Examples of org.jgroups.protocols.CENTRAL_LOCK

org.jgroups.protocols.CENTRAL_LOCK
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.
An alternative is also the {@link org.jgroups.protocols.PEER_LOCK} protocol. @author Bela Ban @since 2.12 @see Locking @see PEER_LOCK

        System.out.println("[" + Thread.currentThread().getId() + "] signalled " + name);
    }


    protected void addLockingProtocol(JChannel ch) {
        ProtocolStack stack=ch.getProtocolStack();
        Protocol lockprot = new CENTRAL_LOCK();
        lockprot.setLevel("trace");
        stack.insertProtocolAtTop(lockprot);
    }

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                ProtocolStack protocolStack = channel.getProtocolStack();
                Protocol centralLock = protocolStack.findProtocol(CENTRAL_LOCK.class);
                if (centralLock == null) {
                    // add the locking protocol
                    CENTRAL_LOCK lockingProtocol = new CENTRAL_LOCK();
                    // we have to call init because the channel has already been created
                    lockingProtocol.init();
                    protocolStack.addProtocol(lockingProtocol);
                }
                this.lockService = new LockService(this.channel);


                // Add a listener through which we'll know what's going on within the cluster ...

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                boolean alreadyHasForkProtocol = mainChannel.getProtocolStack().findProtocol(FORK.class) != null;


                // add the fork at the top of the stack to preserve the default configuration
                // and use the name of the cluster as the stack id
                this.channel = new ForkChannel(mainChannel, forkStackId, FORK_CHANNEL_NAME, true, ProtocolStack.ABOVE,
                                               topProtocol.getClass(), new CENTRAL_LOCK());


                // always add central lock to the stack
                this.lockService = new LockService(this.channel);


                // Add a listener through which we'll know what's going on within the cluster ...

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public class LockServiceConcurrencyTest extends BMNGRunner {
    protected JChannel    ch;
    protected LockService lock_service;


    @BeforeMethod protected void init() throws Exception {
        ch=new JChannel(Util.getTestStack(new CENTRAL_LOCK())).name("A");
        lock_service=new LockService(ch);
        ch.connect("LockServiceConcurrencyTest");
    }

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    }






    protected JChannel createChannel(String name) throws Exception {
        Protocol[] stack=Util.getTestStack(new CENTRAL_LOCK().level("trace"));
        return new JChannel(stack).name(name);
    }

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