src/java.base/share/classes/sun/net/www/http/KeepAliveCache.java

/*
 * Copyright (c) 1996, 2021, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
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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).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package sun.net.www.http;

import java.io.IOException;
import java.io.NotSerializableException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.URL;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

import jdk.internal.misc.InnocuousThread;
import sun.security.action.GetIntegerAction;

/**
 * A class that implements a cache of idle Http connections for keep-alive
 *
 * @author Stephen R. Pietrowicz (NCSA)
 * @author Dave Brown
 */
public class KeepAliveCache
    extends HashMap<KeepAliveKey, ClientVector>
    implements Runnable {
    @java.io.Serial
    private static final long serialVersionUID = -2937172892064557949L;

    /* maximum # keep-alive connections to maintain at once
     * This should be 2 by the HTTP spec, but because we don't support pipe-lining
     * a larger value is more appropriate. So we now set a default of 5, and the value
     * refers to the number of idle connections per destination (in the cache) only.
     * It can be reset by setting system property "http.maxConnections".
     */
    static final int MAX_CONNECTIONS = 5;
    static int result = -1;
    @SuppressWarnings("removal")
    static int getMaxConnections() {
        if (result == -1) {
            result = AccessController.doPrivileged(
                new GetIntegerAction("http.maxConnections", MAX_CONNECTIONS))
                .intValue();
            if (result <= 0) {
                result = MAX_CONNECTIONS;
            }
        }
        return result;
    }

    static final int LIFETIME = 5000;

    // This class is never serialized (see writeObject/readObject).
    private final ReentrantLock cacheLock = new ReentrantLock();
    private Thread keepAliveTimer = null;

    /**
     * Constructor
     */
    public KeepAliveCache() {}

    /**
     * Register this URL and HttpClient (that supports keep-alive) with the cache
     * @param url  The URL contains info about the host and port
     * @param http The HttpClient to be cached
     */
    @SuppressWarnings("removal")
    public void put(final URL url, Object obj, HttpClient http) {
        cacheLock.lock();
        try {
            boolean startThread = (keepAliveTimer == null);
            if (!startThread) {
                if (!keepAliveTimer.isAlive()) {
                    startThread = true;
                }
            }
            if (startThread) {
                clear();
                /* Unfortunately, we can't always believe the keep-alive timeout we got
                 * back from the server.  If I'm connected through a Netscape proxy
                 * to a server that sent me a keep-alive
                 * time of 15 sec, the proxy unilaterally terminates my connection
                 * The robustness to get around this is in HttpClient.parseHTTP()
                 */
                final KeepAliveCache cache = this;
                AccessController.doPrivileged(new PrivilegedAction<>() {
                    public Void run() {
                        keepAliveTimer = InnocuousThread.newSystemThread("Keep-Alive-Timer", cache);
                        keepAliveTimer.setDaemon(true);
                        keepAliveTimer.setPriority(Thread.MAX_PRIORITY - 2);
                        keepAliveTimer.start();
                        return null;
                    }
                });
            }

            KeepAliveKey key = new KeepAliveKey(url, obj);
            ClientVector v = super.get(key);

            if (v == null) {
                int keepAliveTimeout = http.getKeepAliveTimeout();
                v = new ClientVector(keepAliveTimeout > 0 ?
                        keepAliveTimeout * 1000 : LIFETIME);
                v.put(http);
                super.put(key, v);
            } else {
                v.put(http);
            }
        } finally {
            cacheLock.unlock();
        }
    }

    /* remove an obsolete HttpClient from its VectorCache */
    public void remove(HttpClient h, Object obj) {
        cacheLock.lock();
        try {
            KeepAliveKey key = new KeepAliveKey(h.url, obj);
            ClientVector v = super.get(key);
            if (v != null) {
                v.remove(h);
                if (v.isEmpty()) {
                    removeVector(key);
                }
            }
        } finally {
            cacheLock.unlock();
        }
    }

    /* called by a clientVector thread when all its connections have timed out
     * and that vector of connections should be removed.
     */
    private void removeVector(KeepAliveKey k) {
        assert cacheLock.isHeldByCurrentThread();
        super.remove(k);
    }

    /**
     * Check to see if this URL has a cached HttpClient
     */
    public HttpClient get(URL url, Object obj) {
        cacheLock.lock();
        try {
            KeepAliveKey key = new KeepAliveKey(url, obj);
            ClientVector v = super.get(key);
            if (v == null) { // nothing in cache yet
                return null;
            }
            return v.get();
        } finally {
            cacheLock.unlock();
        }
    }

    /* Sleeps for an alloted timeout, then checks for timed out connections.
     * Errs on the side of caution (leave connections idle for a relatively
     * short time).
     */
    @Override
    public void run() {
        do {
            try {
                Thread.sleep(LIFETIME);
            } catch (InterruptedException e) {}

