--- /dev/null
+/**
+ * ============LICENSE_START====================================================
+ * org.onap.ccsdk
+ * ===========================================================================
+ * Copyright (c) 2023 AT&T Intellectual Property. All rights reserved.
+ * ===========================================================================
+ * Licensed 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
+ *
+ * http://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.
+ * ============LICENSE_END====================================================
+ *
+ */
+
+/*
+ * Pool
+ *
+ * Author: Jonathan
+ * 5/27/2011
+ */
+package org.onap.ccsdk.apps.cadi.util;
+
+import java.util.Iterator;
+import java.util.LinkedList;
+
+import org.onap.ccsdk.apps.cadi.CadiException;
+
+/**
+ * This Class pools on an As-Needed-Basis any particular kind of class, which is
+ * quite suitable for expensive operations.
+ *
+ * The user calls "get" on a Pool, and if a waiting resource (T) is available,
+ * it will be returned. Otherwise, one will be created with the "Creator" class
+ * (must be defined for (T)).
+ *
+ * You can Prime the instances to avoid huge startup costs
+ *
+ * The returned "Pooled" object simply has to call "done()" and the object is
+ * returned to the pool. If the developer does not return the object, a memory
+ * leak does not occur. There are no references to the object once "get" is
+ * called. However, the developer who does not return the object when done
+ * obviates the point of the pool, as new Objects are created in place of the
+ * Object not returned when another call to "get" is made.
+ *
+ * There is a cushion of extra objects, currently defaulted to MAX_RANGE. If the
+ * items returned become higher than the MAX_RANGE, the object is allowed to go
+ * out of scope, and be cleaned up. the default can be changed on a per-pool
+ * basis.
+ *
+ * Class revamped for CadiExceptions and Access logging 10/4/2017
+ *
+ * @author Jonathan
+ *
+ * @param <T>
+ */
+public class Pool<T> {
+ /**
+ * This is a constant which specified the default maximum number of unused
+ * objects to be held at any given time.
+ */
+ public static final int MAX_RANGE = 6; // safety
+
+ /**
+ * Maximum objects, in use or waiting
+ */
+ public static final int MAX_OBJECTS = 20; // assumption for thread
+
+ /**
+ * only Simple List needed.
+ *
+ * NOTE TO MAINTAINERS: THIS OBJECT DOES IT'S OWN SYNCHRONIZATION. All
+ * changes that touch list must account for correctly synchronizing list.
+ */
+ private LinkedList<Pooled<T>> list;
+
+ /**
+ * keep track of how many elements are currently available to use, to avoid asking list.
+ */
+ private int count;
+
+ /**
+ * how many objects have been asked for, but not returned or tossed
+ */
+ private int used;
+
+ /**
+ * Actual MAX number of spares allowed to hang around. Can be set to
+ * something besides the default MAX_RANGE.
+ */
+ private int max_range = MAX_RANGE;
+
+ /**
+ * Actual MAX number of Objects both in use, or waiting.
+ * This does not actually affect the Pool, because the objects, once they leave the pool, are not known until
+ * they are put back with done (offer). It only affects the "overLimit()" function.
+ *
+ * Important... this information is only valid if PooledObjects call "done()" or "toss()".
+ */
+ private int max_objects = MAX_OBJECTS;
+
+ /**
+ * The Creator for this particular pool. It must work for type T.
+ */
+ private Creator<T> creator;
+
+ private Log logger;
+
+ /**
+ * Create a new Pool, given the implementation of Creator<T>, which must be
+ * able to create/destroy T objects at will.
+ *
+ * @param creator
+ */
+ public Pool(Creator<T> creator) {
+ count = used = 0;
+ this.creator = creator;
+ list = new LinkedList<>();
+ logger = Log.NULL;
+ }
+
+ /**
+ * Attach Pool Logging activities to any other Logging Mechanism.
+ * @param logger
+ */
+ public void setLogger(Log logger) {
+ this.logger = logger;
+ // Also reset existing Pooled objects
+ for(Pooled<?> p : list) {
+ if(p.content instanceof LogAware) {
+ ((LogAware)p.content).setLog(logger);
+ } else {
+ break;
+ }
+ }
+ }
+
+ public void log(Log.Type type, Object ...objects) {
+ logger.log(type,objects);
+ }
+
+ /**
+ * Preallocate a certain number of T Objects. Useful for services so that
+ * the first transactions don't get hit with all the Object creation costs
+ *
+ * It is assumed that priming also means that it is the minimum desired available resources. Therefore,
+ * max_range is set to prime, if less than current max_range, if it is default.
