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#ifndef READWRITELOCKER_H
#define READWRITELOCKER_H
#include "coreSQLiteStudio_global.h"
#include "dialect.h"
class QReadLocker;
class QWriteLocker;
class QReadWriteLock;
/**
* @brief The ReadWriteLocker class
*
* This class behaves pretty much like QReadLocker or QWriteLocker
* (it actually uses those internally), except it can be either
* of those and this is to be decided at the moment of creation.
* Therefore the locker can work as read or write locker depending
* on an external condition.
* There's also a possibility to not lock anything as a third
* choice of working mode, so this also can be decided
* at construction moment.
*/
class API_EXPORT ReadWriteLocker
{
public:
enum Mode
{
READ,
WRITE,
NONE
};
ReadWriteLocker(QReadWriteLock* lock, Mode mode);
ReadWriteLocker(QReadWriteLock* lock, const QString& query, Dialect dialect, bool noLock);
virtual ~ReadWriteLocker();
/**
* @brief Provides required locking mode for given query.
* @param query Query to be executed.
* @return Locking mode: READ or WRITE.
*
* Given the query this method analyzes what is the query and provides information if the query
* will do some changes on the database, or not. Then it returns proper locking mode that should
* be used for this query execution.
*
* Query execution methods from this class check if lock mode of the query to be executed isn't
* in conflict with the lock being currently applied on the dbOperLock (if any is applied at the moment).
*
* This method works on a very simple rule. It assumes that queries: SELECT, ANALYZE, EXPLAIN,
* and PRAGMA - are read-only, while all other queries are read-write.
* In case of PRAGMA this is not entirely true, but it's not like using PRAGMA for changing
* some setting would cause database state inconsistency. At least not from perspective of SQLiteStudio.
*
* In case of WITH statement it filters out the "WITH clause" and then checks for SELECT keyword.
*/
static ReadWriteLocker::Mode getMode(const QString& query, Dialect dialect, bool noLock);
private:
void init(QReadWriteLock* lock, Mode mode);
QReadLocker* readLocker = nullptr;
QWriteLocker* writeLocker = nullptr;
};
#endif // READWRITELOCKER_H
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