EclipsePreferences: use simple HashMap

Using a concurrent Map is a waste as every access is guarded by
childAndPropertyLock anyway.

+ add missing guards (was used unguarded in RootPreferences)
+ make getChild(String key, Object context, boolean create) atomic

bundles/org.eclipse.equinox.preferences/META-INF/MANIFEST.MF

@@ -2,7 +2,7 @@ Manifest-Version: 1.0
 Bundle-ManifestVersion: 2
 Bundle-Name: %pluginName
 Bundle-SymbolicName: org.eclipse.equinox.preferences; singleton:=true
-Bundle-Version: 3.11.100.qualifier
+Bundle-Version: 3.11.200.qualifier
 Bundle-Activator: org.eclipse.core.internal.preferences.Activator
 Bundle-Vendor: %providerName
 Bundle-Localization: plugin

bundles/org.eclipse.equinox.preferences/src/org/eclipse/core/internal/preferences/EclipsePreferences.java

@@ -22,7 +22,6 @@
 import java.nio.file.*;
 import java.nio.file.Path;
 import java.util.*;
-import java.util.concurrent.ConcurrentHashMap;
 import org.eclipse.core.internal.runtime.RuntimeLog;
 import org.eclipse.core.runtime.*;
 import org.eclipse.core.runtime.preferences.*;
@@ -58,8 +57,10 @@ public class EclipsePreferences implements IEclipsePreferences, IScope {
 	private static final String BACKUP_FILE_EXTENSION = ".bak"; //$NON-NLS-1$
 
 	private String cachedPath;
-	protected ImmutableMap properties = ImmutableMap.EMPTY;
-	protected Map<String, Object> children;
+	/** synchronized by childAndPropertyLock */
+	private ImmutableMap properties = ImmutableMap.EMPTY;
+	/** synchronized by childAndPropertyLock */
+	private Map<String, Object> children;
 	/**
 	 * Protects write access to properties and children.
 	 */
@@ -125,12 +126,11 @@ public void accept(IPreferenceNodeVisitor visitor) throws BackingStoreException
 	}
 
 	protected IEclipsePreferences addChild(String childName, IEclipsePreferences child) {
-		// Thread safety: synchronize method to protect modification of children field
 		synchronized (childAndPropertyLock) {
 			if (children == null) {
-				children = new ConcurrentHashMap<>();
+				children = new HashMap<>();
 			}
-			children.put(childName, child == null ? (Object) childName : child);
+			children.put(childName, child == null ? childName : child);
 			return child;
 		}
 	}
@@ -469,7 +469,7 @@ protected boolean childExists(String childName) {
 			if (children == null) {
 				return false;
 			}
-			return children.get(childName) != null;
+			return children.containsKey(childName);
 		}
 	}
 
@@ -493,8 +493,8 @@ protected IEclipsePreferences getChild(String key, Object context, boolean creat
 			if (!create) {
 				return null;
 			}
+			return addChild(key, create(this, key, context));
 		}
-		return addChild(key, create(this, key, context));
 	}
 
 	/**
@@ -1144,4 +1144,29 @@ public String toString() {
 	void setDescriptor(ScopeDescriptor descriptor) {
 		this.descriptor = descriptor;
 	}
+
+	protected IEclipsePreferences getOrCreate(String scope) {
+		IEclipsePreferences child;
+		synchronized (childAndPropertyLock) {
+			if (children == null) {
+				child = null;
+			} else {
+				Object value = children.get(scope);
+				if (value == null) {
+					child = null;
+				} else if (value instanceof IEclipsePreferences eclipsePreferences) {
+					child = eclipsePreferences;
+				} else {
+					// lazy initialization
+					child = PreferencesService.getDefault().createNode(scope);
+					addChild(scope, child);
+				}
+			}
+			if (child == null) {
+				child = new EclipsePreferences(this, scope);
+				addChild(scope, child);
+			}
+		}
+		return child;
+	}
 }

bundles/org.eclipse.equinox.preferences/src/org/eclipse/core/internal/preferences/PreferencesService.java

@@ -128,7 +128,7 @@ public IStatus applyPreferences(IExportedPreferences preferences) throws CoreExc
 
 				// iterate over the preferences in this node and set them
 				// in the global space.
-				String[] keys = epNode.properties.keys();
+				String[] keys = epNode.keys();
 
 				// if this node was removed then we need to create a new one
 				if (removed) {

bundles/org.eclipse.equinox.preferences/src/org/eclipse/core/internal/preferences/RootPreferences.java

@@ -48,23 +48,6 @@ public void flush() throws BackingStoreException {
 		}
 	}
 
-	private synchronized IEclipsePreferences getChild(String key) {
-		if (children == null) {
-			return null;
-		}
-		Object value = children.get(key);
-		if (value == null) {
-			return null;
-		}
-		if (value instanceof IEclipsePreferences eclipsePreferences) {
-			return eclipsePreferences;
-		}
-		// lazy initialization
-		IEclipsePreferences child = PreferencesService.getDefault().createNode(key);
-		addChild(key, child);
-		return child;
-	}
-
 	@Override
 	public Preferences node(String path) {
 		return getNode(path, true); // create if not found
@@ -79,11 +62,7 @@ public Preferences getNode(String path, boolean create) {
 		String scope = path.substring(startIndex, endIndex == -1 ? path.length() : endIndex);
 		IEclipsePreferences child;
 		if (create) {
-			child = getChild(scope);
-			if (child == null) {
-				child = new EclipsePreferences(this, scope);
-				addChild(scope, child);
-			}
+			child = getOrCreate(scope);
 		} else {
 			child = getChild(scope, null, false);
 			if (child == null) {