2 * ============LICENSE_START====================================================
4 * ===========================================================================
5 * Copyright (c) 2018 AT&T Intellectual Property. All rights reserved.
6 * ===========================================================================
7 * Licensed under the Apache License, Version 2.0 (the "License");
8 * you may not use this file except in compliance with the License.
9 * You may obtain a copy of the License at
11 * http://www.apache.org/licenses/LICENSE-2.0
13 * Unless required by applicable law or agreed to in writing, software
14 * distributed under the License is distributed on an "AS IS" BASIS,
15 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16 * See the License for the specific language governing permissions and
17 * limitations under the License.
18 * ============LICENSE_END====================================================
28 package org.onap.aaf.cadi.util;
30 import java.util.Iterator;
31 import java.util.LinkedList;
33 import org.onap.aaf.cadi.CadiException;
36 * This Class pools on an As-Needed-Basis any particular kind of class, which is
37 * quite suitable for expensive operations.
39 * The user calls "get" on a Pool, and if a waiting resource (T) is available,
40 * it will be returned. Otherwise, one will be created with the "Creator" class
41 * (must be defined for (T)).
43 * You can Prime the instances to avoid huge startup costs
45 * The returned "Pooled" object simply has to call "done()" and the object is
46 * returned to the pool. If the developer does not return the object, a memory
47 * leak does not occur. There are no references to the object once "get" is
48 * called. However, the developer who does not return the object when done
49 * obviates the point of the pool, as new Objects are created in place of the
50 * Object not returned when another call to "get" is made.
52 * There is a cushion of extra objects, currently defaulted to MAX_RANGE. If the
53 * items returned become higher than the MAX_RANGE, the object is allowed to go
54 * out of scope, and be cleaned up. the default can be changed on a per-pool
57 * Class revamped for CadiExceptions and Access logging 10/4/2017
63 public class Pool<T> {
65 * This is a constant which specified the default maximum number of unused
66 * objects to be held at any given time.
68 private static final int MAX_RANGE = 6; // safety
71 * only Simple List needed.
73 * NOTE TO MAINTAINERS: THIS OBJECT DOES IT'S OWN SYNCHRONIZATION. All
74 * changes that touch list must account for correctly synchronizing list.
76 private LinkedList<Pooled<T>> list;
79 * keep track of how many elements exist, to avoid asking list.
84 * Spares are those Object that are primed and ready to go.
89 * Actual MAX number of spares allowed to hang around. Can be set to
90 * something besides the default MAX_RANGE.
92 private int max_range = MAX_RANGE;
95 * The Creator for this particular pool. It must work for type T.
97 private Creator<T> creator;
102 * Create a new Pool, given the implementation of Creator<T>, which must be
103 * able to create/destroy T objects at will.
107 public Pool(Creator<T> creator) {
109 this.creator = creator;
110 list = new LinkedList<>();
115 * Attach Pool Logging activities to any other Logging Mechanism.
118 public void setLogger(Log logger) {
119 this.logger = logger;
122 public void log(Object ...objects) {
127 * Preallocate a certain number of T Objects. Useful for services so that
128 * the first transactions don't get hit with all the Object creation costs
132 * @throws CadiException
134 public void prime(int prime) throws CadiException {
135 for (int i = 0; i < prime; ++i) {
136 Pooled<T> pt = new Pooled<T>(creator.create(), this);
137 synchronized (list) {
146 * Destroy and remove all remaining objects. This is valuable for closing
147 * down all Allocated objects cleanly for exiting. It is also a good method
148 * for removing objects when, for instance, all Objects are invalid because
149 * of broken connections, etc.
151 public void drain() {
152 synchronized (list) {
153 for (int i = 0; i < list.size(); ++i) {
154 Pooled<T> pt = list.remove();
155 creator.destroy(pt.content);
156 logger.log("Pool drained ", creator.toString());
164 * This is the essential function for Pool. Get an Object "T" inside a
165 * "Pooled<T>" object. If there is a spare Object, then use it. If not, then
166 * create and pass back.
