Sessions to manage db open state

src/CMakeLists.txt

@@ -4,6 +4,7 @@ set(SOURCES
     base.cpp
     transaction.cpp
     cursorcommon.cpp
+    session.cpp
 )
 
 set(HEADERS
@@ -20,6 +21,7 @@ set(HEADERS
   cache.hpp
   operators.hpp
   transaction.h
+  session.h
 )
 
 target_sources(${LMDBAL_NAME} PRIVATE ${SOURCES})

src/base.cpp

@@ -18,8 +18,10 @@
 
 #include "base.h"
 #include "exceptions.h"
+#include "session.h"
 #include "storage.h"
 #include "transaction.h"
+#include "session.h"
 
 #define UNUSED(x) (void)(x)
 
@@ -39,75 +41,34 @@
  */
 LMDBAL::Base::Base(const QString& _name, uint16_t _mapSize):
     name(_name.toStdString()),
-    opened(false),
+    sessions(),
     size(_mapSize),
     environment(),
     storages(),
-    transactions()
+    transactions(),
+    mutex()
 {}
 
 /**
  * \brief Destroys the database
  */
 LMDBAL::Base::~Base() {
-    close();
+    std::lock_guard lock(mutex);
+
+    for (Session* session : sessions)
+        session->terminate();
+
+    if (opened())
+        deactivate();
 
     for (const std::pair<const std::string, StorageCommon*>& pair : storages)
         delete pair.second;
 }
 
-/**
- * \brief Closes the database
- *
- * Closes all lmdb handles, aborts all public transactions.
- * This function will do nothing on a closed database
- *
- * \exception LMDBAL::Unknown   - thrown if something went wrong aborting transactions
- */
-void LMDBAL::Base::close() {
-    if (opened) {
-        for (const std::pair<TransactionID, Transaction*> pair : transactions) {
-            abortTransaction(pair.first, emptyName);
-            pair.second->reset();
-        }
-
-        for (const std::pair<const std::string, StorageCommon*>& pair : storages)
-            pair.second->close();
-
-        mdb_env_close(environment);
-        transactions.clear();
-        opened = false;
-    }
+LMDBAL::Session LMDBAL::Base::open() {
+    return {this};
 }
 
-/**
- * \brief Opens the database
- *
- * Almost every LMDBAL::Base require it to be opened, this function does it.
- * It also creates the directory for the database if it was an initial launch.
- * This function will do nothing on an opened database
- *
- * \exception LMDBAL::Unknown - thrown if something went wrong opening storages and caches
- */
-void LMDBAL::Base::open() {
-    if (!opened) {
-        mdb_env_create(&environment);
-        QString path = createDirectory();
-
-        mdb_env_set_maxdbs(environment, static_cast<MDB_dbi>(storages.size()));
-        mdb_env_set_mapsize(environment, size * 1024UL * 1024UL);
-        mdb_env_open(environment, path.toStdString().c_str(), 0, 0664);
-
-        TransactionID txn = beginPrivateTransaction(emptyName);
-        for (const std::pair<const std::string, StorageCommon*>& pair : storages) {
-            StorageCommon* storage = pair.second;
-            if (const int rc = storage->open(txn))
-                throw Unknown(name, mdb_strerror(rc));
-        }
-        commitPrivateTransaction(txn, emptyName);
-        opened = true;
-    }
-}
 
 /**
  * \brief Removes database directory
@@ -117,7 +78,7 @@ void LMDBAL::Base::open() {
  * \exception LMDBAL::Opened   - thrown if this function was called on an opened database
  */
 bool LMDBAL::Base::removeDirectory() {
-    if (opened)
+    if (opened())
         throw Opened(name, "remove database directory");
 
     QString path = getPath();
@@ -144,7 +105,7 @@ bool LMDBAL::Base::removeDirectory() {
  * \exception LMDBAL::Directory - if the database couldn't create the folder
  */
 QString LMDBAL::Base::createDirectory() {
-    if (opened)
+    if (opened())
         throw Opened(name, "create database directory");
 
     QString path = getPath();
@@ -183,8 +144,9 @@ QString LMDBAL::Base::getPath() const {
  *
  * \returns true if the database is opened and ready for work, false otherwise
  */
-bool LMDBAL::Base::ready() const {
-    return opened;}
+bool LMDBAL::Base::opened() const {
+    return !sessions.empty();
+}
 
