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package sun.rmi.transport;
import java.rmi.server.UID;
import java.security.AccessController;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.Future;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import sun.rmi.runtime.RuntimeUtil;
import sun.security.action.GetLongAction;
Holds strong references to a set of remote objects, or live remote
references to remote objects, after they have been marshalled (as
remote references) as parts of the arguments or the result of a
remote invocation. The purpose is to prevent remote objects or
live remote references that might otherwise be determined to be
unreachable in this VM from being locally garbage collected before
the receiver has had an opportunity to register the unmarshalled
remote references for DGC.
The references are held strongly until an acknowledgment has been
received that the receiver has had an opportunity to process the
remote references or until a timeout has expired. For remote
references sent as parts of the arguments of a remote invocation,
the acknowledgment is the beginning of the response indicating
completion of the remote invocation. For remote references sent as
parts of the result of a remote invocation, a UID is included as
part of the result, and the acknowledgment is a transport-level
"DGCAck" message containing that UID.
Author: Ann Wollrath, Peter Jones
/**
* Holds strong references to a set of remote objects, or live remote
* references to remote objects, after they have been marshalled (as
* remote references) as parts of the arguments or the result of a
* remote invocation. The purpose is to prevent remote objects or
* live remote references that might otherwise be determined to be
* unreachable in this VM from being locally garbage collected before
* the receiver has had an opportunity to register the unmarshalled
* remote references for DGC.
*
* The references are held strongly until an acknowledgment has been
* received that the receiver has had an opportunity to process the
* remote references or until a timeout has expired. For remote
* references sent as parts of the arguments of a remote invocation,
* the acknowledgment is the beginning of the response indicating
* completion of the remote invocation. For remote references sent as
* parts of the result of a remote invocation, a UID is included as
* part of the result, and the acknowledgment is a transport-level
* "DGCAck" message containing that UID.
*
* @author Ann Wollrath
* @author Peter Jones
**/
public class DGCAckHandler {
timeout for holding references without receiving an acknowledgment /** timeout for holding references without receiving an acknowledgment */
private static final long dgcAckTimeout = // default 5 minutes
AccessController.doPrivileged(
new GetLongAction("sun.rmi.dgc.ackTimeout", 300000));
thread pool for scheduling delayed tasks /** thread pool for scheduling delayed tasks */
private static final ScheduledExecutorService scheduler =
AccessController.doPrivileged(
new RuntimeUtil.GetInstanceAction()).getScheduler();
table mapping ack ID to handler /** table mapping ack ID to handler */
private static final Map<UID,DGCAckHandler> idTable =
Collections.synchronizedMap(new HashMap<UID,DGCAckHandler>());
private final UID id;
private List<Object> objList = new ArrayList<>(); // null if released
private Future<?> task = null;
Creates a new DGCAckHandler, associated with the specified UID
if the argument is not null.
References added to this DGCAckHandler will be held strongly
until its "release" method is invoked or (after the
"startTimer" method has been invoked) the timeout has expired.
If the argument is not null, then invoking the static
"received" method with the specified UID is equivalent to
invoking this instance's "release" method.
/**
* Creates a new DGCAckHandler, associated with the specified UID
* if the argument is not null.
*
* References added to this DGCAckHandler will be held strongly
* until its "release" method is invoked or (after the
* "startTimer" method has been invoked) the timeout has expired.
* If the argument is not null, then invoking the static
* "received" method with the specified UID is equivalent to
* invoking this instance's "release" method.
**/
DGCAckHandler(UID id) {
this.id = id;
if (id != null) {
assert !idTable.containsKey(id);
idTable.put(id, this);
}
}
Adds the specified reference to this DGCAckHandler.
/**
* Adds the specified reference to this DGCAckHandler.
**/
synchronized void add(Object obj) {
if (objList != null) {
objList.add(obj);
}
}
Starts the timer for this DGCAckHandler. After the timeout has
expired, the references are released even if the acknowledgment
has not been received.
/**
* Starts the timer for this DGCAckHandler. After the timeout has
* expired, the references are released even if the acknowledgment
* has not been received.
**/
synchronized void startTimer() {
if (objList != null && task == null) {
task = scheduler.schedule(new Runnable() {
public void run() {
release();
}
}, dgcAckTimeout, TimeUnit.MILLISECONDS);
}
}
Releases the references held by this DGCAckHandler.
/**
* Releases the references held by this DGCAckHandler.
**/
synchronized void release() {
if (task != null) {
task.cancel(false);
task = null;
}
objList = null;
}
Causes the DGCAckHandler associated with the specified UID to
release its references.
/**
* Causes the DGCAckHandler associated with the specified UID to
* release its references.
**/
public static void received(UID id) {
DGCAckHandler h = idTable.remove(id);
if (h != null) {
h.release();
}
}
}