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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
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package com.sun.jndi.ldap.pool;

import java.util.ArrayList; // JDK 1.2
import java.util.List;

import java.lang.ref.Reference;
import java.lang.ref.SoftReference;

import javax.naming.NamingException;
import javax.naming.InterruptedNamingException;
import javax.naming.CommunicationException;

Represents a list of PooledConnections (actually, ConnectionDescs) with the
same pool id.
The list starts out with an initial number of connections.
Additional PooledConnections are created lazily upon demand.
The list has a maximum size. When the number of connections
reaches the maximum size, a request for a PooledConnection blocks until
a connection is returned to the list. A maximum size of zero means that
there is no maximum: connection creation will be attempted when
no idle connection is available.
The list may also have a preferred size. If the current list size
is less than the preferred size, a request for a connection will result in
a PooledConnection being created (even if an idle connection is available).
If the current list size is greater than the preferred size,
a connection being returned to the list will be closed and removed from
the list. A preferred size of zero means that there is no preferred size:
connections are created only when no idle connection is available and
a connection being returned to the list is not closed. Regardless of the
preferred size, connection creation always observes the maximum size:
a connection won't be created if the list size is at or exceeds the
maximum size.
Author:
Rosanna Lee/**
 * Represents a list of PooledConnections (actually, ConnectionDescs) with the
 * same pool id.
 * The list starts out with an initial number of connections.
 * Additional PooledConnections are created lazily upon demand.
 * The list has a maximum size. When the number of connections
 * reaches the maximum size, a request for a PooledConnection blocks until
 * a connection is returned to the list. A maximum size of zero means that
 * there is no maximum: connection creation will be attempted when
 * no idle connection is available.
 *
 * The list may also have a preferred size. If the current list size
 * is less than the preferred size, a request for a connection will result in
 * a PooledConnection being created (even if an idle connection is available).
 * If the current list size is greater than the preferred size,
 * a connection being returned to the list will be closed and removed from
 * the list. A preferred size of zero means that there is no preferred size:
 * connections are created only when no idle connection is available and
 * a connection being returned to the list is not closed. Regardless of the
 * preferred size, connection creation always observes the maximum size:
 * a connection won't be created if the list size is at or exceeds the
 * maximum size.
 *
 * @author Rosanna Lee
 */

// Package private: accessed only by Pool
final class Connections implements PoolCallback {
    private static final boolean debug = Pool.debug;
    private static final boolean trace =
        com.sun.jndi.ldap.LdapPoolManager.trace;
    private static final int DEFAULT_SIZE = 10;

    final private int maxSize;
    final private int prefSize;
    final private List<ConnectionDesc> conns;

    private boolean closed = false;   // Closed for business
    private Reference<Object> ref; // maintains reference to id to prevent premature GC

    
Params:
id – the identity (connection request) of the connections in the list
initSize – the number of connections to create initially
prefSize – the preferred size of the pool. The pool will try
to maintain a pool of this size by creating and closing connections
as needed.
maxSize – the maximum size of the pool. The pool will not exceed
this size. If the pool is at this size, a request for a connection
will block until an idle connection is released to the pool or
when one is removed.
factory – The factory responsible for creating a connection/**
     * @param id the identity (connection request) of the connections in the list
     * @param initSize the number of connections to create initially
     * @param prefSize the preferred size of the pool. The pool will try
     * to maintain a pool of this size by creating and closing connections
     * as needed.
     * @param maxSize the maximum size of the pool. The pool will not exceed
     * this size. If the pool is at this size, a request for a connection
     * will block until an idle connection is released to the pool or
     * when one is removed.
     * @param factory The factory responsible for creating a connection
     */
    Connections(Object id, int initSize, int prefSize, int maxSize,
        PooledConnectionFactory factory) throws NamingException {

        this.maxSize = maxSize;
        if (maxSize > 0) {
            // prefSize and initSize cannot exceed specified maxSize
            this.prefSize = Math.min(prefSize, maxSize);
            initSize = Math.min(initSize, maxSize);
        } else {
            this.prefSize = prefSize;
        }
        conns = new ArrayList<>(maxSize > 0 ? maxSize : DEFAULT_SIZE);

        // Maintain soft ref to id so that this Connections' entry in
        // Pool doesn't get GC'ed prematurely
        ref = new SoftReference<>(id);

        d("init size=", initSize);
        d("max size=", maxSize);
        d("preferred size=", prefSize);

        // Create initial connections
        PooledConnection conn;
        for (int i = 0; i < initSize; i++) {
            conn = factory.createPooledConnection(this);
            td("Create ", conn ,factory);
            conns.add(new ConnectionDesc(conn)); // Add new idle conn to pool
        }
    }