+ *
+ * @param lt
+ * @param prime
+ * @throws CadiException
+ */
+ public Pool<T> prime(int prime) throws CadiException {
+ if(max_range == MAX_RANGE && prime<max_range) {
+ max_range = prime;
+ }
+ for (int i = 0; i < prime; ++i) {
+ Pooled<T> pt = new Pooled<T>(creator.create(), this);
+ synchronized (list) {
+ list.addFirst(pt);
+ ++count;
+ ++used;
+ }
+ }
+ return this;
+ }
+
+ /**
+ * Destroy and remove all remaining objects. This is valuable for closing
+ * down all Allocated objects cleanly for exiting. It is also a good method
+ * for removing objects when, for instance, all Objects are invalid because
+ * of broken connections, etc.
+ *
+ * Use in conjunction with setMaxRange to no longer store objects, i.e.
+ *
+ * pool.setMaxRange(0).drain();
+ */
+ public synchronized void drain() {
+ while(list.size()>0) {
+ Pooled<T> pt = list.remove();
+ --used;
+ String name = pt.content.toString();
+ creator.destroy(pt.content);
+ logger.log(Log.Type.debug,"Pool destroyed", name);
+ }
+ count = 0;
+ }
+
+ /**
+ * This is the essential function for Pool. Get an Object "T" inside a
+ * "Pooled<T>" object. If there is a spare Object, then use it. If not, then
+ * create and pass back.
+ *
+ * This one uses a Null LogTarget
+ *
+ * IMPORTANT: When the use of this object is done (and the object is still
+ * in a valid state), then "done()" should be called immediately to allow
+ * the object to be reused. That is the point of the Pool...
+ *
+ * If the Object is in an invalid state, then "toss()" should be used so the
+ * Pool doesn't pass on invalid objects to others.
+ *
+ * @param lt
+ * @return
+ * @throws CadiException
+ */
+ public Pooled<T> get() throws CadiException {
+ Pooled<T> pt;
+ synchronized (list) {
+ pt = list.pollLast();
+ }
+ if (pt == null) {
+ pt = new Pooled<T>(creator.create(), this);
+ ++used;
+ } else {
+ --count;
+ creator.reuse(pt.content);
+ }
+ return pt;
+ }
+
+ /**
+ * This function will validate whether the Objects are still in a usable
+ * state. If not, they are tossed from the Pool. This is valuable to have
+ * when Remote Connections go down, and there is a question on whether the
+ * Pooled Objects are still functional.
+ *
+ * @return
+ */
+ public boolean validate() {
+ boolean rv = true;
+ synchronized (list) {
+ for (Iterator<Pooled<T>> iter = list.iterator(); iter.hasNext();) {
+ Pooled<T> t = iter.next();
+ if (!creator.isValid(t.content)) {
+ rv = false;
+ t.toss();
+ iter.remove();
+ }
+ }
+ }
+ return rv;
+ }
+
+ /**
+ * This is an internal method, used only by the Internal Pooled<T> class.
+ *
+ * The Pooled<T> class "offers" it's Object back after use. It is an
+ * "offer", because Pool will simply destroy and remove the object if it has
+ * more than enough spares.
+ *
+ * @param lt
+ * @param used
+ * @return
+ */
+ // Used only by Pooled<T>
+ private boolean offer(Pooled<T> usedP) {
+ if (count < max_range) {
+ synchronized (list) {
+ list.addFirst(usedP);
+ ++count;
+ }
+ logger.log(Log.Type.trace,"Pool recovered ", creator);
+ } else {
+ destroy(usedP.content);
+ }
+ return false;
+ }
+
+ /**
+ * Destroy, using Creator's specific semantics, the Object, and decrement "used"
+ *
+ * @param t
+ */
+ private void destroy(T t) {
+ creator.destroy(t);
+ synchronized (list) {
+ --used;
+ }
+ logger.log(Log.Type.debug,"Pool destroyed ", creator);
+ }
+
+ /**
+ * The Creator Interface give the Pool the ability to Create, Destroy and
+ * Validate the Objects it is maintaining. Thus, it is a specially written
+ * Implementation for each type.
