/*

 * Copyright (c) 1996, 2013, 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.

 *

 * 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

 * or visit www.oracle.com if you need additional information or have any

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 */

package sun.rmi.transport;

import java.rmi.Remote;

import java.rmi.RemoteException;

import java.rmi.dgc.DGC;

import java.rmi.dgc.Lease;

import java.rmi.dgc.VMID;

import java.rmi.server.LogStream;

import java.rmi.server.ObjID;

import java.rmi.server.RemoteServer;

import java.rmi.server.ServerNotActiveException;

import java.security.AccessController;

import java.security.PrivilegedAction;

import java.util.ArrayList;

import java.util.HashSet;

import java.util.HashMap;

import java.util.Iterator;

import java.util.List;

import java.util.Map;

import java.util.Set;

import java.util.concurrent.Future;

import java.util.concurrent.ScheduledExecutorService;

import java.util.concurrent.TimeUnit;

import sun.rmi.runtime.Log;

import sun.rmi.runtime.RuntimeUtil;

import sun.rmi.server.UnicastRef;

import sun.rmi.server.UnicastServerRef;

import sun.rmi.server.Util;

/**

 * This class implements the guts of the server-side distributed GC

 * algorithm

 *

 * @author Ann Wollrath

 */

@SuppressWarnings("deprecation")

final class DGCImpl implements DGC {

    /* dgc system log */

    static final Log dgcLog = Log.getLog("sun.rmi.dgc", "dgc",

        LogStream.parseLevel(AccessController.doPrivileged(

            (PrivilegedAction<String>) () -> System.getProperty("sun.rmi.dgc.logLevel"))));

    /** lease duration to grant to clients */

    private static final long leaseValue =              // default 10 minutes

        AccessController.doPrivileged(

            (PrivilegedAction<Long>) () -> Long.getLong("java.rmi.dgc.leaseValue", 600000));

    /** lease check interval; default is half of lease grant duration */

    private static final long leaseCheckInterval =

        AccessController.doPrivileged(

            (PrivilegedAction<Long>) () -> Long.getLong("sun.rmi.dgc.checkInterval", leaseValue / 2));

    /** thread pool for scheduling delayed tasks */

    private static final ScheduledExecutorService scheduler =

        AccessController.doPrivileged(

            new RuntimeUtil.GetInstanceAction()).getScheduler();

    /** remote implementation of DGC interface for this VM */

    private static DGCImpl dgc;

    /** table that maps VMID to LeaseInfo */

    private Map<VMID,LeaseInfo> leaseTable = new HashMap<>();

    /** checks for lease expiration */

    private Future<?> checker = null;

    /**

     * Return the remote implementation of the DGC interface for

     * this VM.

     */

    static DGCImpl getDGCImpl() {

        return dgc;

    }

    /**

     * Construct a new server-side remote object collector at

     * a particular port. Disallow construction from outside.

     */

    private DGCImpl() {}

    /**

     * The dirty call adds the VMID "vmid" to the set of clients

     * that hold references to the object associated with the ObjID

     * id.  The long "sequenceNum" is used to detect late dirty calls.  If

     * the VMID "vmid" is null, a VMID will be generated on the

     * server (for use by the client in subsequent calls) and

     * returned.

     *

     * The client must call the "dirty" method to renew the lease

     * before the "lease" time expires or all references to remote

     * objects in this VM that the client holds are considered

     * "unreferenced".

     */

    public Lease dirty(ObjID[] ids, long sequenceNum, Lease lease) {

        VMID vmid = lease.getVMID();

        /*

         * The server specifies the lease value; the client has

         * no say in the matter.

         */

        long duration = leaseValue;

        if (dgcLog.isLoggable(Log.VERBOSE)) {

            dgcLog.log(Log.VERBOSE, "vmid = " + vmid);

        }

        // create a VMID if one wasn't supplied

        if (vmid == null) {

            vmid = new VMID();

            if (dgcLog.isLoggable(Log.BRIEF)) {

                String clientHost;

                try {

                    clientHost = RemoteServer.getClientHost();

                } catch (ServerNotActiveException e) {

                    clientHost = "<unknown host>";

                }

                dgcLog.log(Log.BRIEF, " assigning vmid " + vmid +

                           " to client " + clientHost);

            }

        }

        lease = new Lease(vmid, duration);

        // record lease information

        synchronized (leaseTable) {

            LeaseInfo info = leaseTable.get(vmid);

            if (info == null) {

                leaseTable.put(vmid, new LeaseInfo(vmid, duration));

                if (checker == null) {

                    checker = scheduler.scheduleWithFixedDelay(

                        new Runnable() {

                            public void run() {

                                checkLeases();

                            }

                        },

                        leaseCheckInterval,

                        leaseCheckInterval, TimeUnit.MILLISECONDS);

                }

            } else {

                info.renew(duration);

            }

        }

        for (ObjID id : ids) {

            if (dgcLog.isLoggable(Log.VERBOSE)) {

                dgcLog.log(Log.VERBOSE, "id = " + id +

                           ", vmid = " + vmid + ", duration = " + duration);

            }

            ObjectTable.referenced(id, sequenceNum, vmid);

        }

        // return the VMID used

        return lease;

    }

    /**

     * The clean call removes the VMID from the set of clients

     * that hold references to the object associated with the LiveRef

     * ref.  The sequence number is used to detect late clean calls.  If the

     * argument "strong" is true, then the clean call is a result of a

     * failed "dirty" call, thus the sequence number for the VMID needs

     * to be remembered until the client goes away.

