[MRESOLVER-587] Memory usage improvements (#536)

Do not use `Object` as descriptor key, use dedicated type. And intern the `List<Dependency>` on artifact descriptors. Also introduce "intern"-ing of ArtifactDescriptor dependencies and managedDependencies that is configurable (speed vs memory).

---

https://issues.apache.org/jira/browse/MRESOLVER-587

Author: cstamas

maven-resolver-impl/src/main/java/org/eclipse/aether/internal/impl/collect/DataPool.java

@@ -58,12 +58,23 @@ public final class DataPool {
 
     private static final String CONFIG_PROP_COLLECTOR_POOL_DESCRIPTOR = "aether.dependencyCollector.pool.descriptor";
 
+    private static final String CONFIG_PROP_COLLECTOR_POOL_DEPENDENCY_LISTS =
+            "aether.dependencyCollector.pool.dependencyLists";
+
+    private static final String CONFIG_PROP_COLLECTOR_POOL_INTERN_ARTIFACT_DESCRIPTOR_DEPENDENCIES =
+            "aether.dependencyCollector.pool.internArtifactDescriptorDependencies";
+
+    private static final String CONFIG_PROP_COLLECTOR_POOL_INTERN_ARTIFACT_DESCRIPTOR_MANAGED_DEPENDENCIES =
+            "aether.dependencyCollector.pool.internArtifactDescriptorManagedDependencies";
+
     private static final String ARTIFACT_POOL = DataPool.class.getName() + "$Artifact";
 
     private static final String DEPENDENCY_POOL = DataPool.class.getName() + "$Dependency";
 
     private static final String DESCRIPTORS = DataPool.class.getName() + "$Descriptors";
 
+    private static final String DEPENDENCY_LISTS_POOL = DataPool.class.getName() + "$DependencyLists";
+
     public static final ArtifactDescriptorResult NO_DESCRIPTOR =
             new ArtifactDescriptorResult(new ArtifactDescriptorRequest());
 
@@ -80,7 +91,12 @@ public final class DataPool {
     /**
      * Descriptor interning pool, lives across session (if session carries non-null {@link RepositoryCache}).
      */
-    private final InternPool<Object, Descriptor> descriptors;
+    private final InternPool<DescriptorKey, Descriptor> descriptors;
+
+    /**
+     * {@link Dependency} list interning pool, lives across session (if session carries non-null {@link RepositoryCache}).
+     */
+    private final InternPool<List<Dependency>, List<Dependency>> dependencyLists;
 
     /**
      * Constraint cache, lives during single collection invocation (same as this DataPool instance).
@@ -92,17 +108,29 @@ public final class DataPool {
      */
     private final ConcurrentHashMap<Object, List<DependencyNode>> nodes;
 
+    private final boolean internArtifactDescriptorDependencies;
+
+    private final boolean internArtifactDescriptorManagedDependencies;
+
     @SuppressWarnings("unchecked")
     public DataPool(RepositorySystemSession session) {
         final RepositoryCache cache = session.getCache();
 
+        internArtifactDescriptorDependencies = ConfigUtils.getBoolean(
+                session, false, CONFIG_PROP_COLLECTOR_POOL_INTERN_ARTIFACT_DESCRIPTOR_DEPENDENCIES);
+        internArtifactDescriptorManagedDependencies = ConfigUtils.getBoolean(
+                session, true, CONFIG_PROP_COLLECTOR_POOL_INTERN_ARTIFACT_DESCRIPTOR_MANAGED_DEPENDENCIES);
+
         InternPool<Artifact, Artifact> artifactsPool = null;
         InternPool<Dependency, Dependency> dependenciesPool = null;
-        InternPool<Object, Descriptor> descriptorsPool = null;
+        InternPool<DescriptorKey, Descriptor> descriptorsPool = null;
+        InternPool<List<Dependency>, List<Dependency>> dependencyListsPool = null;
         if (cache != null) {
             artifactsPool = (InternPool<Artifact, Artifact>) cache.get(session, ARTIFACT_POOL);
             dependenciesPool = (InternPool<Dependency, Dependency>) cache.get(session, DEPENDENCY_POOL);
-            descriptorsPool = (InternPool<Object, Descriptor>) cache.get(session, DESCRIPTORS);
+            descriptorsPool = (InternPool<DescriptorKey, Descriptor>) cache.get(session, DESCRIPTORS);
+            dependencyListsPool =
+                    (InternPool<List<Dependency>, List<Dependency>>) cache.get(session, DEPENDENCY_LISTS_POOL);
         }
 
         if (artifactsPool == null) {
@@ -132,9 +160,20 @@ public DataPool(RepositorySystemSession session) {
             }
         }
 
