496 lines
20 KiB
C++
496 lines
20 KiB
C++
/*
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* LMDB Abstraction Layer.
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* Copyright (C) 2023 Yury Gubich <blue@macaw.me>
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef LMDBAL_CURSOR_HPP
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#define LMDBAL_CURSOR_HPP
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#include "cursor.h"
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/**
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* \class LMDBAL::Cursor
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* \brief An object to iterate storages.
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*
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* \tparam K type of the keys in the storage that this cursor would iterate
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* \tparam V type of the values in the storage that this cursor would iterate
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*
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* Cursor allowes you to perform sequential querries, navigate from one element to another at reduced operation price.
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* For now Cursors are read only but in the future you might also be able to write to the storage with them.
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*
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* Cursors are owned by the storage, they die with the storage.
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* They also get closed if the storage is closed (if you close by the database for example)
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*
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* You can obtain an instance of this class calling LMDBAL::Storage::createCursor()
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* and destory it calling LMDBAL::Storage::destoryCursor() at any time, LMDBAL::Base doesn't necessarily need to be opened.
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*
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* You are not supposed to instantiate or destory instances of this class yourself!
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*/
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/**
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* \brief Creates a cursor
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*
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* \param[in] parent a storage that created this cursor
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*/
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template<class K, class V>
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LMDBAL::Cursor<K, V>::Cursor(Storage<K, V>* parent):
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storage(parent),
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cursor(nullptr),
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state(closed)
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{}
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/**
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* \brief Destroys a cursor
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*
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* If the cursor wasn't properly closed - it's going to be upon destruction
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*/
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template<class K, class V>
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LMDBAL::Cursor<K, V>::~Cursor () {
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close();
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}
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/**
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* \brief A private function the storage owning this cursor will call to inform this cursor that the thansaction needs to be aborted
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*/
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template<class K, class V>
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void LMDBAL::Cursor<K, V>::terminated () const {
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close(); //for now it's the same, but if I ever going to make writable cursor - here is where it's gonna be different
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}
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/**
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* \brief Opens the cursor for operations.
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*
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* This is a normal way to start the sequence of operations with the cursor.
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* This variant of the function creates a read only transaction just for this cursor
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*
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* This function should be called when the LMDBAL::Storage is already opened and before any query with this cursor!
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* It will do nothing to a cursor that was already opened (no matter what way).
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*
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* \throws LMDBAL::Closed thrown if you try to open the cursor on a closed database
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* \throws LMDBAL::Unknown thrown if there was a problem opening the cursor by the lmdb, or to begin a transaction
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*/
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template<class K, class V>
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void LMDBAL::Cursor<K, V>::open () const {
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storage->ensureOpened(openCursorMethodName);
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switch (state) {
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case closed: {
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TransactionID txn = storage->beginReadOnlyTransaction();
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int result = mdb_cursor_open(txn, storage->dbi, &cursor);
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if (result != MDB_SUCCESS)
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storage->throwUnknown(result, txn);
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storage->transactionStarted(txn, true);
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state = openedPrivate;
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} break;
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default:
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break;
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}
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}
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/**
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* \brief Opens the cursor for operations.
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*
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* This is a normal way to start the sequence of operations with the cursor.
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* This variant of the function uses for queries a transaction you have obtained somewhere else.
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*
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* This function should be called when the LMDBAL::Storage is already opened and before any query with this cursor!
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* It will do nothing to a cursor that was already opened (no matter what way).
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*
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* \throws LMDBAL::Closed thrown if you try to open the cursor on a closed database
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* \throws LMDBAL::Unknown thrown if there was a problem opening the cursor by the lmdb
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*/
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template<class K, class V>
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void LMDBAL::Cursor<K, V>::open (TransactionID txn) const {
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storage->ensureOpened(openCursorMethodName);
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switch (state) {
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case closed: {
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int result = mdb_cursor_open(txn, storage->dbi, &cursor);
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if (result != MDB_SUCCESS)
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storage->throwUnknown(result);
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state = openedPublic;
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} break;
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default:
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break;
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}
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}
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/**
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* \brief Renews a cursor
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*
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* This function aborts current transaction if the cursor was opened with it's own transaction
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* (does not mess up if the transaction was public),
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* creates new private transaction and rebinds this cursor to it.
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*
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* Theoretically you could call this method if your public transaction was aborted (or commited)
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* but you wish to continue to keep working with your cursor.
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* Or if you just want to rebind your cursor to a new private transaction.