 /**
  * \brief Drops the database
@@ -195,7 +157,7 @@ bool LMDBAL::Base::ready() const {
  * \exception LMDBAL::Unknown   - thrown if something unexpected happend
  */
 void LMDBAL::Base::drop() {
-    if (!opened)
+    if (!opened())
         throw Closed("drop", name);
 
     TransactionID txn = beginPrivateTransaction(emptyName);
@@ -301,7 +263,7 @@ void LMDBAL::Base::commitTransaction(LMDBAL::TransactionID id) {
  * \exception LMDBAL::Unknown   - thrown if something unexpected happened
  */
 LMDBAL::TransactionID LMDBAL::Base::beginReadOnlyTransaction(const std::string& storageName) const {
-    if (!opened)
+    if (!opened())
         throw Closed("beginReadOnlyTransaction", name, storageName);
 
     TransactionID txn = beginPrivateReadOnlyTransaction(storageName);
@@ -326,7 +288,7 @@ LMDBAL::TransactionID LMDBAL::Base::beginReadOnlyTransaction(const std::string&
  * \exception LMDBAL::Unknown   - thrown if something unexpected happened
  */
 LMDBAL::TransactionID LMDBAL::Base::beginTransaction(const std::string& storageName) const {
-    if (!opened)
+    if (!opened())
         throw Closed("beginTransaction", name, storageName);
 
     TransactionID txn = beginPrivateTransaction(storageName);
@@ -351,7 +313,7 @@ LMDBAL::TransactionID LMDBAL::Base::beginTransaction(const std::string& storageN
  * \exception LMDBAL::Unknown   - thrown if something unexpected happened
  */
 void LMDBAL::Base::abortTransaction(LMDBAL::TransactionID id, const std::string& storageName) const {
-    if (!opened)
+    if (!opened())
         throw Closed("abortTransaction", name, storageName);
 
     abortPrivateTransaction(id, storageName);
@@ -374,7 +336,7 @@ void LMDBAL::Base::abortTransaction(LMDBAL::TransactionID id, const std::string&
  * \exception LMDBAL::Unknown   - thrown if something unexpected happened
  */
 void LMDBAL::Base::commitTransaction(LMDBAL::TransactionID id, const std::string& storageName) {
-    if (!opened)
+    if (!opened())
         throw Closed("abortTransaction", name, storageName);
 