            // Remove all outdated HttpClients.
            cacheLock.lock();
            try {
                long currentTime = System.currentTimeMillis();
                List<KeepAliveKey> keysToRemove = new ArrayList<>();

                for (KeepAliveKey key : keySet()) {
                    ClientVector v = get(key);
                    v.lock();
                    try {
                        KeepAliveEntry e = v.peek();
                        while (e != null) {
                            if ((currentTime - e.idleStartTime) > v.nap) {
                                v.poll();
                                e.hc.closeServer();
                            } else {
                                break;
                            }
                            e = v.peek();
                        }

                        if (v.isEmpty()) {
                            keysToRemove.add(key);
                        }
                    } finally {
                        v.unlock();
                    }
                }

                for (KeepAliveKey key : keysToRemove) {
                    removeVector(key);
                }
            } finally {
                cacheLock.unlock();
            }
        } while (!isEmpty());
    }

    /*
     * Do not serialize this class!
     */
    @java.io.Serial
    private void writeObject(ObjectOutputStream stream) throws IOException {
        throw new NotSerializableException();
    }

    @java.io.Serial
    private void readObject(ObjectInputStream stream)
        throws IOException, ClassNotFoundException
    {
        throw new NotSerializableException();
    }
}

/* FILO order for recycling HttpClients, should run in a thread
 * to time them out.  If > maxConns are in use, block.
 */
class ClientVector extends ArrayDeque<KeepAliveEntry> {
    @java.io.Serial
    private static final long serialVersionUID = -8680532108106489459L;
    private final ReentrantLock lock = new ReentrantLock();

    // sleep time in milliseconds, before cache clear
    int nap;

    ClientVector(int nap) {
        this.nap = nap;
    }

    HttpClient get() {
        lock();
        try {
            if (isEmpty()) {
                return null;
            }

            // Loop until we find a connection that has not timed out
            HttpClient hc = null;
            long currentTime = System.currentTimeMillis();
            do {
                KeepAliveEntry e = pop();
                if ((currentTime - e.idleStartTime) > nap) {
                    e.hc.closeServer();
                } else {
                    hc = e.hc;
                }
            } while ((hc == null) && (!isEmpty()));
            return hc;
        } finally {
            unlock();
        }
    }

    /* return a still valid, unused HttpClient */
    void put(HttpClient h) {
        lock();
        try {
            if (size() >= KeepAliveCache.getMaxConnections()) {
                h.closeServer(); // otherwise the connection remains in limbo
            } else {
                push(new KeepAliveEntry(h, System.currentTimeMillis()));
            }
        } finally {
            unlock();
        }
    }

    /* remove an HttpClient */
    boolean remove(HttpClient h) {
        lock();
        try {
            for (KeepAliveEntry curr : this) {
                if (curr.hc == h) {
                    return super.remove(curr);
                }
            }
            return false;
        } finally {
            unlock();
        }
    }

    final void lock() {
        lock.lock();
    }

    final void unlock() {
        lock.unlock();
    }

    /*
     * Do not serialize this class!
     */
    @java.io.Serial
    private void writeObject(ObjectOutputStream stream) throws IOException {
        throw new NotSerializableException();
    }

    @java.io.Serial
    private void readObject(ObjectInputStream stream)
        throws IOException, ClassNotFoundException
    {
        throw new NotSerializableException();
    }
}

class KeepAliveKey {
    private String      protocol = null;
    private String      host = null;
    private int         port = 0;
    private Object      obj = null; // additional key, such as socketfactory

    /**
     * Constructor
     *
     * @param url the URL containing the protocol, host and port information
     */
    public KeepAliveKey(URL url, Object obj) {
        this.protocol = url.getProtocol();
        this.host = url.getHost();
        this.port = url.getPort();
        this.obj = obj;
    }

    /**
     * Determine whether or not two objects of this type are equal
     */
    @Override
    public boolean equals(Object obj) {
        if ((obj instanceof KeepAliveKey) == false)
            return false;
        KeepAliveKey kae = (KeepAliveKey)obj;
        return host.equals(kae.host)
            && (port == kae.port)
            && protocol.equals(kae.protocol)
            && this.obj == kae.obj;
    }

    /**
     * The hashCode() for this object is the string hashCode() of
     * concatenation of the protocol, host name and port.
     */
    @Override
    public int hashCode() {
        String str = protocol+host+port;
        return this.obj == null? str.hashCode() :
            str.hashCode() + this.obj.hashCode();
    }
}

class KeepAliveEntry {
    HttpClient hc;
    long idleStartTime;

    KeepAliveEntry(HttpClient hc, long idleStartTime) {
        this.hc = hc;
        this.idleStartTime = idleStartTime;
    }
}