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*
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* This function does nothing if the cursor is closed
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*
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* \param[in] txn a transaction you wish this cursor to be bound to
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*
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* \throws LMDBAL::Closed thrown if you try to renew the cursor on a closed database
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* \throws LMDBAL::Unknown thrown if there was a problem beginning new transaction or if there was a problem renewing the cursor by lmdb
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*/
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template<class K, class V>
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void LMDBAL::Cursor<K, V>::renew () const {
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storage->ensureOpened(renewCursorMethodName);
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switch (state) {
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case openedPrivate: {
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TransactionID txn = mdb_cursor_txn(cursor);
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storage->abortTransaction(txn);
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storage->transactionAborted(txn);
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[[fallthrough]];
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}
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case openedPublic: {
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TransactionID txn = storage->beginReadOnlyTransaction();
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int result = mdb_cursor_renew(txn, cursor);
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if (result != MDB_SUCCESS)
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storage->throwUnknown(result, txn);
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storage->transactionStarted(txn, true);
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state = openedPrivate;
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} break;
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default:
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break;
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}
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}
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/**
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* \brief Renews a cursor
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*
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* This function aborts current transaction if the cursor was opened with it's own transaction
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* (does not mess up if the transaction was public),
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* and rebinds this cursor to a passed new transaction.
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*
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* Theoretically you could call this method if your previous public transaction was aborted (or commited)
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* but you wish to continue to keep working with your cursor.
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* Or if you just want to rebind your cursor to another public transaction.
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*
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* This function does nothing if the cursor is closed
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*
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* \param[in] txn a transaction you wish this cursor to be bound to
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*
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* \throws LMDBAL::Closed thrown if you try to renew the cursor on a closed database
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* \throws LMDBAL::Unknown thrown if there was a problem renewing the cursor by lmdb
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*/
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template<class K, class V>
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void LMDBAL::Cursor<K, V>::renew (TransactionID txn) const {
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storage->ensureOpened(renewCursorMethodName);
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switch (state) {
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case openedPrivate: {
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TransactionID txn = mdb_cursor_txn(cursor);
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storage->abortTransaction(txn);
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storage->transactionAborted(txn);
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[[fallthrough]];
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}
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case openedPublic: {
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int result = mdb_cursor_renew(txn, cursor);
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if (result != MDB_SUCCESS)
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storage->throwUnknown(result);
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state = openedPublic;
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} break;
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default:
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break;
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}
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}
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/**
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* \brief Termiates a sequence of operations with the cursor
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*
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* This is a normal way to tell that you're done with the cursor and don't want to continue the sequence of queries.
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* The state of the cursor is lost after calling this method, some inner resorce is freed.
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*
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* If the cursor was opened with the private transaction - the owner storage will be notified of the aborted transaction.
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*
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* This function does nothing on a closed cursor.
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*/
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template<class K, class V>
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void LMDBAL::Cursor<K, V>::close () const {
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switch (state) {
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case openedPublic: {
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mdb_cursor_close(cursor);
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state = closed;
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} break;
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case openedPrivate: {
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TransactionID txn = mdb_cursor_txn(cursor);
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mdb_cursor_close(cursor);
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storage->abortTransaction(txn);
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storage->transactionAborted(txn);
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state = closed;
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} break;
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default:
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break;
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}
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}
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/**
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* \brief Tells if the cursor is open
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*/
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template<class K, class V>
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bool LMDBAL::Cursor<K, V>::opened () const {
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return state != closed;
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}
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/**
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* \brief Queries the first element in the storage
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*
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* Notifies the storage of the queried element calling LMDBAL::Storage::discoveredRecord()
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*
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* \param[out] key a reference to an object the key of queried element is going to be assigned
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* \param[out] value a reference to an object the value of queried element is going to be assigned
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*
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* \throws LMDBAL::CursorNotReady thrown if you try to call this method on a closed cursor
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* \throws LMDBAL::NotFound thrown if there are no elements in the storage
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* \throws LMDBAL::Unknown thrown if there was some unexpected problem with lmdb
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*/
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template<class K, class V>
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void LMDBAL::Cursor<K, V>::first (K& key, V& value) const {
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operateCursorRead(key, value, MDB_FIRST, firstMethodName, firstOperationName);
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}
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/**
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* \brief Queries the last element in the storage
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*
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* Notifies the storage of the queried element calling LMDBAL::Storage::discoveredRecord()
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*
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* \param[out] key a reference to an object the key of queried element is going to be assigned
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* \param[out] value a reference to an object the value of queried element is going to be assigned
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*
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* \throws LMDBAL::CursorNotReady thrown if you try to call this method on a closed cursor
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* \throws LMDBAL::NotFound thrown if there are no elements in the storage
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* \throws LMDBAL::Unknown thrown if there was some unexpected problem with lmdb
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*/
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template<class K, class V>
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void LMDBAL::Cursor<K, V>::last (K& key, V& value) const {
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operateCursorRead(key, value, MDB_LAST, lastMethodName, lastOperationName);
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}
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/**
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* \brief Queries the next element from the storage
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*
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* If there was no operation before this method positions the cursor on the first element and returns it
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* so, it's basically doing the same as LMDBAL::Cursor::first(K key, V value).
