/interpreter/tags/at2dist041108/src/edu/vub/at/objects/symbiosis/JMethodCache.java

  1/**
  2 * AmbientTalk/2 Project
  3 * JMethodCache.java created on 9-dec-2006 at 17:14:55
  4 * (c) Programming Technology Lab, 2006 - 2007
  5 * Authors: Tom Van Cutsem & Stijn Mostinckx
  6 * 
  7 * Permission is hereby granted, free of charge, to any person
  8 * obtaining a copy of this software and associated documentation
  9 * files (the "Software"), to deal in the Software without
 10 * restriction, including without limitation the rights to use,
 11 * copy, modify, merge, publish, distribute, sublicense, and/or
 12 * sell copies of the Software, and to permit persons to whom the
 13 * Software is furnished to do so, subject to the following
 14 * conditions:
 15 *
 16 * The above copyright notice and this permission notice shall be
 17 * included in all copies or substantial portions of the Software.
 18 *
 19 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 20 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 21 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 22 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 23 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 24 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 25 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 26 * OTHER DEALINGS IN THE SOFTWARE.
 27 */
 28package edu.vub.at.objects.symbiosis;
 29
 30import java.lang.ref.SoftReference;
 31import java.util.Collections;
 32import java.util.Hashtable;
 33import java.util.Map;
 34
 35/**
 36 * A singleton object that represents a method cache. It is used to speed up
 37 * the symbiosis with Java. Every time a JavaMethod is successfully created from
 38 * an array of java.lang.reflect.Method objects, it is stored in the cache.
 39 * The cache uses weak references such that JavaMethod instances can be safely recollected
 40 * when they are no longer used. Note that this caching scheme only works because:
 41 *  - Java classes are unmodifyable at runtime
 42 *  - JavaMethod objects are constant, so may be safely shared between different actors
 43 * 
 44 * The method cache is implemented as a hash map, mapping pairs
 45 * [ java.lang.Class class, java.lang.String methodname, boolean isStatic ] => soft ref to JavaMethod
 46 * 
 47 * If a JavaMethod has been garbage collected, its entry is removed from the cache.
 48 * Soft references rather than weak references are used to point to the JavaMethod entries.
 49 * Soft references are like weak references, but normally only get reclaimed when the
 50 * JVM runs low on memory. Hence, they are much more suitable for caching.
 51 * 
 52 * The cache is synchronized to ensure proper synchronization between different actors.
 53 * 
 54 * @author tvcutsem
 55 */
 56public final class JMethodCache {
 57	
 58	public static final JMethodCache _INSTANCE_ = new JMethodCache();
 59	
 60	private final Map cache_;
 61	
 62	private JMethodCache() {
 63		cache_ = Collections.synchronizedMap(new Hashtable());
 64	}
 65	
 66	/**
 67	 * Add a JavaMethod instance to the cache.
 68	 */
 69	public void put(Class cls, String methName, boolean isStatic, JavaMethod entry) {
 70		cache_.put(new CacheKey(cls, methName, isStatic), new SoftReference(entry));
 71	}
 72	
 73	/**
 74	 * Retrieve a JavaMethod entry from the cache.
 75	 * @return the entry, or null if the cache does not contain the entry
 76	 */
 77	public JavaMethod get(Class cls, String methName, boolean isStatic) {
 78		CacheKey key = new CacheKey(cls, methName, isStatic);
 79		SoftReference ref = (SoftReference) cache_.get(key);
 80		if (ref == null) {
 81			return null; // cache miss
 82		} else {
 83			JavaMethod entry = (JavaMethod) ref.get();
 84			if (entry != null) {
 85				// cache hit
 86				return entry;
 87			} else {
 88				// entry was garbage-collected, clean up the mapping
 89				cache_.remove(key);
 90				return null; // cache miss
 91			}
 92		}
 93	}
 94	
 95	private static class CacheKey {
 96		private final Class class_;
 97		private final String methodName_;
 98		private final boolean isStatic_;
 99		public CacheKey(Class c, String mname, boolean isStatic) {
100			class_ = c;
101			methodName_ = mname;
102			isStatic_ = isStatic;
103		}
104		
105		public boolean equals(Object other) {
106		    // no check on type of other for performance reasons:
107			// these CacheKeys are not compared to anything else
108			CacheKey otherKey = (CacheKey) other;
109			return ((class_.equals(otherKey.class_))
110					&& (methodName_.equals(otherKey.methodName_))
111					&& (isStatic_ == otherKey.isStatic_));
112		}
113		
114		public int hashCode() {
115			return (class_.hashCode() | methodName_.hashCode()) << ((isStatic_) ? 1 : 0);
116		}
117	}
118
119}