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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 * 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).

 *

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 * 2 along with this work; if not, write to the Free Software Foundation,

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package java.rmi.dgc;

import java.rmi.*;

import java.rmi.server.ObjID;

/**

 * The DGC abstraction is used for the server side of the distributed

 * garbage collection algorithm. This interface contains the two

 * methods: dirty and clean. A dirty call is made when a remote

 * reference is unmarshaled in a client (the client is indicated by

 * its VMID). A corresponding clean call is made when no more

 * references to the remote reference exist in the client. A failed

 * dirty call must schedule a strong clean call so that the call's

 * sequence number can be retained in order to detect future calls

 * received out of order by the distributed garbage collector.

 *

 * A reference to a remote object is leased for a period of time by

 * the client holding the reference. The lease period starts when the

 * dirty call is received. It is the client's responsibility to renew

 * the leases, by making additional dirty calls, on the remote

 * references it holds before such leases expire. If the client does

 * not renew the lease before it expires, the distributed garbage

 * collector assumes that the remote object is no longer referenced by

 * that client.

 *

 * @author Ann Wollrath

 */

public interface DGC extends Remote {

    /**

     * The dirty call requests leases for the remote object references

     * associated with the object identifiers contained in the array

     * 'ids'. The 'lease' contains a client's unique VM identifier (VMID)

     * and a requested lease period. For each remote object exported

     * in the local VM, the garbage collector maintains a reference

     * list-a list of clients that hold references to it. If the lease

     * is granted, the garbage collector adds the client's VMID to the

     * reference list for each remote object indicated in 'ids'. The

     * 'sequenceNum' parameter is a sequence number that is used to

     * detect and discard late calls to the garbage collector. The

     * sequence number should always increase for each subsequent call

     * to the garbage collector.

     *

     * Some clients are unable to generate a VMID, since a VMID is a

     * universally unique identifier that contains a host address

     * which some clients are unable to obtain due to security

     * restrictions. In this case, a client can use a VMID of null,

     * and the distributed garbage collector will assign a VMID for

     * the client.

     *

     * The dirty call returns a Lease object that contains the VMID

     * used and the lease period granted for the remote references (a

     * server may decide to grant a smaller lease period than the

     * client requests). A client must use the VMID the garbage

     * collector uses in order to make corresponding clean calls when

     * the client drops remote object references.

     *

     * A client VM need only make one initial dirty call for each

     * remote reference referenced in the VM (even if it has multiple

     * references to the same remote object). The client must also

     * make a dirty call to renew leases on remote references before

     * such leases expire. When the client no longer has any

     * references to a specific remote object, it must schedule a

     * clean call for the object ID associated with the reference.

     *

     * @param ids IDs of objects to mark as referenced by calling client

     * @param sequenceNum sequence number

     * @param lease requested lease

     * @return granted lease

     * @throws RemoteException if dirty call fails

     */

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

        throws RemoteException;

    /**

     * The clean call removes the 'vmid' from the reference list of

     * each remote object indicated in 'id's.  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 client 'vmid' needs to be

     * remembered.

     *

     * @param ids IDs of objects to mark as unreferenced by calling client

     * @param sequenceNum sequence number

     * @param vmid client VMID

     * @param strong make 'strong' clean call

     * @throws RemoteException if clean call fails

     */

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

        throws RemoteException;

}