org.apache.jackrabbit.spi.commons.lock
Class Locked

java.lang.Object
  org.apache.jackrabbit.spi.commons.lock.Locked

public abstract class Locked
extends Object

Locked is a utility to synchronize modifications on a lockable node. The modification is applied while the lock on the node is held, thus ensuring that the modification will never fail with an InvalidItemStateException. This utility can be used with any JCR Repository, not just Jackrabbit.

The following example shows how this utility can be used to implement a persistent counter:

 Node counter = ...;
 long nextValue = ((Long) new Locked() {
     protected Object run(Node counter) throws RepositoryException {
         Property seqProp = counter.getProperty("value");
         long value = seqProp.getLong();
         seqProp.setValue(++value);
         seqProp.save();
         return new Long(value);
     }
 }.with(counter, false)).longValue();
 

If you specify a timeout you need to check the return value whether the run method could be executed within the timeout period:

 Node counter = ...;
 Object ret = new Locked() {
     protected Object run(Node counter) throws RepositoryException {
         Property seqProp = counter.getProperty("value");
         long value = seqProp.getLong();
         seqProp.setValue(++value);
         seqProp.save();
         return new Long(value);
     }
 }.with(counter, false);
 if (ret == Locked.TIMED_OUT) {
     // do whatever you think is appropriate in this case
 } else {
     // get the value
     long nextValue = ((Long) ret).longValue();
 }
 

Field Summary

static Object

TIMED_OUT Object returned when timeout is reached without being able to call run(javax.jcr.Node) while holding the lock.

Constructor Summary

Locked()

Method Summary

protected abstract Object	run(Node node) This method is executed while holding the lock.
Object	with(Node lockable, boolean isDeep) Executes run(javax.jcr.Node) while the lock on lockable is held.
Object	with(Node lockable, boolean isDeep, long timeout) Executes the method run(javax.jcr.Node) within the scope of a lock held on lockable.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

TIMED_OUT

public static final Object TIMED_OUT

Object returned when timeout is reached without being able to call run(javax.jcr.Node) while holding the lock.

Constructor Detail

Locked

public Locked()

Method Detail

with

public Object with(Node lockable,
                   boolean isDeep)
            throws RepositoryException,
                   InterruptedException

Executes run(javax.jcr.Node) while the lock on lockable is held. This method will block until run(javax.jcr.Node) is executed while holding the lock on node lockable.

Parameters:

lockable - a lockable node.

isDeep - true if lockable will be locked deep.

Returns:

the object returned by run(javax.jcr.Node).

Throws:

IllegalArgumentException - if lockable is not mix:lockable.

RepositoryException - if run(javax.jcr.Node) throws an exception.

InterruptedException - if this thread is interrupted while waiting for the lock on node lockable.

with

public Object with(Node lockable,
                   boolean isDeep,
                   long timeout)
            throws UnsupportedRepositoryOperationException,
                   RepositoryException,
                   InterruptedException

Executes the method run(javax.jcr.Node) within the scope of a lock held on lockable.

Parameters:

lockable - the node where the lock is obtained from.

isDeep - true if lockable will be locked deep.

timeout - time in milliseconds to wait at most to aquire the lock.

Returns:

the object returned by run(javax.jcr.Node) or TIMED_OUT if the lock on lockable could not be aquired within the specified timeout.

Throws:

IllegalArgumentException - if timeout is negative or lockable is not mix:lockable.

RepositoryException - if run(javax.jcr.Node) throws an exception.

UnsupportedRepositoryOperationException - if this repository does not support locking.

InterruptedException - if this thread is interrupted while waiting for the lock on node lockable.

run

protected abstract Object run(Node node)
                       throws RepositoryException

This method is executed while holding the lock.

Parameters:

node - The Node on which the lock is placed.

Returns:

an object which is then returned by with().

Throws:

RepositoryException - if an error occurs.