The clean call removes the 'vmid' from the reference list of each remote object indicated in 'id's.

  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.
Parameters:
- ids - IDs of objects to mark as unreferenced by calling client
- sequenceNum - sequence number
- vmid - client VMID
- strong - make 'strong' clean call
Throws:
- RemoteException - if clean call fails

  The dirty call requests leases for the remote object references associated with the object identifiers contained in the array 'ids'.

  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.
Returns: granted lease
Parameters:
- ids - IDs of objects to mark as referenced by calling client
- sequenceNum - sequence number
- lease - requested lease
Throws:
- RemoteException - if dirty call fails