168 * This one uses a Null LogTarget
170 * IMPORTANT: When the use of this object is done (and the object is still
171 * in a valid state), then "done()" should be called immediately to allow
172 * the object to be reused. That is the point of the Pool...
174 * If the Object is in an invalid state, then "toss()" should be used so the
175 * Pool doesn't pass on invalid objects to others.
179 * @throws CadiException
181 public Pooled<T> get() throws CadiException {
183 synchronized (list) {
184 if (list.isEmpty()) {
187 pt = list.removeLast();
189 creator.reuse(pt.content);
193 if (spares < max_range)
195 pt = new Pooled<T>(creator.create(), this);
204 * This function will validate whether the Objects are still in a usable
205 * state. If not, they are tossed from the Pool. This is valuable to have
206 * when Remote Connections go down, and there is a question on whether the
207 * Pooled Objects are still functional.
211 public boolean validate() {
213 synchronized (list) {
214 for (Iterator<Pooled<T>> iter = list.iterator(); iter.hasNext();) {
215 Pooled<T> t = iter.next();
216 if (!creator.isValid(t.content)) {
227 * This is an internal method, used only by the Internal Pooled<T> class.
229 * The Pooled<T> class "offers" it's Object back after use. It is an
230 * "offer", because Pool will simply destroy and remove the object if it has
231 * more than enough spares.
237 // Used only by Pooled<T>
238 private boolean offer(Pooled<T> used) {
239 if (count < spares) {
240 synchronized (list) {
244 logger.log("Pool recovered ", creator);
246 logger.log("Pool destroyed ", creator);
247 creator.destroy(used.content);
253 * The Creator Interface give the Pool the ability to Create, Destroy and
254 * Validate the Objects it is maintaining. Thus, it is a specially written
255 * Implementation for each type.
261 public interface Creator<T> {
262 public T create() throws CadiException;
264 public void destroy(T t);
266 public boolean isValid(T t);
268 public void reuse(T t);
271 public interface Log {
272 public void log(Object ... o);
274 public final static Log NULL = new Log() {
276 public void log(Object ... o) {
281 * The "Pooled<T>" class is the transient class that wraps the actual Object
282 * T for API use/ It gives the ability to return ("done()", or "toss()") the
283 * Object to the Pool when processing is finished.
285 * For Safety, i.e. to avoid memory leaks and invalid Object States, there
286 * is a "finalize" method. It is strictly for when coder forgets to return
287 * the object, or perhaps hasn't covered the case during Exceptions or
288 * Runtime Exceptions with finally (preferred). This should not be
289 * considered normal procedure, as finalize() is called at an undetermined
290 * time during garbage collection, and is thus rather useless for a Pool.
291 * However, we don't want Coding Mistakes to put the whole program in an
292 * invalid state, so if something happened such that "done()" or "toss()"
293 * were not called, the resource is still cleaned up as well as possible.
299 public static class Pooled<T> {
300 public final T content;
301 private Pool<T> pool;
304 * Create the Wrapping Object Pooled<T>.
310 public Pooled(T t, Pool<T> pool) {
317 * This is the key API for the Pool, as calling "done()" offers this
318 * object back to the Pool for reuse.
320 * Do not use the Pooled<T> object again after calling "done()".
329 * The user of the Object may discover that the Object t is no longer in
330 * a valid state. Don't put Garbage back in the Refrigerator... Toss it,
331 * if it's no longer valid.
333 * toss() is also used for draining the Pool, etc.
335 * toss() will attempt to destroy the Object by using the Creator
341 pool.creator.destroy(content);
343 // Don't allow finalize to put it back in.
348 * Just in case someone neglected to offer back object... Do not rely on
349 * this, as there is no specific time when finalize is called, which
350 * rather defeats the purpose of a Pool.
353 protected void finalize() throws Throwable {
362 * Get the maximum number of spare objects allowed at any moment
366 public int getMaxRange() {
371 * Set a Max Range for numbers of spare objects waiting to be used.
373 * No negative numbers are allowed
377 public void setMaxRange(int max_range) {
378 // Do not allow negative numbers
379 this.max_range = Math.max(0, max_range);