io.permazen.core.SnapshotTransaction Maven / Gradle / Ivy
/*
* Copyright (C) 2015 Archie L. Cobbs. All rights reserved.
*/
package io.permazen.core;
import io.permazen.kv.KVStore;
/**
* A "snapshot" {@link Transaction} that persists indefinitely.
*
*
* {@link SnapshotTransaction}s hold a "snapshot" of some portion of the state of a {@link Transaction}
* for later use. Each {@link SnapshotTransaction} contains its own set of "snapshot" objects.
*
*
* {@link SnapshotTransaction}s can never be closed (i.e., committed or rolled-back); they persist in memory until
* no longer referenced. {@link Transaction.Callback}s may be registered but they will never be invoked.
*
*
* {@link SnapshotTransaction}s can be based on an arbitrary {@link KVStore};
* see {@link Database#createSnapshotTransaction Database.createSnapshotTransaction()}.
*
* @see Transaction#createSnapshotTransaction Transaction.createSnapshotTransaction()
* @see Database#createSnapshotTransaction Database.createSnapshotTransaction()
* @see io.permazen.SnapshotJTransaction
*/
public class SnapshotTransaction extends Transaction {
// Constructors
SnapshotTransaction(Database db, KVStore kvstore, Schemas schemas) {
super(db, new SnapshotKVTransaction(kvstore), schemas);
}
SnapshotTransaction(Database db, KVStore kvstore, Schemas schemas, int versionNumber) {
super(db, new SnapshotKVTransaction(kvstore), schemas, versionNumber);
}
SnapshotTransaction(Database db, KVStore kvstore, Schemas schemas, Schema schema) {
super(db, new SnapshotKVTransaction(kvstore), schemas, schema);
}
// Methods
@Override
public boolean isSnapshot() {
return true;
}
/**
* Get the underlying {@link KVStore} that holds this snapshot transaction's state.
*
* @return underlying {@link KVStore}
*/
public KVStore getKVStore() {
return ((SnapshotKVTransaction)this.kvt).delegate();
}
/**
* Delete all objects contained in this snapshot transaction.
*
*
* Upon return, the underlying key/value store will still contain meta-data, but no objects.
*/
public synchronized void reset() {
if (this.stale)
throw new StaleTransactionException(this);
Layout.deleteObjectData(this.kvt);
}
/**
* Commit this transaction.
*
*
* {@link SnapshotTransaction}s do not support this method and will always throw {@link UnsupportedOperationException}.
*
* @throws UnsupportedOperationException always
*/
@Override
public void commit() {
throw new UnsupportedOperationException("snapshot transaction");
}
/**
* Roll back this transaction.
*
*
* {@link SnapshotTransaction}s do not support this method and will always throw {@link UnsupportedOperationException}.
*
* @throws UnsupportedOperationException always
*/
@Override
public void rollback() {
throw new UnsupportedOperationException("snapshot transaction");
}
/**
* Register a transaction callback to be invoked when this transaction completes.
*
*
* {@link Transaction.Callback}s registered with a {@link SnapshotTransaction} will by definition never be invoked.
* Therefore, this method simply discards {@code callback}.
*/
@Override
public void addCallback(Callback callback) {
}
/**
* Determine whether this transaction is still valid.
*
*
* {@link SnapshotTransaction}s are always valid.
*
* @return true always
*/
@Override
public boolean isValid() {
return super.isValid();
}
}