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*
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* It will also throw LMDBAL::NotFound if you call this method being on the last element
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* or if there are no elements in the database.
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*
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* Notifies the storage of the queried element calling LMDBAL::Storage::discoveredRecord()
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*
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* \param[out] key a reference to an object the key of queried element is going to be assigned
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* \param[out] value a reference to an object the value of queried element is going to be assigned
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*
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* \throws LMDBAL::CursorNotReady thrown if you try to call this method on a closed cursor
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* \throws LMDBAL::NotFound thrown if the cursor already was on the last element or if there are no elements in the storage
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* \throws LMDBAL::Unknown thrown if there was some unexpected problem with lmdb
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*/
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template<class K, class V>
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void LMDBAL::Cursor<K, V>::next (K& key, V& value) const {
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operateCursorRead(key, value, MDB_NEXT, nextMethodName, nextOperationName);
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}
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/**
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* \brief Queries the previous element from the storage
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*
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* If there was no operation before this method positions the cursor on the last element and returns it
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* so, it's basically doing the same as LMDBAL::Cursor::last(K key, V value).
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*
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* It will also throw LMDBAL::NotFound if you call this method being on the first element
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* or if there are no elements in the database.
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*
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* Notifies the storage of the queried element calling LMDBAL::Storage::discoveredRecord()
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*
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* \param[out] key a reference to an object the key of queried element is going to be assigned
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* \param[out] value a reference to an object the value of queried element is going to be assigned
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*
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* \throws LMDBAL::CursorNotReady thrown if you try to call this method on a closed cursor
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* \throws LMDBAL::NotFound thrown if the cursor already was on the first element or if there are no elements in the storage
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* \throws LMDBAL::Unknown thrown if there was some unexpected problem with lmdb
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*/
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template<class K, class V>
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void LMDBAL::Cursor<K, V>::prev (K& key, V& value) const {
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operateCursorRead(key, value, MDB_PREV, prevMethodName, prevOperationName);
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}
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/**
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* \brief Returns current cursor element from the storage
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*
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* If there was no operation before this method throws LMDBAL::Unknown for some reason
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*
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* Notifies the storage of the queried element calling LMDBAL::Storage::discoveredRecord()
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*
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* \param[out] key a reference to an object the key of queried element is going to be assigned
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* \param[out] value a reference to an object the value of queried element is going to be assigned
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*
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* \throws LMDBAL::CursorNotReady thrown if you try to call this method on a closed cursor
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* \throws LMDBAL::NotFound probably never thrown but there might be still some corner case I don't know about
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* \throws LMDBAL::Unknown thrown if there was some unexpected problem with lmdb
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*/
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template<class K, class V>
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void LMDBAL::Cursor<K, V>::current (K& key, V& value) const {
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operateCursorRead(key, value, MDB_GET_CURRENT, currentMethodName, currentOperationName);
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}
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/**
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* \brief Queries the first element in the storage
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*
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* Notifies the storage of the queried element calling LMDBAL::Storage::discoveredRecord()
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*
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* \returns std::pair where first is element key and second is element value
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*
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* \throws LMDBAL::CursorNotReady thrown if you try to call this method on a closed cursor
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* \throws LMDBAL::NotFound thrown if there are no elements in the storage
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* \throws LMDBAL::Unknown thrown if there was some unexpected problem with lmdb
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*/
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template<class K, class V>
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std::pair<K, V> LMDBAL::Cursor<K, V>::first () const {
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std::pair<K, V> result;
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operateCursorRead(result.first, result.second, MDB_FIRST, firstMethodName, firstOperationName);
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return result;
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}
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/**
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* \brief Queries the last element in the storage
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*
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* Notifies the storage of the queried element calling LMDBAL::Storage::discoveredRecord()
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*
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* \returns std::pair where first is element key and second is element value
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*
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* \throws LMDBAL::CursorNotReady thrown if you try to call this method on a closed cursor
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* \throws LMDBAL::NotFound thrown if there are no elements in the storage
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* \throws LMDBAL::Unknown thrown if there was some unexpected problem with lmdb
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*/
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template<class K, class V>
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std::pair<K, V> LMDBAL::Cursor<K, V>::last () const {
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std::pair<K, V> result;
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operateCursorRead(result.first, result.second, MDB_LAST, lastMethodName, lastOperationName);
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return result;
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}
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/**
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* \brief Queries the next element from the storage
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*
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* If there was no operation before this method positions the cursor on the first element and returns it
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* so, it's basically doing the same as LMDBAL::Cursor::first().