+        if (dependencyListsPool == null) {
+            String dependencyListsPoolType =
+                    ConfigUtils.getString(session, HARD, CONFIG_PROP_COLLECTOR_POOL_DEPENDENCY_LISTS);
+
+            dependencyListsPool = createPool(dependencyListsPoolType);
+            if (cache != null) {
+                cache.put(session, DEPENDENCY_LISTS_POOL, dependencyListsPool);
+            }
+        }
+
         this.artifacts = artifactsPool;
         this.dependencies = dependenciesPool;
         this.descriptors = descriptorsPool;
+        this.dependencyLists = dependencyListsPool;
 
         this.constraints = new ConcurrentHashMap<>(256);
         this.nodes = new ConcurrentHashMap<>(256);
@@ -148,26 +187,36 @@ public Dependency intern(Dependency dependency) {
         return dependencies.intern(dependency, dependency);
     }
 
-    public Object toKey(ArtifactDescriptorRequest request) {
-        return request.getArtifact();
+    public DescriptorKey toKey(ArtifactDescriptorRequest request) {
+        return new DescriptorKey(request.getArtifact());
     }
 
-    public ArtifactDescriptorResult getDescriptor(Object key, ArtifactDescriptorRequest request) {
+    public ArtifactDescriptorResult getDescriptor(DescriptorKey key, ArtifactDescriptorRequest request) {
         Descriptor descriptor = descriptors.get(key);
         if (descriptor != null) {
             return descriptor.toResult(request);
         }
         return null;
     }
 
-    public void putDescriptor(Object key, ArtifactDescriptorResult result) {
+    public void putDescriptor(DescriptorKey key, ArtifactDescriptorResult result) {
+        if (internArtifactDescriptorDependencies) {
+            result.setDependencies(intern(result.getDependencies()));
+        }
+        if (internArtifactDescriptorManagedDependencies) {
+            result.setManagedDependencies(intern(result.getManagedDependencies()));
+        }
         descriptors.intern(key, new GoodDescriptor(result));
     }
 
-    public void putDescriptor(Object key, ArtifactDescriptorException e) {
+    public void putDescriptor(DescriptorKey key, ArtifactDescriptorException e) {
         descriptors.intern(key, BadDescriptor.INSTANCE);
     }
 
+    private List<Dependency> intern(List<Dependency> dependencies) {
+        return dependencyLists.intern(dependencies, dependencies);
+    }
+
     public Object toKey(VersionRangeRequest request) {
         return new ConstraintKey(request);
     }
@@ -202,8 +251,39 @@ public void putChildren(Object key, List<DependencyNode> children) {
         nodes.put(key, children);
     }
 
-    abstract static class Descriptor {
+    public static final class DescriptorKey {
+        private final Artifact artifact;
+        private final int hashCode;
+
+        private DescriptorKey(Artifact artifact) {
+            this.artifact = artifact;
+            this.hashCode = Objects.hashCode(artifact);
+        }
+
+        @Override
+        public boolean equals(Object o) {
+            if (this == o) {
+                return true;
+            }
+            if (o == null || getClass() != o.getClass()) {
+                return false;
+            }
+            DescriptorKey that = (DescriptorKey) o;
+            return Objects.equals(artifact, that.artifact);
+        }
 
+        @Override
+        public int hashCode() {
+            return hashCode;
+        }
+
+        @Override
+        public String toString() {
+            return getClass().getSimpleName() + "{" + "artifact='" + artifact + '\'' + '}';
+        }
+    }
+
+    abstract static class Descriptor {
         public abstract ArtifactDescriptorResult toResult(ArtifactDescriptorRequest request);
     }
 

maven-resolver-impl/src/main/java/org/eclipse/aether/internal/impl/collect/bf/BfDependencyCollector.java

@@ -448,7 +448,7 @@ private ArtifactDescriptorResult resolveCachedArtifactDescriptor(
             RepositorySystemSession session,
             DependencyProcessingContext context,
             Results results) {
-        Object key = pool.toKey(descriptorRequest);
+        DataPool.DescriptorKey key = pool.toKey(descriptorRequest);
         ArtifactDescriptorResult descriptorResult = pool.getDescriptor(key, descriptorRequest);
         if (descriptorResult == null) {
             try {

maven-resolver-impl/src/main/java/org/eclipse/aether/internal/impl/collect/df/DfDependencyCollector.java

@@ -375,7 +375,7 @@ private ArtifactDescriptorResult resolveCachedArtifactDescriptor(
             Dependency d,
             Results results,
             Args args) {
-        Object key = pool.toKey(descriptorRequest);
+        DataPool.DescriptorKey key = pool.toKey(descriptorRequest);
         ArtifactDescriptorResult descriptorResult = pool.getDescriptor(key, descriptorRequest);
         if (descriptorResult == null) {
             try {

maven-resolver-impl/src/test/java/org/eclipse/aether/internal/impl/collect/DataPoolTest.java

@@ -51,7 +51,7 @@ public void testArtifactDescriptorCaching() {
         result.addAlias(new DefaultArtifact("gid:alias:4"));
 
         DataPool pool = newDataPool();
-        Object key = pool.toKey(request);
+        DataPool.DescriptorKey key = pool.toKey(request);
         pool.putDescriptor(key, result);
         ArtifactDescriptorResult cached = pool.getDescriptor(key, request);
         assertNotNull(cached);