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Micro Distribution of the Payara Project
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package org.jvnet.hk2.config;
import java.beans.PropertyChangeEvent;
import java.lang.reflect.Proxy;
import java.util.LinkedList;
import java.util.List;
/**
* Simple transaction mechanism for config-api objects
*
* @author Jerome Dochez
*/
public class Transaction {
final LinkedList participants = new LinkedList();
/**
* Enlists a new participant in this transaction
*
* @param t new participant to this transaction
*
*/
synchronized void addParticipant(Transactor t) {
// add participants first so the lastly created elements are processed before the parent
// is modified, this is especially important when sub elements have key attributes the parent
// need (or the habitat).
participants.addFirst(t);
}
/**
* Rollbacks all participants to this transaction.
*/
public synchronized void rollback() {
for (Transactor t : participants) {
t.abort(this);
}
}
/**
* Tests if the transaction participants will pass the prepare phase successfully.
* The prepare phase will invoke validation of the changes, so a positive return
* usually means the changes are valid and unless a external factor arise, the
* {@link #commit()} method will succeed.
*
* @return true if the participants changes are valid, false otherwise
* @throws TransactionFailure if the changes are not valid
*/
public boolean canCommit() throws TransactionFailure {
for (Transactor t : participants) {
if (!t.canCommit(this)) {
return false;
}
}
return true;
}
/**
* Commits all participants to this transaction
*
* @return list of PropertyChangeEvent for the changes that were applied to the
* participants during the transaction.
* @throws RetryableException if the transaction cannot commit at this time but
* could succeed later.
* @throws TransactionFailure if the transaction commit failed.
*/
public synchronized List commit()
throws RetryableException, TransactionFailure {
if (!canCommit()) {
throw new RetryableException();
}
LinkedList transactionChanges = new LinkedList();
for (Transactor t : participants) {
for (PropertyChangeEvent evt : t.commit(this)) {
// adding the last committed changes last to reverse the list of participants
// as participants are always added first, we want the events to be consistent
// with the transactional code meaning FIFO (first element modified/created generates
// first events).
transactionChanges.addFirst(evt);
}
}
// any ConfigBean in our transactor should result in sending transaction events, but only once.
for (Transactor t : participants) {
if (t instanceof WriteableView) {
((WriteableView) t).getMasterView().getHabitat().getService(Transactions.class).addTransaction(transactionChanges);
break;
}
}
return transactionChanges;
}
/**
* Returns the transaction associated with a writable view
* @param source the proxy to the writable view
* @return the transaction object for that view or null if not transaction is in progress
*/
public static Transaction getTransaction(final T source) {
Object sourceBean = Proxy.getInvocationHandler(source);
if (sourceBean instanceof WriteableView) {
return ((WriteableView) sourceBean).getTransaction();
}
return null;
}
/**
* Enroll a configuration object in a transaction and returns a writeable view of it
*
* @param source the configured interface implementation
* @return the new interface implementation providing write access
* @throws TransactionFailure if the object cannot be enrolled (probably already enrolled in
* another transaction).
*/
public T enroll(final T source)
throws TransactionFailure {
T configBeanProxy = ConfigSupport.revealProxy(source);
ConfigView sourceBean = (ConfigView) Proxy.getInvocationHandler(configBeanProxy);
WriteableView writeableView = ConfigSupport.getWriteableView(configBeanProxy, (ConfigBean) sourceBean.getMasterView());
if (!writeableView.join(this)) {
throw new TransactionFailure("Cannot join transaction : " + sourceBean.getProxyType());
}
return (T) writeableView.getProxy(sourceBean.getProxyType());
}
}