Refine performance

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

@@ -513,7 +513,8 @@ static final class GraphKey {
             this.traverser = traverser;
             this.filter = filter;
 
-            hashCode = Objects.hash(artifact, repositories, selector, manager, traverser, filter);
+            hashCode =
+                    Objects.hash(artifact, repositories, selector, System.identityHashCode(manager), traverser, filter);
         }
 
         @Override

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

@@ -119,11 +119,11 @@ public class BfDependencyCollector extends DependencyCollectorDelegate {
     public static final String CONFIG_PROP_THREADS = CONFIG_PROPS_PREFIX + "threads";
 
     /**
-     * The default value for {@link #CONFIG_PROP_THREADS}, default value 5.
+     * The default value for {@link #CONFIG_PROP_THREADS}, default value {@code Runtime.getRuntime().availableProcessors()}.
      *
      * @since 1.9.0
      */
-    public static final int DEFAULT_THREADS = 5;
+    public static final int DEFAULT_THREADS = Runtime.getRuntime().availableProcessors();
 
     @Inject
     public BfDependencyCollector(
@@ -470,19 +470,28 @@ private ArtifactDescriptorResult resolveDescriptorForVersion(
     }
 
     static class ParallelDescriptorResolver implements Closeable {
-        private final ExecutorService executorService;
+        private static volatile ExecutorService executorService;
 
         /**
          * Artifact ID -> Future of DescriptorResolutionResult
          */
         private final Map<String, Future<DescriptorResolutionResult>> results = new ConcurrentHashMap<>(256);
 
         ParallelDescriptorResolver(int threads) {
-            this.executorService = ExecutorUtils.threadPool(threads, getClass().getSimpleName() + "-");
+            if (executorService == null) {
+                synchronized (ParallelDescriptorResolver.class) {
+                    if (executorService == null) {
+                        // create only once, so that we can reuse it across multiple instances of this class
+                        // and avoid creating too many threads / recreating it for too many times
+                        executorService = ExecutorUtils.threadPool(
+                                threads, ParallelDescriptorResolver.class.getSimpleName() + "-");
+                    }
+                }
+            }
         }
 
         void resolveDescriptors(Artifact artifact, Callable<DescriptorResolutionResult> callable) {
-            results.computeIfAbsent(ArtifactIdUtils.toId(artifact), key -> this.executorService.submit(callable));
+            results.computeIfAbsent(ArtifactIdUtils.toId(artifact), key -> executorService.submit(callable));
         }
 
         void cacheVersionRangeDescriptor(Artifact artifact, DescriptorResolutionResult resolutionResult) {
@@ -494,9 +503,7 @@ Future<DescriptorResolutionResult> find(Artifact artifact) {
         }
 
         @Override
-        public void close() {
-            executorService.shutdown();
-        }
+        public void close() {}
     }
 
     static class DoneFuture<V> implements Future<V> {

maven-resolver-util/src/main/java/org/eclipse/aether/util/graph/manager/AbstractDependencyManager.java

@@ -74,7 +74,7 @@ public abstract class AbstractDependencyManager implements DependencyManager {
 
     protected final SystemDependencyScope systemDependencyScope;
 
-    private final int hashCode;
+    private volatile long hashCode = Long.MAX_VALUE;
 
     protected AbstractDependencyManager(int deriveUntil, int applyFrom, ScopeManager scopeManager) {
         this(
@@ -112,16 +112,6 @@ protected AbstractDependencyManager(
         this.managedExclusions = requireNonNull(managedExclusions);
         // nullable: if using scope manager, but there is no system scope defined
         this.systemDependencyScope = systemDependencyScope;
-
-        this.hashCode = Objects.hash(
-                depth,
-                deriveUntil,
-                applyFrom,
-                managedVersions,
-                managedScopes,
-                managedOptionals,
-                managedLocalPaths,
-                managedExclusions);
     }
 
     protected abstract DependencyManager newInstance(
@@ -332,7 +322,20 @@ public boolean equals(Object obj) {
 
     @Override
     public int hashCode() {
-        return hashCode;
+        if (this.hashCode != Long.MAX_VALUE) {
+            return (int) hashCode;
+        }
+        int result = Objects.hash(
+                depth,
+                deriveUntil,
+                applyFrom,
+                managedVersions,
+                managedScopes,
+                managedOptionals,
+                managedLocalPaths,
+                managedExclusions);
+        this.hashCode = result;
+        return result;
     }
 
     protected static class Key {

maven-resolver-util/src/main/java/org/eclipse/aether/util/graph/manager/MMap.java

@@ -80,11 +80,10 @@ public boolean equals(Object o) {
     }
 
     private static class DoneMMap<K, V> extends MMap<K, V> {
-        private final int hashCode;
+        private volatile long hashCode = Long.MAX_VALUE;
 
         private DoneMMap(HashMap<K, V> delegate) {
             super(delegate);
-            this.hashCode = delegate.hashCode();
         }
 
         @Override
@@ -99,7 +98,12 @@ public MMap<K, V> done() {
 
         @Override
         public int hashCode() {
-            return hashCode;
+            if (this.hashCode != Long.MAX_VALUE) {
+                return (int) hashCode;
+            }
+            int result = delegate.hashCode();
+            this.hashCode = result;
+            return result;
         }
 
         @Override