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.LinkedList;
32 import org.onap.aaf.cadi.CadiException;
35 * This Class pools on an As-Needed-Basis any particular kind of class, which is
36 * quite suitable for expensive operations.
38 * The user calls "get" on a Pool, and if a waiting resource (T) is available,
39 * it will be returned. Otherwise, one will be created with the "Creator" class
40 * (must be defined for (T)).
42 * You can Prime the instances to avoid huge startup costs
44 * The returned "Pooled" object simply has to call "done()" and the object is
45 * returned to the pool. If the developer does not return the object, a memory
46 * leak does not occur. There are no references to the object once "get" is
47 * called. However, the developer who does not return the object when done
48 * obviates the point of the pool, as new Objects are created in place of the
49 * Object not returned when another call to "get" is made.
51 * There is a cushion of extra objects, currently defaulted to MAX_RANGE. If the
52 * items returned become higher than the MAX_RANGE, the object is allowed to go
53 * out of scope, and be cleaned up. the default can be changed on a per-pool
56 * Class revamped for CadiExceptions and Access logging 10/4/2017
62 public class Pool<T> {
64 * This is a constant which specified the default maximum number of unused
65 * objects to be held at any given time.
67 private static final int MAX_RANGE = 6; // safety
70 * only Simple List needed.
72 * NOTE TO MAINTAINERS: THIS OBJECT DOES IT'S OWN SYNCHRONIZATION. All
73 * changes that touch list must account for correctly synchronizing list.
75 private LinkedList<Pooled<T>> list;
78 * keep track of how many elements exist, to avoid asking list.
83 * Spares are those Object that are primed and ready to go.
88 * Actual MAX number of spares allowed to hang around. Can be set to
89 * something besides the default MAX_RANGE.
91 private int max_range = MAX_RANGE;
94 * The Creator for this particular pool. It must work for type T.
96 private Creator<T> creator;
101 * Create a new Pool, given the implementation of Creator<T>, which must be
102 * able to create/destroy T objects at will.
106 public Pool(Creator<T> creator) {
108 this.creator = creator;
109 list = new LinkedList<Pooled<T>>();
114 * Attach Pool Logging activities to any other Logging Mechanism.
117 public void setLogger(Log logger) {
118 this.logger = logger;
121 public void log(Object ...objects) {
126 * Preallocate a certain number of T Objects. Useful for services so that
127 * the first transactions don't get hit with all the Object creation costs
131 * @throws CadiException
133 public void prime(int prime) throws CadiException {
134 for (int i = 0; i < prime; ++i) {
135 Pooled<T> pt = new Pooled<T>(creator.create(), this);
136 synchronized (list) {
145 * Destroy and remove all remaining objects. This is valuable for closing
146 * down all Allocated objects cleanly for exiting. It is also a good method
147 * for removing objects when, for instance, all Objects are invalid because
148 * of broken connections, etc.
150 public void drain() {
151 synchronized (list) {
152 for (int i = 0; i < list.size(); ++i) {
153 Pooled<T> pt = list.remove();
154 creator.destroy(pt.content);
155 logger.log("Pool drained ", creator.toString());
163 * This is the essential function for Pool. Get an Object "T" inside a
164 * "Pooled<T>" object. If there is a spare Object, then use it. If not, then
165 * create and pass back.
167 * This one uses a Null LogTarget
169 * IMPORTANT: When the use of this object is done (and the object is still
170 * in a valid state), then "done()" should be called immediately to allow
171 * the object to be reused. That is the point of the Pool...
173 * If the Object is in an invalid state, then "toss()" should be used so the
174 * Pool doesn't pass on invalid objects to others.
178 * @throws CadiException
180 public Pooled<T> get() throws CadiException {
182 synchronized (list) {
183 if (list.isEmpty()) {
186 pt = list.removeLast();
188 creator.reuse(pt.content);
192 if (spares < max_range)
194 pt = new Pooled<T>(creator.create(), this);
203 * This function will validate whether the Objects are still in a usable
204 * state. If not, they are tossed from the Pool. This is valuable to have
205 * when Remote Connections go down, and there is a question on whether the
206 * Pooled Objects are still functional.
210 public boolean validate() {
212 synchronized (list) {
213 for (Pooled<T> t : list) {
214 if (!creator.isValid(t.content)) {
225 * This is an internal method, used only by the Internal Pooled<T> class.
227 * The Pooled<T> class "offers" it's Object back after use. It is an
228 * "offer", because Pool will simply destroy and remove the object if it has
229 * more than enough spares.
235 // Used only by Pooled<T>
236 private boolean offer(Pooled<T> used) {
237 if (count < spares) {
238 synchronized (list) {
242 logger.log("Pool recovered ", creator);
244 logger.log("Pool destroyed ", creator);
245 creator.destroy(used.content);
251 * The Creator Interface give the Pool the ability to Create, Destroy and
252 * Validate the Objects it is maintaining. Thus, it is a specially written
253 * Implementation for each type.
259 public interface Creator<T> {
260 public T create() throws CadiException;
262 public void destroy(T t);
264 public boolean isValid(T t);
266 public void reuse(T t);
269 public interface Log {
270 public void log(Object ... o);
272 public final static Log NULL = new Log() {
274 public void log(Object ... o) {
279 * The "Pooled<T>" class is the transient class that wraps the actual Object
280 * T for API use/ It gives the ability to return ("done()", or "toss()") the
281 * Object to the Pool when processing is finished.
283 * For Safety, i.e. to avoid memory leaks and invalid Object States, there
284 * is a "finalize" method. It is strictly for when coder forgets to return
285 * the object, or perhaps hasn't covered the case during Exceptions or
286 * Runtime Exceptions with finally (preferred). This should not be
287 * considered normal procedure, as finalize() is called at an undetermined
288 * time during garbage collection, and is thus rather useless for a Pool.
289 * However, we don't want Coding Mistakes to put the whole program in an
290 * invalid state, so if something happened such that "done()" or "toss()"
291 * were not called, the resource is still cleaned up as well as possible.
297 public static class Pooled<T> {
298 public final T content;
299 private Pool<T> pool;
302 * Create the Wrapping Object Pooled<T>.
308 public Pooled(T t, Pool<T> pool) {
315 * This is the key API for the Pool, as calling "done()" offers this
316 * object back to the Pool for reuse.
318 * Do not use the Pooled<T> object again after calling "done()".
327 * The user of the Object may discover that the Object t is no longer in
328 * a valid state. Don't put Garbage back in the Refrigerator... Toss it,
329 * if it's no longer valid.
331 * toss() is also used for draining the Pool, etc.
333 * toss() will attempt to destroy the Object by using the Creator
339 pool.creator.destroy(content);
341 // Don't allow finalize to put it back in.
346 * Just in case someone neglected to offer back object... Do not rely on
347 * this, as there is no specific time when finalize is called, which
348 * rather defeats the purpose of a Pool.
351 protected void finalize() throws Throwable {
360 * Get the maximum number of spare objects allowed at any moment
364 public int getMaxRange() {
369 * Set a Max Range for numbers of spare objects waiting to be used.
371 * No negative numbers are allowed
375 public void setMaxRange(int max_range) {
376 // Do not allow negative numbers
377 this.max_range = Math.max(0, max_range);