src/main/org/apache/tools/ant/property/LocalPropertyStack.java

/*
 *  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.
 *
 */
package org.apache.tools.ant.property;

import java.util.Collections;
import java.util.Deque;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.stream.Collector;

import org.apache.tools.ant.PropertyHelper;

/**
 * A stack of local property maps.
 * There is a map for each scope (target, sequential, macro).
 * @since Ant 1.8.0
 */
public class LocalPropertyStack {
    private final Deque<Map<String, Object>> stack = new LinkedList<>();
    private final Object LOCK = new Object();

    // --------------------------------------------------
    //
    //  Local property adding and scoping
    //
    // --------------------------------------------------

    /**
     * Add a local property.
     * @param property the name of the local property.
     */
    public void addLocal(String property) {
        synchronized (LOCK) {
            Map<String, Object> map = stack.peek();
            if (map != null) {
                map.put(property, NullReturn.NULL);
            }
        }
    }

    /**
     * Enter the local scope.
     */
    public void enterScope() {
        synchronized (LOCK) {
            stack.addFirst(new ConcurrentHashMap<>());
        }
    }

    /**
     * Exit the local scope.
     */
    public void exitScope() {
        synchronized (LOCK) {
            stack.removeFirst().clear();
        }
    }

    // --------------------------------------------------
    //
    //  Copy - used in parallel to make a new stack
    //
    // --------------------------------------------------

    /**
     * Copy the stack for a parallel thread.
     * @return a copy.
     */
    public LocalPropertyStack copy() {
        synchronized (LOCK) {
            LocalPropertyStack ret = new LocalPropertyStack();
            ret.stack.addAll(stack);
            return ret;
        }
    }

    // --------------------------------------------------
    //
    //  PropertyHelper delegate methods
    //
    // --------------------------------------------------

    /**
     * Evaluate a property.
     * @param property the property's String "identifier".
     * @param helper the invoking PropertyHelper.
     * @return Object value.
     */
    public Object evaluate(String property, PropertyHelper helper) {
        synchronized (LOCK) {
            for (Map<String, Object> map : stack) {
                Object ret = map.get(property);
                if (ret != null) {
                    return ret;
                }
            }
        }
        return null;
    }

    /**
     * Set a *new" property.
     * @param property the property's String "identifier".
     * @param value    the value to set.
     * @param propertyHelper the invoking PropertyHelper.
     * @return true if this entity 'owns' the property.
     */
    public boolean setNew(
        String property, Object value, PropertyHelper propertyHelper) {
        Map<String, Object> map = getMapForProperty(property);
        if (map == null) {
            return false;
        }
        Object currValue = map.get(property);
        if (currValue == NullReturn.NULL) {
            map.put(property, value);
        }
        return true;
    }

    /**
     * Set a property.
     * @param property the property's String "identifier".
     * @param value    the value to set.
     * @param propertyHelper the invoking PropertyHelper.
     * @return true if this entity 'owns' the property.
     */
    public boolean set(String property, Object value, PropertyHelper propertyHelper) {
        Map<String, Object> map = getMapForProperty(property);
        if (map == null) {
            return false;
        }
        map.put(property, value);
        return true;
    }

    /**
     * Returns the names of all known local properties.
     * @since 1.10.9
     * @return the names of all known local properties.
     */
    public Set<String> getPropertyNames() {
        final Set<String> names = stack.stream().map(Map::keySet)
            .collect(Collector.of(() -> new HashSet<String>(),
                (ns, ks) -> ns.addAll(ks),
                (ns1, ns2) -> { ns1.addAll(ns2); return ns1; },
                Collector.Characteristics.UNORDERED, Collector.Characteristics.IDENTITY_FINISH));
        return Collections.unmodifiableSet(names);
    }

    private Map<String, Object> getMapForProperty(String property) {
        synchronized (LOCK) {
            for (Map<String, Object> map : stack) {
                if (map.get(property) != null) {
                    return map;
                }
            }
        }
        return null;
    }
}