org.jgroups.protocols.CENTRAL_LOCK Maven / Gradle / Ivy
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This artifact provides a single jar that contains all classes required to use remote EJB and JMS, including
all dependencies. It is intended for use by those not using maven, maven users should just import the EJB and
JMS BOM's instead (shaded JAR's cause lots of problems with maven, as it is very easy to inadvertently end up
with different versions on classes on the class path).
package org.jgroups.protocols;
import org.jgroups.Address;
import org.jgroups.View;
import org.jgroups.annotations.ManagedAttribute;
import org.jgroups.annotations.Property;
import org.jgroups.blocks.locking.LockNotification;
import org.jgroups.util.Owner;
import org.jgroups.util.Util;
import java.util.*;
/**
* Implementation of a locking protocol which acquires locks by contacting the coordinator. Because the
* coordinator maintains all locks, no total order configuration is required.
* CENTRAL_LOCK has all members send lock and unlock requests to a central coordinator. The coordinator has a queue for
* incoming requests, and grants locks based on order of arrival. To prevent all acquired locks from being forgotten
* when the coordinator crashes, setting num_backups lets the coordinator backup lock information to a number of
* backup nodes. Valid values for num_backups are 0 (no backup) to N-1, e.g. in a cluster of 4, we can have only 3 backup
* nodes.
* Say we have a cluster of {A,B,C,D,E} and num_backups=1. A is the coordinator, and A updates all locks (and released
* locks) in B as well. When A crashes, everybody falls over to B for sending lock and unlock requests.
* B in turn copies all existing locks over to C and - when locks are acquired or released - forwards this
* information to C as well.
* @author Bela Ban
* @since 2.12
* @see Locking
* @deprecated See http://belaban.blogspot.com/2020/11/i-hate-distributed-locks.html.
*/
@Deprecated
public class CENTRAL_LOCK extends Locking implements LockNotification {
@Property(description="Number of backups to the coordinator. Server locks get replicated to these nodes as well")
protected int num_backups=1;
protected Address coord;
@ManagedAttribute
protected boolean is_coord;
protected final List backups=new ArrayList<>();
public CENTRAL_LOCK() {
super();
addLockListener(this);
}
protected Owner getOwner() {
return use_thread_id_for_lock_owner? super.getOwner(): new Owner(local_addr, -1);
}
public Address getCoord() {
return coord;
}
public boolean isCoord() {
return is_coord;
}
@ManagedAttribute
public String getCoordinator() {
return coord != null? coord.toString() : "n/a";
}
public int getNumberOfBackups() {
return num_backups;
}
public CENTRAL_LOCK setNumberOfBackups(int num_backups) {
this.num_backups=num_backups; return this;
}
@ManagedAttribute
public String getBackups() {
return backups != null? backups.toString() : null;
}
protected void sendGrantLockRequest(String lock_name, int lock_id, Owner owner, long timeout, boolean is_trylock) {
Address dest=coord;
if(dest == null)
throw new IllegalStateException("No coordinator available, cannot send GRANT-LOCK request");
sendRequest(dest, Type.GRANT_LOCK, lock_name, lock_id, owner, timeout, is_trylock);
}
protected void sendReleaseLockRequest(String lock_name, int lock_id, Owner owner) {
Address dest=coord;
if(dest == null)
throw new IllegalStateException("No coordinator available, cannot send RELEASE-LOCK request");
sendRequest(dest, Type.RELEASE_LOCK, lock_name, lock_id, owner, 0, false);
}
protected void sendCreateLockRequest(Address dest, String lock_name, Owner owner) {
sendRequest(dest, Type.CREATE_LOCK, lock_name, owner, 0, false);
}
protected void sendDeleteLockRequest(Address dest, String lock_name) {
sendRequest(dest, Type.DELETE_LOCK, lock_name, null, 0, false);
}
@Override
protected void sendAwaitConditionRequest(String lock_name, Owner owner) {
sendRequest(coord, Type.LOCK_AWAIT, lock_name, owner, 0, false);
}
@Override
protected void sendSignalConditionRequest(String lock_name, boolean all) {
sendRequest(coord, all ? Type.COND_SIG_ALL : Type.COND_SIG, lock_name, null, 0, false);
}
@Override
protected void sendDeleteAwaitConditionRequest(String lock_name, Owner owner) {
sendRequest(coord, Type.DELETE_LOCK_AWAIT, lock_name, owner, 0, false);
}
public void handleView(View view) {
super.handleView(view);
Address old_coord=coord;
if(view.size() > 0) {
coord=view.getCoord();
is_coord=coord.equals(local_addr);
log.debug("[%s] coord=%s, is_coord=%b", local_addr, coord, is_coord);
}
if(is_coord && num_backups > 0) {
List new_backups=Util.pickNext(view.getMembers(), local_addr, num_backups);
List copy_locks_list=null;
synchronized(backups) {
if(!backups.equals(new_backups)) {
copy_locks_list=new ArrayList<>(new_backups);
copy_locks_list.removeAll(backups);
backups.clear();
backups.addAll(new_backups);
}
}
if(copy_locks_list != null && !copy_locks_list.isEmpty())
copyLocksTo(copy_locks_list);
}
// For all non-acquired client locks, send the GRANT_LOCK request to the new coordinator (if changed)
if(old_coord != null && !old_coord.equals(coord))
client_lock_table.resendPendingLockRequests();
}
public void lockCreated(String name) {
}
public void lockDeleted(String name) {
}
public void locked(String lock_name, Owner owner) {
if(is_coord)
updateBackups(Type.CREATE_LOCK, lock_name, owner);
}
public void unlocked(String lock_name, Owner owner) {
if(is_coord)
updateBackups(Type.DELETE_LOCK, lock_name, owner);
}
public void lockRevoked(String lock_name, Owner current_owner) {
log.warn("%s: lock %s has been revoked; the existing owner is %s", local_addr, lock_name, current_owner);
}
public void awaiting(String lock_name, Owner owner) {
if(is_coord)
updateBackups(Type.CREATE_AWAITER, lock_name, owner);
}
public void awaited(String lock_name, Owner owner) {
if(is_coord)
updateBackups(Type.DELETE_AWAITER, lock_name, owner);
}
protected void updateBackups(Type type, String lock_name, Owner owner) {
synchronized(backups) {
for(Address backup: backups)
sendRequest(backup, type, lock_name, owner, 0, false);
}
}
protected void copyLocksTo(List new_joiners) {
Map copy;
synchronized(server_locks) {
copy=new HashMap<>(server_locks);
}
log.trace("[%s] copying locks to %s", local_addr, new_joiners);
for(Map.Entry entry: copy.entrySet()) {
for(Address joiner: new_joiners) {
ServerLock lock = entry.getValue();
if (lock.owner != null) {
sendCreateLockRequest(joiner, entry.getKey(), entry.getValue().owner);
}
synchronized (lock.condition) {
Queue queue = lock.condition.queue;
for (Owner owner : queue) {
sendAwaitConditionRequest(lock.lock_name, owner);
}
}
}
}
}
}