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*
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* It will also throw LMDBAL::NotFound if you call this method being on the last element
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* or if there are no elements in the database.
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*
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* Notifies the storage of the queried element calling LMDBAL::Storage::discoveredRecord()
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*
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* \returns std::pair where first is element key and second is element value
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*
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* \throws LMDBAL::CursorNotReady thrown if you try to call this method on a closed cursor
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* \throws LMDBAL::NotFound thrown if the cursor already was on the last element or if there are no elements in the storage
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* \throws LMDBAL::Unknown thrown if there was some unexpected problem with lmdb
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*/
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template<class K, class V>
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std::pair<K, V> LMDBAL::Cursor<K, V>::next () const {
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std::pair<K, V> result;
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operateCursorRead(result.first, result.second, MDB_NEXT, nextMethodName, nextOperationName);
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return result;
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}
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/**
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* \brief Queries the previous element from the storage
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*
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* If there was no operation before this method positions the cursor on the last element and returns it
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* so, it's basically doing the same as LMDBAL::Cursor::last().
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*
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* It will also throw LMDBAL::NotFound if you call this method being on the first element
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* or if there are no elements in the database.
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*
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* Notifies the storage of the queried element calling LMDBAL::Storage::discoveredRecord()
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*
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* \returns std::pair where first is element key and second is element value
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*
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* \throws LMDBAL::CursorNotReady thrown if you try to call this method on a closed cursor
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* \throws LMDBAL::NotFound thrown if the cursor already was on the first element or if there are no elements in the storage
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* \throws LMDBAL::Unknown thrown if there was some unexpected problem with lmdb
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*/
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template<class K, class V>
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std::pair<K, V> LMDBAL::Cursor<K, V>::prev () const {
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std::pair<K, V> result;
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operateCursorRead(result.first, result.second, MDB_PREV, prevMethodName, prevOperationName);
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return result;
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}
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/**
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* \brief Returns current cursor element from the storage
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*
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* If there was no operation before this method throws LMDBAL::Unknown for some reason
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*
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* Notifies the storage of the queried element calling LMDBAL::Storage::discoveredRecord()
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*
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* \returns std::pair where first is element key and second is element value
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*
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* \throws LMDBAL::CursorNotReady thrown if you try to call this method on a closed cursor
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* \throws LMDBAL::NotFound probably never thrown but there might be still some corner case I don't know about
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* \throws LMDBAL::Unknown thrown if there was no positioning operation before of if there was some unexpected problem with lmdb
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*/
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template<class K, class V>
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std::pair<K, V> LMDBAL::Cursor<K, V>::current () const {
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std::pair<K, V> result;
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operateCursorRead(result.first, result.second, MDB_GET_CURRENT, currentMethodName, currentOperationName);
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return result;
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}
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/**
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* \brief a private mothod that actually doing all the reading
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*
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* Queries the storage, deserializes the output, notifies the storage of the queried element calling LMDBAL::Storage::discoveredRecord()
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*
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* \param[out] key a reference to an object the key of queried element is going to be assigned
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* \param[out] value a reference to an object the value of queried element is going to be assigned
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* \param[in] operation LMDB cursor <a class="el" href="http://www.lmdb.tech/doc/group__mdb.html#ga1206b2af8b95e7f6b0ef6b28708c9127">operation code</a>
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* \param[in] methodName a name of the method you called it from, just for the exception message if something goes not as expected
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* \param[in] operationName a name of the opeartion, just for the exception message if something goes not as expected
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*
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* \throws LMDBAL::CursorNotReady thrown if you try to call this method on a closed cursor
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* \throws LMDBAL::NotFound mostly thrown if the query wasn't found
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* \throws LMDBAL::Unknown mostly thrown if there was some unexpected problem with lmdb
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*/
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template<class K, class V>
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void LMDBAL::Cursor<K, V>::operateCursorRead(
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K& key,
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V& value,
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MDB_cursor_op operation,
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const std::string& methodName,
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const std::string& operationName
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|
) const {
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if (state == closed)
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storage->throwCursorNotReady(methodName);
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MDB_val mdbKey, mdbValue;
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int result = mdb_cursor_get(cursor, &mdbKey, &mdbValue, operation);
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if (result != MDB_SUCCESS)
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storage->throwNotFoundOrUnknown(result, operationName);
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|
|
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storage->keySerializer.deserialize(mdbKey, key);
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storage->valueSerializer.deserialize(mdbValue, value);
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|
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if (state == openedPrivate)
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storage->discoveredRecord(key, value);
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else
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storage->discoveredRecord(key, value, mdb_cursor_txn(cursor));
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}
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|
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#endif //LMDBAL_CURSOR_HPP
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