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