foundation/org.eclipse.persistence.core/src/main/java/org/eclipse/persistence/sessions/server/ReadConnectionPool.java

/*
 * Copyright (c) 1998, 2020 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0,
 * or the Eclipse Distribution License v. 1.0 which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
 */

// Contributors:
//     Oracle - initial API and implementation from Oracle TopLink
package org.eclipse.persistence.sessions.server;

import org.eclipse.persistence.internal.databaseaccess.*;
import org.eclipse.persistence.logging.SessionLog;
import org.eclipse.persistence.sessions.Login;
import org.eclipse.persistence.exceptions.*;

/**
 * <p>
 * <b>Purpose</b>: The read connection pool is used for read access through the server session.
 * Any of the connection pools can be used for the read pool however this is the default.
 * This pool allows for concurrent reads against the same JDBC connection and requires that
 * the JDBC connection support concurrent read access.
 */
public class ReadConnectionPool extends ConnectionPool {

    /**
     * PUBLIC:
     * Build a new read connection pool.
     */
    public ReadConnectionPool() {
        super();
    }

    /**
     * PUBLIC:
     * Build a new read connection pool.
     */
    public ReadConnectionPool(String name, Login login, ServerSession owner) {
        super(name, login, owner);
    }

    /**
     * PUBLIC:
     * Build a new read connection pool.
     */
    public ReadConnectionPool(String name, Login login, int minNumberOfConnections, int maxNumberOfConnections, ServerSession owner) {
        super(name, login, minNumberOfConnections, maxNumberOfConnections, owner);
    }

    /**
     * PUBLIC:
     * Build a new read connection pool.
     */
    public ReadConnectionPool(String name, Login login, int initialNumberOfConnections, int minNumberOfConnections, int maxNumberOfConnections, ServerSession owner) {
        super(name, login, initialNumberOfConnections, minNumberOfConnections, maxNumberOfConnections, owner);
    }

    /**
     * INTERNAL:
     * Wait until a connection is available and allocate the connection for the client.
     */
    @Override
    public synchronized Accessor acquireConnection() throws ConcurrencyException {
        // Check for dead database and fail-over.
        if (this.isDead) {
            return failover();
        }
        Accessor leastBusyConnection = null;

        // Search for an unused connection, also find the least busy in case all are used.
        int size = this.connectionsAvailable.size();
        for (int index = 0; index < size; index++) {
            Accessor connection = this.connectionsAvailable.get(index);
            //if the pool has encountered a connection failure on one of the accessors lets test the others.
            if (this.checkConnections){
                if (this.owner.getLogin().isConnectionHealthValidatedOnError() && this.owner.getServerPlatform().wasFailureCommunicationBased(null, connection, this.owner)){
                    this.connectionsAvailable.remove(index);
                    try {
                        //connection failed connect test
                        connection.closeConnection();
                    } catch (Exception ex){
                        //ignore
                    } finally {
                        connection.releaseCustomizer();
                    }
                    //reset index as we just removed a connection and should check at the same index again
                    --index;
                    //reset size as there are one less connection in the pool now.
                    --size;
                    continue; //skip back to beginning of loop
                } else {
                    this.checkConnections = false;
                }
            }
            if (connection.getCallCount() == 0) {
                leastBusyConnection = connection;
                break;
            }
            if ((leastBusyConnection == null) || (leastBusyConnection.getCallCount() > connection.getCallCount())) {
                leastBusyConnection = connection;
            }
        }

        // If still not at max, add a new connection.
        if (((leastBusyConnection == null) || (leastBusyConnection.getCallCount() != 0))
                    && (this.connectionsAvailable.size() + this.connectionsUsed.size()) < this.maxNumberOfConnections) {
            Accessor connection = null;
            try {
                connection = buildConnection();
            } catch (RuntimeException failed) {
                if (!this.failoverConnectionPools.isEmpty()) {
                    this.isDead = true;
                    this.timeOfDeath = System.currentTimeMillis();
                    this.owner.logThrowable(SessionLog.WARNING, SessionLog.SQL, failed);
                    return acquireConnection();
                } else {
                    throw failed;
                }
            }
            this.connectionsAvailable.add(connection);
            leastBusyConnection = connection;
        }

        // Use the least busy connection.
        leastBusyConnection.incrementCallCount(getOwner());
        if (this.owner.shouldLog(SessionLog.FINEST, SessionLog.CONNECTION)) {
            Object[] args = new Object[1];
            args[0] = this.name;
            this.owner.log(SessionLog.FINEST, SessionLog.CONNECTION, "acquire_connection", args, leastBusyConnection);
        }
        return leastBusyConnection;
    }

    /**
     * INTERNAL:
     * Concurrent reads are supported.
     */
    @Override
    public boolean hasConnectionAvailable() {
        return true;
    }

    /**
     * INTERNAL:
     * Because connections are not exclusive nothing is required.
     */
    @Override
    public synchronized void releaseConnection(Accessor connection) throws DatabaseException {
        if (this.owner.shouldLog(SessionLog.FINEST, SessionLog.CONNECTION)) {
            Object[] args = new Object[1];
            args[0] = this.name;
            this.owner.log(SessionLog.FINEST, SessionLog.CONNECTION, "release_connection", args, connection);
        }
        connection.decrementCallCount();
        if (!connection.isValid()){
            this.checkConnections = true;
            this.connectionsAvailable.remove(connection);
            try{
                connection.disconnect(getOwner());
            }catch (Exception ex){
                //ignore
            }
        }
    }
}