    
Retrieves a PooledConnection from this list of connections.
Use an existing one if one is idle, or create one if the list's
max size hasn't been reached. If max size has been reached, wait
for a PooledConnection to be returned, or one to be removed (thus
not reaching the max size any longer).
Params:
timeout – if > 0, msec to wait until connection is available
factory – creates the PooledConnection if one needs to be created
Throws:
NamingException – PooledConnection cannot be created, because this
thread was interrupted while it waited for an available connection,
or if it timed out while waiting, or the creation of a connection
resulted in an error.
Returns:
A non-null PooledConnection/**
     * Retrieves a PooledConnection from this list of connections.
     * Use an existing one if one is idle, or create one if the list's
     * max size hasn't been reached. If max size has been reached, wait
     * for a PooledConnection to be returned, or one to be removed (thus
     * not reaching the max size any longer).
     *
     * @param timeout if > 0, msec to wait until connection is available
     * @param factory creates the PooledConnection if one needs to be created
     *
     * @return A non-null PooledConnection
     * @throws NamingException PooledConnection cannot be created, because this
     * thread was interrupted while it waited for an available connection,
     * or if it timed out while waiting, or the creation of a connection
     * resulted in an error.
     */
    synchronized PooledConnection get(long timeout,
        PooledConnectionFactory factory) throws NamingException {
        PooledConnection conn;
        long start = (timeout > 0 ? System.currentTimeMillis() : 0);
        long waittime = timeout;

        d("get(): before");
        while ((conn = getOrCreateConnection(factory)) == null) {
            if (timeout > 0 && waittime <= 0) {
                throw new CommunicationException(
                    "Timeout exceeded while waiting for a connection: " +
                    timeout + "ms");
            }
            try {
                d("get(): waiting");
                if (waittime > 0) {
                    wait(waittime);  // Wait until one is released or removed
                } else {
                    wait();
                }
            } catch (InterruptedException e) {
                throw new InterruptedNamingException(
                    "Interrupted while waiting for a connection");
            }
            // Check whether we timed out
            if (timeout > 0) {
                long now = System.currentTimeMillis();
                waittime = timeout - (now - start);
            }
        }

        d("get(): after");
        return conn;
    }

    
Retrieves an idle connection from this list if one is available.
If none is available, create a new one if maxSize hasn't been reached.
If maxSize has been reached, return null.
Always called from a synchronized method.
/**
     * Retrieves an idle connection from this list if one is available.
     * If none is available, create a new one if maxSize hasn't been reached.
     * If maxSize has been reached, return null.
     * Always called from a synchronized method.
     */
    private PooledConnection getOrCreateConnection(
        PooledConnectionFactory factory) throws NamingException {

        int size = conns.size(); // Current number of idle/nonidle conns
        PooledConnection conn = null;

        if (prefSize <= 0 || size >= prefSize) {
            // If no prefSize specified, or list size already meets or
            // exceeds prefSize, then first look for an idle connection
            ConnectionDesc entry;
            for (int i = 0; i < size; i++) {
                entry = conns.get(i);
                if ((conn = entry.tryUse()) != null) {
                    d("get(): use ", conn);
                    td("Use ", conn);
                    return conn;
                }
            }
        }

        // Check if list size already at maxSize specified
        if (maxSize > 0 && size >= maxSize) {
            return null;   // List size is at limit; cannot create any more
        }

        conn = factory.createPooledConnection(this);
        td("Create and use ", conn, factory);
        conns.add(new ConnectionDesc(conn, true)); // Add new conn to pool

        return conn;
    }

    
Releases connection back into list.
If the list size is below prefSize, the connection may be reused.
If the list size exceeds prefSize, then the connection is closed
and removed from the list.
public because implemented as part of PoolCallback.
/**
     * Releases connection back into list.
     * If the list size is below prefSize, the connection may be reused.
     * If the list size exceeds prefSize, then the connection is closed
     * and removed from the list.
     *
     * public because implemented as part of PoolCallback.
     */
    public synchronized boolean releasePooledConnection(PooledConnection conn) {
        ConnectionDesc entry;
        int loc = conns.indexOf(entry=new ConnectionDesc(conn));

        d("release(): ", conn);

        if (loc >= 0) {
            // Found entry

            if (closed || (prefSize > 0 && conns.size() > prefSize)) {
                // If list size exceeds prefSize, close connection

                d("release(): closing ", conn);
                td("Close ", conn);