     commitPrivateTransaction(id, storageName);
@@ -407,7 +369,7 @@ LMDBAL::TransactionID LMDBAL::Base::beginPrivateReadOnlyTransaction(const std::s
  * \brief Begins writable transaction
  *
  * This function is intended to be called from subordinate storage or cache,
- * it's not accounted in transaction collection, other storages and caches are not notified about this kind of transaction
+ * it's not accounted in the transaction collection, other storages and caches are not notified about this kind of transaction
  *
  * \param[in] storageName   - name of the storage/cache that you begin transaction from, needed just to inform if something went wrong
  *
@@ -428,10 +390,10 @@ LMDBAL::TransactionID LMDBAL::Base::beginPrivateTransaction(const std::string& s
 /**
  * \brief Aborts transaction
  *
- * Terminates transaction cancelling changes.
+ * Terminates transaction, cancelling changes.
  * This is an optimal way to terminate read-only transactions.
  * This function is intended to be called from subordinate storage or cache,
- * it's not accounted in transaction collection, other storages and caches are not notified about this kind of transaction
+ * it's not accounted in the transaction collection, other storages and caches are not notified about this kind of transaction
  *
  * \param[in] id            - transaction ID you want to abort
  * \param[in] storageName   - name of the storage/cache that you begin transaction from, unused here
@@ -458,3 +420,104 @@ void LMDBAL::Base::commitPrivateTransaction(LMDBAL::TransactionID id, const std:
     if (rc != MDB_SUCCESS)
         throw Unknown(name, mdb_strerror(rc), storageName);
 }
+
+/**
+ * \brief Registers session
+ *
+ * Registers the session in the session collection.
+ * If it was the first accounted session, it activates the database
+ *
+ * \exception LMDBAL::Unknown   - thrown if this session was already registered
+ */
+void LMDBAL::Base::registerSession(Session* session) {
+    std::lock_guard lock(mutex);
+
+    if (sessions.empty())
+        activate();
+
+    if (!sessions.insert(session).second)
+        throw Unknown(name, "session already registered");
+}
+
+/**
+ * \brief Unregisters session
+ *
+ * Unregisters the session from the session collection.
+ * If it was the last accounted session, it deactivates the database
+ *
+ * \exception LMDBAL::Unknown   - thrown if this session was not registered
+ */
+void LMDBAL::Base::unregisterSession(Session* session) {
+    std::lock_guard lock(mutex);
+
+    if (sessions.size() == 1)
+        deactivate();
+
+    if (sessions.erase(session) != 1)
+        throw Unknown(name, "session was not registered");
+}
+
+/**
+ * \brief Swaps sessions
+ *
+ * Replaces one session by another in the session collection.
+ *
+ * \exception LMDBAL::Unknown   - thrown if there is some unexpected state with sessions, it means the database is in the wrong state
+ */
+void LMDBAL::Base::replaceSession(Session* closing, Session* opening) {
+    std::lock_guard lock(mutex);
+
+    if (sessions.erase(closing) != 1)
+        throw Unknown(name, "session was not registered");
+
+    if (!sessions.insert(opening).second)
+        throw Unknown(name, "session already registered");
+}
+
+/**
+ * \brief Deactivates the database,
+ *
+ * Closes all lmdb handles, aborts all public transactions.
+ * This function will emit SIGSEGV on a deactivated database
+ *
+ * \exception LMDBAL::Unknown   - thrown if something went wrong aborting transactions
+ */
+void LMDBAL::Base::deactivate() {
+    for (const std::pair<TransactionID, Transaction*> pair : transactions) {
+        abortTransaction(pair.first, emptyName);
+        pair.second->reset();
+    }
+
+    for (const std::pair<const std::string, StorageCommon*>& pair : storages)
+        pair.second->close();
+
+    mdb_env_close(environment);
+    transactions.clear();
+}
+
+/**
+ * \brief Activates the database
+ *
+ * Almost every LMDBAL::Base require it to be opened, this function does it.
+ * It also creates the directory for the database if it was an initial launch.
+ * This function will behave unpredictably on an activated database, possible data corruption.
+ *
+ * \exception LMDBAL::Unknown - thrown if something went wrong opening storages and caches
+ */
+void LMDBAL::Base::activate() {
+    mdb_env_create(&environment);
+    QString path = createDirectory();
+
+    mdb_env_set_maxdbs(environment, static_cast<MDB_dbi>(storages.size()));
+    mdb_env_set_mapsize(environment, size * 1024UL * 1024UL);
+    mdb_env_open(environment, path.toStdString().c_str(), 0, 0664);
+
+    TransactionID txn = beginPrivateTransaction(emptyName);
+    for (const std::pair<const std::string, StorageCommon*>& pair : storages) {
+        StorageCommon* storage = pair.second;
+        if (const int rc = storage->open(txn))
+            throw Unknown(name, mdb_strerror(rc));
+    }
+
+    commitPrivateTransaction(txn, emptyName);
+}

src/base.h

@@ -23,6 +23,8 @@
 #include <string>
 #include <optional>
 #include <limits>
+#include <cstdint>
+#include <mutex>
 
 #include <QString>
 #include <QStandardPaths>
@@ -37,6 +39,7 @@ namespace LMDBAL {
 class StorageCommon;
 class Transaction;
 class WriteTransaction;
+class Session;
 
 template<class T>
 class Serializer;
@@ -54,14 +57,14 @@ class Base {
     friend class StorageCommon;
     friend class Transaction;
     friend class WriteTransaction;
-public:
+    friend class Session;
 
+public:
     Base(const QString& name, uint16_t mapSize = 10);
     ~Base();
 
-    void open();
-    void close();
-    bool ready() const;
+    Session open();
+    bool opened() const;
     bool removeDirectory();
     QString createDirectory();
     QString getName() const;
@@ -84,8 +87,9 @@ public:
     LMDBAL::Cache<K, V>* getCache(const std::string& storageName);
 
 private:
-    typedef std::map<std::string, LMDBAL::StorageCommon *> Storages;  /**<\brief Storage and Cache pointers are saved in the std::map*/
-    typedef std::map<TransactionID, Transaction*> Transactions; /**<\brief Piblic transaction IDs are saved in the std::set*/
+    typedef std::map<std::string, LMDBAL::StorageCommon *> Storages;    /**<\brief Storage and Cache pointers are saved in the std::map*/
+    typedef std::map<TransactionID, Transaction*> Transactions;         /**<\brief Public transaction IDs are saved in the std::map*/
+    typedef std::set<Session*> Sessions;                                /**<\brief Sessions are saved in the std::set*/
 
     void commitTransaction(TransactionID id);
     void abortTransaction(TransactionID id) const;
@@ -99,13 +103,21 @@ private:
     void commitPrivateTransaction(TransactionID id, const std::string& storageName);
     void abortPrivateTransaction(TransactionID id, const std::string& storageName) const;
 
