node.mid) = _collection_(node); |
| resolveConflict(node, node.parent, empty); |
| if (!node.evicted && !node.alreadyResolved) { |
| node.loadData(); |
| resolveConflict(node, node.parent, empty); |
| if (!node.evicted) { |
| // actually do resolve |
| foreach (dep in node.dependencies) { |
| resolve(dep); |
| } |
| } |
| } |
| } |
| |
| resolveConflict(node, parent, toevict) { |
| if (node.revision.exact && parent.resolved(node.mid).revision.contains(node.revision)) { |
| // exact revision already in resolved |
| // => job already done |
| return; |
| } |
| if (parent.resolved(node.mid).containsAny(toevict)) { |
| // parent.resolved(node.mid) is not up to date: |
| // recompute resolved from all sub nodes |
| resolved = parent.cm(node.mid).resolveConflicts(parent.dependencies.resolved(node.mid)); |
| } else { |
| resolved = parent.cm(node.mid).resolveConflicts(_collection_(node, parent.resolved(node.mid))); |
| } |
| if (resolved.contains(node)) { |
| // node has been selected for the current parent |
| // we update its eviction... but it can still be evicted by parent ! |
| node.evicted = false; |
| |
| // handle previously selected nodes that are now evicted by this new node |
| toevict = parent.resolved(node.mid) - resolved; |
| foreach (te in toevict) { |
| te.evicted = true; |
| } |
| |
| // it's very important to update resolved BEFORE recompute parent call |
| // to allow it to recompute its resolved collection with correct data |
| // if necessary |
| parent.resolved(node.mid) = resolved; |
| if (parent.parent != null) { |
| resolveConflict(node, parent.parent, toevict); |
| } |
| } else { |
| // node has been evicted for the current parent |
| |
| // it's time to update parent resolved with found resolved... |
| // if they have not been recomputed, it does not change anything |
| parent.resolved(node.mid) = resolved; |
| |
| node.evicted = true; |
| } |
| } |
| ---- |