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.misc.env.util;
30 import java.util.LinkedList;
32 import org.onap.aaf.misc.env.APIException;
33 import org.onap.aaf.misc.env.LogTarget;
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
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;
99 * Create a new Pool, given the implementation of Creator<T>, which must be
100 * able to create/destroy T objects at will.
104 public Pool(Creator<T> creator) {
106 this.creator = creator;
107 list = new LinkedList<Pooled<T>>();
111 * Preallocate a certain number of T Objects. Useful for services so that
112 * the first transactions don't get hit with all the Object creation costs
116 * @throws APIException
118 public void prime(LogTarget lt, int prime) throws APIException {
119 for (int i = 0; i < prime; ++i) {
120 Pooled<T> pt = new Pooled<T>(creator.create(), this, lt);
121 synchronized (list) {
130 * Destroy and remove all remaining objects. This is valuable for closing
131 * down all Allocated objects cleanly for exiting. It is also a good method
132 * for removing objects when, for instance, all Objects are invalid because
133 * of broken connections, etc.
135 public void drain() {
136 synchronized (list) {
137 for (int i = 0; i < list.size(); ++i) {
138 Pooled<T> pt = list.remove();
139 creator.destroy(pt.content);
140 pt.logTarget.log("Pool drained ", creator.toString());
148 * This is the essential function for Pool. Get an Object "T" inside a
149 * "Pooled<T>" object. If there is a spare Object, then use it. If not, then
150 * create and pass back.
152 * This one uses a Null LogTarget
154 * IMPORTANT: When the use of this object is done (and the object is still
155 * in a valid state), then "done()" should be called immediately to allow
156 * the object to be reused. That is the point of the Pool...
158 * If the Object is in an invalid state, then "toss()" should be used so the
159 * Pool doesn't pass on invalid objects to others.
163 * @throws APIException
165 public Pooled<T> get() throws APIException {
167 synchronized (list) {
168 if (list.isEmpty()) {
171 pt = list.removeLast();
173 creator.reuse(pt.content);
177 if (spares < max_range)
179 pt = new Pooled<T>(creator.create(), this, LogTarget.NULL);
188 * This is the essential function for Pool. Get an Object "T" inside a
189 * "Pooled<T>" object. If there is a spare Object, then use it. If not, then
190 * create and pass back.
192 * If you don't have access to a LogTarget from Env, use LogTarget.NULL
194 * IMPORTANT: When the use of this object is done (and the object is still
195 * in a valid state), then "done()" should be called immediately to allow
196 * the object to be reused. That is the point of the Pool...
198 * If the Object is in an invalid state, then "toss()" should be used so the
199 * Pool doesn't pass on invalid objects to others.
203 * @throws APIException
205 public Pooled<T> get(LogTarget lt) throws APIException {
207 synchronized (list) {
208 if (list.isEmpty()) {
213 creator.reuse(pt.content);
217 if (spares < max_range)
219 pt = new Pooled<T>(creator.create(), this, lt);
220 lt.log("Pool created ", creator.toString());
229 * This function will validate whether the Objects are still in a usable
230 * state. If not, they are tossed from the Pool. This is valuable to have
231 * when Remote Connections go down, and there is a question on whether the
232 * Pooled Objects are still functional.
236 public boolean validate() {
238 synchronized (list) {
239 for (Pooled<T> t : list) {
240 if (!creator.isValid(t.content)) {
251 * This is an internal method, used only by the Internal Pooled<T> class.
253 * The Pooled<T> class "offers" it's Object back after use. It is an
254 * "offer", because Pool will simply destroy and remove the object if it has
255 * more than enough spares.
261 // Used only by Pooled<T>
262 private boolean offer(LogTarget lt, Pooled<T> used) {
263 if (count < spares) {
264 synchronized (list) {
268 lt.log("Pool recovered ", creator.toString());
270 lt.log("Pool destroyed ", creator.toString());
271 creator.destroy(used.content);
277 * The Creator Interface give the Pool the ability to Create, Destroy and
278 * Validate the Objects it is maintaining. Thus, it is a specially written
279 * Implementation for each type.
285 public interface Creator<T> {
286 public T create() throws APIException;
288 public void destroy(T t);
290 public boolean isValid(T t);
292 public void reuse(T t);
296 * The "Pooled<T>" class is the transient class that wraps the actual Object
297 * T for API use/ It gives the ability to return ("done()", or "toss()") the
298 * Object to the Pool when processing is finished.
300 * For Safety, i.e. to avoid memory leaks and invalid Object States, there
301 * is a "finalize" method. It is strictly for when coder forgets to return
302 * the object, or perhaps hasn't covered the case during Exceptions or
303 * Runtime Exceptions with finally (preferred). This should not be
304 * considered normal procedure, as finalize() is called at an undetermined
305 * time during garbage collection, and is thus rather useless for a Pool.
306 * However, we don't want Coding Mistakes to put the whole program in an
307 * invalid state, so if something happened such that "done()" or "toss()"
308 * were not called, the resource is still cleaned up as well as possible.
314 public static class Pooled<T> {
315 public final T content;
316 private Pool<T> pool;
317 protected LogTarget logTarget;
320 * Create the Wrapping Object Pooled<T>.
326 public Pooled(T t, Pool<T> pool, LogTarget logTarget) {
329 this.logTarget = logTarget;
333 * This is the key API for the Pool, as calling "done()" offers this
334 * object back to the Pool for reuse.
336 * Do not use the Pooled<T> object again after calling "done()".
340 pool.offer(logTarget, this);
345 * The user of the Object may discover that the Object t is no longer in
346 * a valid state. Don't put Garbage back in the Refrigerator... Toss it,
347 * if it's no longer valid.
349 * toss() is also used for draining the Pool, etc.
351 * toss() will attempt to destroy the Object by using the Creator
357 pool.creator.destroy(content);
359 // Don't allow finalize to put it back in.
364 * Just in case someone neglected to offer back object... Do not rely on
365 * this, as there is no specific time when finalize is called, which
366 * rather defeats the purpose of a Pool.
369 protected void finalize() throws Throwable {
378 * Get the maximum number of spare objects allowed at any moment
382 public int getMaxRange() {
387 * Set a Max Range for numbers of spare objects waiting to be used.
389 * No negative numbers are allowed
393 public void setMaxRange(int max_range) {
394 // Do not allow negative numbers
395 this.max_range = Math.max(0, max_range);