+ *
+ * @author Jonathan
+ *
+ * @param <T>
+ */
+ public interface Creator<T> {
+ public T create() throws CadiException;
+
+ public void destroy(T t);
+
+ public boolean isValid(T t);
+
+ public void reuse(T t);
+ }
+
+ /**
+ * Pooled Classes can be "Log Aware", which means they can tie into the same
+ * Logging element that the Pool is using. To do this, the Object must implement "LogAware"
+ *
+ * @author Jonathan
+ *
+ */
+ public interface LogAware {
+ public void setLog(Log log);
+ }
+
+ /**
+ * The "Pooled<T>" class is the transient class that wraps the actual Object
+ * T for API use/ It gives the ability to return ("done()", or "toss()") the
+ * Object to the Pool when processing is finished.
+ *
+ * For Safety, i.e. to avoid memory leaks and invalid Object States, there
+ * is a "finalize" method. It is strictly for when coder forgets to return
+ * the object, or perhaps hasn't covered the case during Exceptions or
+ * Runtime Exceptions with finally (preferred). This should not be
+ * considered normal procedure, as finalize() is called at an undetermined
+ * time during garbage collection, and is thus rather useless for a Pool.
+ * However, we don't want Coding Mistakes to put the whole program in an
+ * invalid state, so if something happened such that "done()" or "toss()"
+ * were not called, the resource is still cleaned up as well as possible.
+ *
+ * @author Jonathan
+ *
+ * @param <T>
+ */
+ public static class Pooled<T> {
+ public final T content;
+ private Pool<T> pool;
+
+ /**
+ * Create the Wrapping Object Pooled<T>.
+ *
+ * @param t
+ * @param pool
+ * @param logTarget
+ */
+ public Pooled(T t, Pool<T> pool) {
+ content = t;
+ if(t instanceof LogAware) {
+ ((LogAware)t).setLog(pool.logger);
+ }
+ this.pool = pool;
+ }
+
+ /**
+ * This is the key API for the Pool, as calling "done()" offers this
+ * object back to the Pool for reuse.
+ *
+ * Do not use the Pooled<T> object again after calling "done()".
+ */
+ public void done() {
+ if (pool != null) {
+ pool.offer(this);
+ }
+ }
+
+ /**
+ * The user of the Object may discover that the Object t is no longer in
+ * a valid state. Don't put Garbage back in the Refrigerator... Toss it,
+ * if it's no longer valid.
+ *
+ * toss() is also used for draining the Pool, etc.
+ *
+ * toss() will attempt to destroy the Object by using the Creator
+ * Interface.
+ *
+ */
+ public void toss() {
+ if (pool != null) {
+ pool.destroy(content);
+ }
+ // Don't allow finalize to put it back in.
+ pool = null;
+ }
+
+ /**
+ * Just in case someone neglected to offer back object... Do not rely on
+ * this, as there is no specific time when finalize is called, which
+ * rather defeats the purpose of a Pool.
+ */
+ @Override
+ protected void finalize() throws Throwable {
+ if (pool != null) {
+ done();
+ pool = null;
+ }
+ }
+
+ @Override
+ public String toString() {
+ return content.toString();
+ }
+ }
+
+ /**
+ * Set a Max Range for numbers of spare objects waiting to be used.
+ *
+ * No negative numbers are allowed
+ *
+ * Use in conjunction with drain to no longer store objects, i.e.
+ *
+ * pool.setMaxRange(0).drain();
+ *
+ * @return
+ */
+ public Pool<T> setMaxRange(int max_range) {
+ // Do not allow negative numbers
+ this.max_range = Math.max(0, max_range);
+ return this;
+ }
+
+ /**
+ * Set a Max Range for numbers of spare objects waiting to be used.
+ *
+ * No negative numbers are allowed
+ *
+ * @return
+ */
+ public Pool<T> setMaxObjects(int max_objects) {
+ // Do not allow negative numbers
+ this.max_objects = Math.max(0, max_objects);
+ return this;
+ }
+
+ /**
+ * return whether objects in use or waiting are beyond max allowed
+ *
+ * Pool does not actually stop new creations, but allows this to be used by
+ * other entities to limit number of creations of expensive Objects, like
+ * Thread Pooling
+ *
+ */
+ public boolean tooManyObjects() {
+ return used > max_objects;
+ }
+
+ public String toString() {
+ return String.format("Pool: count(%d), used(%d), max_range(%d), max_objects(%d)",
+ count, used,max_range,max_objects);
+ }
+}
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