                // size must be >= 2 so don't worry about empty list
                conns.remove(entry);
                conn.closeConnection();

            } else {
                d("release(): release ", conn);
                td("Release ", conn);

                // Get ConnectionDesc from list to get correct state info
                entry = conns.get(loc);
                // Return connection to list, ready for reuse
                entry.release();
            }
            notifyAll();
            d("release(): notify");
            return true;
        } else {
            return false;
        }
    }

    
Removes PooledConnection from list of connections.
The closing of the connection is separate from this method.
This method is called usually when the caller encounters an error
when using the connection and wants it removed from the pool.
Returns:
true if conn removed; false if it was not in pool
public because implemented as part of PoolCallback./**
     * Removes PooledConnection from list of connections.
     * The closing of the connection is separate from this method.
     * This method is called usually when the caller encounters an error
     * when using the connection and wants it removed from the pool.
     *
     * @return true if conn removed; false if it was not in pool
     *
     * public because implemented as part of PoolCallback.
     */
    public synchronized boolean removePooledConnection(PooledConnection conn) {
        if (conns.remove(new ConnectionDesc(conn))) {
            d("remove(): ", conn);

            notifyAll();

            d("remove(): notify");
            td("Remove ", conn);

            if (conns.isEmpty()) {
                // Remove softref to make pool entry eligible for GC.
                // Once ref has been removed, it cannot be reinstated.
                ref = null;
            }

            return true;
        } else {
            d("remove(): not found ", conn);
            return false;
        }
    }

    
Goes through all entries in list, removes and closes ones that have been
idle before threshold.
Params:
threshold – an entry idle since this time has expired.
Returns:
true if no more connections in list/**
     * Goes through all entries in list, removes and closes ones that have been
     * idle before threshold.
     *
     * @param threshold an entry idle since this time has expired.
     * @return true if no more connections in list
     */
    boolean expire(long threshold) {
        List<ConnectionDesc> clonedConns;
        synchronized(this) {
            clonedConns = new ArrayList<>(conns);
        }
        List<ConnectionDesc> expired = new ArrayList<>();

        for (ConnectionDesc entry : clonedConns) {
            d("expire(): ", entry);
            if (entry.expire(threshold)) {
                expired.add(entry);
                td("expire(): Expired ", entry);
            }
        }

        synchronized (this) {
            conns.removeAll(expired);
            // Don't need to call notify() because we're
            // removing only idle connections. If there were
            // idle connections, then there should be no waiters.
            return conns.isEmpty();  // whether whole list has 'expired'
        }
    }

    
Called when this instance of Connections has been removed from Pool.
This means that no one can get any pooled connections from this
Connections any longer. Expire all idle connections as of 'now'
and leave indicator so that any in-use connections will be closed upon
their return.
/**
     * Called when this instance of Connections has been removed from Pool.
     * This means that no one can get any pooled connections from this
     * Connections any longer. Expire all idle connections as of 'now'
     * and leave indicator so that any in-use connections will be closed upon
     * their return.
     */
    synchronized void close() {
        expire(System.currentTimeMillis());     // Expire idle connections
        closed = true;   // Close in-use connections when they are returned
    }

    String getStats() {
        int idle = 0;
        int busy = 0;
        int expired = 0;
        long use = 0;
        int len;

        synchronized (this) {
            len = conns.size();

            ConnectionDesc entry;
            for (int i = 0; i < len; i++) {
                entry = conns.get(i);
                use += entry.getUseCount();
                switch (entry.getState()) {
                case ConnectionDesc.BUSY:
                    ++busy;
                    break;
                case ConnectionDesc.IDLE:
                    ++idle;
                    break;
                case ConnectionDesc.EXPIRED:
                    ++expired;
                }
            }
        }
        return "size=" + len + "; use=" + use + "; busy=" + busy
            + "; idle=" + idle + "; expired=" + expired;
    }

    private void d(String msg, Object o1) {
        if (debug) {
            d(msg + o1);
        }
    }

    private void d(String msg, int i) {
        if (debug) {
            d(msg + i);
        }
    }

    private void d(String msg) {
        if (debug) {
            System.err.println(this + "." + msg + "; size: " + conns.size());
        }
    }

    private void td(String msg, Object o1, Object o2) {
        if (trace) { // redo test to avoid object creation
            td(msg + o1 + "[" + o2 + "]");
        }
    }
    private void td(String msg, Object o1) {
        if (trace) { // redo test to avoid object creation
            td(msg + o1);
        }
    }
    private void td(String msg) {
        if (trace) {
            System.err.println(msg);
        }
    }
}