/*
 * Copyright (c) 2014 Cisco Systems, Inc. and others. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
 * and is available at http://www.eclipse.org/legal/epl-v10.html
 */
package org.opendaylight.mdsal.binding.api;

import org.eclipse.jdt.annotation.NonNull;

/**
 * A factory which allocates new transactions to operate on the data tree.
 *
 * <p>
 * <b>Note:</b> This interface is not intended to be used directly, but rather via subinterfaces
 * which introduces additional semantics to allocated transactions.
 * <ul>
 * <li> {@link DataBroker}
 * <li> {@link TransactionChain}
 * </ul>
 *
 * <p>
 * All operations on the data tree are performed via one of the transactions:
 * <ul>
 * <li>Read-Only - allocated using {@link #newReadOnlyTransaction()}
 * <li>Write-Only - allocated using {@link #newWriteOnlyTransaction()}
 * </ul>
 *
 * <p>
 * These transactions provides a stable isolated view of the data tree, which is guaranteed to be
 * not affected by other concurrent transactions, until transaction is committed.
 *
 * <p>
 * For a detailed explanation of how transaction are isolated and how transaction-local changes are
 * committed to global data tree, see {@link ReadTransaction}, {@link WriteTransaction}
 * and {@link WriteTransaction#commit()}.
 *
 * <p>
 * It is strongly recommended to use the type of transaction, which provides only the minimal
 * capabilities you need. This allows for optimizations at the data broker / data store level. For
 * example, implementations may optimize the transaction for reading if they know ahead of time that
 * you only need to read data - such as not keeping additional meta-data, which may be required for
 * write transactions.
 *
 * <p>
 * <b>Implementation Note:</b> This interface is not intended to be implemented by users of MD-SAL,
 * but only to be consumed by them.
 *
 * @see DataBroker
*/
public interface TransactionFactory {
    /**
     * Allocates a new read-only transaction which provides an immutable snapshot of the data tree. The view of data
     * tree is an immutable snapshot of current data tree state when transaction was allocated.
     *
     * @return A new read-only transaction
     */
    @NonNull ReadTransaction newReadOnlyTransaction();

    /**
     * Allocates new read-write transaction which provides a mutable view of the data tree.
     *
     * <p>
     * Preconditions for mutation of data tree are captured from the snapshot of data tree state, when the transaction
     * is allocated. If data was changed during transaction in an incompatible way then the commit of this transaction
     * will fail. See {@link ReadWriteTransaction#commit()} for more details about conflicting and non-conflicting
     * changes and failure scenarios.
     *
     * @return new read-write transaction
     */
    @NonNull ReadWriteTransaction newReadWriteTransaction();

    /**
     * Allocates new write-only transaction based on latest state of data tree.
     *
     * <p>
     * Preconditions for mutation of data tree are captured from the snapshot of data tree state, when the transaction
     * is allocated. If data was changed during transaction in an incompatible way then the commit of this transaction
     * will fail. See {@link WriteTransaction#commit()} for more details about conflicting and not-conflicting changes
     * and failure scenarios.
     *
     * <p>
     * Since this transaction does not provide a view of the data it SHOULD BE used only by callers who are exclusive
     * writers (exporters of data) to the subtree they modify. This prevents optimistic lock failures as described in
     * {@link WriteTransaction#commit()}.
     *
     * <p>
     * Exclusivity of writers to particular subtree SHOULD BE enforced by external locking mechanism.
     *
     * @return new write-only transaction
     */
    @NonNull WriteTransaction newWriteOnlyTransaction();
}