     */

    public void clean(ObjID[] ids, long sequenceNum, VMID vmid, boolean strong)

    {

        for (ObjID id : ids) {

            if (dgcLog.isLoggable(Log.VERBOSE)) {

                dgcLog.log(Log.VERBOSE, "id = " + id +

                    ", vmid = " + vmid + ", strong = " + strong);

            }

            ObjectTable.unreferenced(id, sequenceNum, vmid, strong);

        }

    }

    /**

     * Register interest in receiving a callback when this VMID

     * becomes inaccessible.

     */

    void registerTarget(VMID vmid, Target target) {

        synchronized (leaseTable) {

            LeaseInfo info = leaseTable.get(vmid);

            if (info == null) {

                target.vmidDead(vmid);

            } else {

                info.notifySet.add(target);

            }

        }

    }

    /**

     * Remove notification request.

     */

    void unregisterTarget(VMID vmid, Target target) {

        synchronized (leaseTable) {

            LeaseInfo info = leaseTable.get(vmid);

            if (info != null) {

                info.notifySet.remove(target);

            }

        }

    }

    /**

     * Check if leases have expired.  If a lease has expired, remove

     * it from the table and notify all interested parties that the

     * VMID is essentially "dead".

     *

     * @return if true, there are leases outstanding; otherwise leases

     * no longer need to be checked

     */

    private void checkLeases() {

        long time = System.currentTimeMillis();

        /* List of vmids that need to be removed from the leaseTable */

        List<LeaseInfo> toUnregister = new ArrayList<>();

        /* Build a list of leaseInfo objects that need to have

         * targets removed from their notifySet.  Remove expired

         * leases from leaseTable.

         */

        synchronized (leaseTable) {

            Iterator<LeaseInfo> iter = leaseTable.values().iterator();

            while (iter.hasNext()) {

                LeaseInfo info = iter.next();

                if (info.expired(time)) {

                    toUnregister.add(info);

                    iter.remove();

                }

            }

            if (leaseTable.isEmpty()) {

                checker.cancel(false);

                checker = null;

            }

        }

        /* Notify and unegister targets without holding the lock on

         * the leaseTable so we avoid deadlock.

         */

        for (LeaseInfo info : toUnregister) {

            for (Target target : info.notifySet) {

                target.vmidDead(info.vmid);

            }

        }

    }

    static {

        /*

         * "Export" the singleton DGCImpl in a context isolated from

         * the arbitrary current thread context.

         */

        AccessController.doPrivileged(new PrivilegedAction<Void>() {

            public Void run() {

                ClassLoader savedCcl =

                    Thread.currentThread().getContextClassLoader();

                try {

                    Thread.currentThread().setContextClassLoader(

                        ClassLoader.getSystemClassLoader());

                    /*

                     * Put remote collector object in table by hand to prevent

                     * listen on port.  (UnicastServerRef.exportObject would

                     * cause transport to listen.)

                     */

                    try {

                        dgc = new DGCImpl();

                        ObjID dgcID = new ObjID(ObjID.DGC_ID);

                        LiveRef ref = new LiveRef(dgcID, 0);

                        UnicastServerRef disp = new UnicastServerRef(ref);

                        Remote stub =

                            Util.createProxy(DGCImpl.class,

                                             new UnicastRef(ref), true);

                        disp.setSkeleton(dgc);

                        Target target =

                            new Target(dgc, disp, stub, dgcID, true);

                        ObjectTable.putTarget(target);

                    } catch (RemoteException e) {

                        throw new Error(

                            "exception initializing server-side DGC", e);

                    }

                } finally {

                    Thread.currentThread().setContextClassLoader(savedCcl);

                }

                return null;

            }

        });

    }

    private static class LeaseInfo {

        VMID vmid;

        long expiration;

        Set<Target> notifySet = new HashSet<>();

        LeaseInfo(VMID vmid, long lease) {

            this.vmid = vmid;

            expiration = System.currentTimeMillis() + lease;

        }

        synchronized void renew(long lease) {

            long newExpiration = System.currentTimeMillis() + lease;

            if (newExpiration > expiration)

                expiration = newExpiration;

        }

        boolean expired(long time) {

            if (expiration < time) {

                if (dgcLog.isLoggable(Log.BRIEF)) {

                    dgcLog.log(Log.BRIEF, vmid.toString());

                }

                return true;

            } else {

                return false;

            }

        }

    }

}