+    void registerSession(Session* session);
+    void unregisterSession(Session* session);
+    void replaceSession(Session* closing, Session* opening);
+
+    void activate();
+    void deactivate();
+
 private:
     std::string name;                                           /**<\brief Name of this database*/
-    bool opened;                                                /**<\brief State of this database*/
+    Sessions sessions;                                          /**<\brief Opened session pointers*/
     uint16_t size;                                              /**<\brief lmdb map size in MiB*/
     MDB_env* environment;                                       /**<\brief lmdb environment handle*/
     Storages storages;                                          /**<\brief Registered storages and caches*/
     mutable Transactions transactions;                          /**<\brief Active public transactions*/
+    std::mutex mutex;                                           /**<\brief Mutex for thread safety*/
 
     inline static const std::string emptyName = "";             /**<\brief Empty string for general fallback purposes*/
 };
@@ -132,7 +144,7 @@ private:
  */
 template <class K, class V>
 LMDBAL::Storage<K, V>* LMDBAL::Base::addStorage(const std::string& storageName, bool duplicates) {
-    if (opened)
+    if (opened())
         throw Opened(name, "add storage " + storageName);
 
     auto storage = new Storage<K, V>(this, storageName, duplicates);
@@ -160,7 +172,7 @@ LMDBAL::Storage<K, V>* LMDBAL::Base::addStorage(const std::string& storageName,
  */
 template<class K, class V>
 LMDBAL::Cache<K, V> * LMDBAL::Base::addCache(const std::string& storageName) {
-    if (opened)
+    if (opened())
         throw Opened(name, "add cache " + storageName);
 
     auto cache = new Cache<K, V>(this, storageName, false);

src/session.cpp

@@ -0,0 +1,73 @@
+/*
+* LMDB Abstraction Layer.
+ * Copyright (C) 2023  Yury Gubich <blue@macaw.me>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "session.h"
+
+LMDBAL::Session::Session():
+    parent(nullptr) {}
+
+LMDBAL::Session::Session(Base* parent):
+    parent(parent)
+{
+    parent->registerSession(this);
+}
+
+LMDBAL::Session::Session(Session&& other):
+    parent(other.parent)
+{
+    if (parent)
+        parent->replaceSession(&other, this);
+}
+
+LMDBAL::Session::~Session() {
+    if (parent)
+        parent->unregisterSession(this);
+}
+
+LMDBAL::Session& LMDBAL::Session::operator = (Session&& other) {
+    if (parent)
+        if (other.parent)
+            parent->unregisterSession(&other);
+        else
+            parent->unregisterSession(this);
+    else
+        if (other.parent)
+            other.parent->replaceSession(&other, this);
+
+    parent = other.parent;
+    other.terminate();
+
+    return *this;
+}
+
+void LMDBAL::Session::close() {
+    if (!parent)
+        return;
+
+    parent->unregisterSession(this);
+    terminate();
+}
+
+bool LMDBAL::Session::opened() const {
+    return parent != nullptr;
+}
+
+void LMDBAL::Session::terminate() {
+    parent = nullptr;
+}
+

src/session.h

@@ -0,0 +1,47 @@
+/*
+* LMDB Abstraction Layer.
+ * Copyright (C) 2023  Yury Gubich <blue@macaw.me>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "base.h"
+
+namespace LMDBAL {
+
+class Session {
+    friend class Base;
+public:
+    explicit Session();
+    ~Session();
+    Session(const Session&) = delete;
+    Session(Session&&);
+
+    Session& operator = (const Session&) = delete;
+    Session& operator = (Session&&);
+
+    void close();
+    bool opened() const;
+
+private:
+    Base* parent;
+
+private:
+    Session(Base* parent);
+    void terminate();
+};
+
+}

src/storagecommon.cpp

@@ -356,7 +356,7 @@ const std::string & LMDBAL::StorageCommon::dbName() const {
  * \returns true if database is ipened, false otherwise
  */
 bool LMDBAL::StorageCommon::isDBOpened() const {
-    return db->opened;}
+    return db->opened();}
 
 /**
  * \brief Throws LMDBAL::Unknown