Sqlite: Add busy handler

A busy handler is much more flexible than a timeout. In most cases we can
remove the busy exception handling code.

Change-Id: I59666ccfbd380a341412e3d25e6716b07097bf3c
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

src/libs/sqlite/sqlitedatabase.cpp

@@ -61,7 +61,7 @@ Database::Database()
 }
 
 Database::Database(Utils::PathString &&databaseFilePath, JournalMode journalMode)
-    : Database(std::move(databaseFilePath), 1000ms, journalMode)
+    : Database{std::move(databaseFilePath), 0ms, journalMode}
 {}
 
 Database::Database(Utils::PathString &&databaseFilePath,
@@ -89,7 +89,10 @@ void Database::open()
 {
     m_databaseBackend.open(m_databaseFilePath, m_openMode);
     m_databaseBackend.setJournalMode(m_journalMode);
+    if (m_busyTimeout > 0ms)
         m_databaseBackend.setBusyTimeout(m_busyTimeout);
+    else
+        m_databaseBackend.registerBusyHandler();
     registerTransactionStatements();
     initializeTables();
     m_isOpen = true;

src/libs/sqlite/sqlitedatabase.h

@@ -55,12 +55,12 @@ public:
     using MutexType = std::mutex;
     using ReadStatement = Sqlite::ReadStatement;
     using WriteStatement = Sqlite::WriteStatement;
+    using BusyHandler = DatabaseBackend::BusyHandler;
 
     Database();
+    Database(Utils::PathString &&databaseFilePath, JournalMode journalMode = JournalMode::Wal);
     Database(Utils::PathString &&databaseFilePath,
-             JournalMode journalMode);
-    Database(Utils::PathString &&databaseFilePath,
-             std::chrono::milliseconds busyTimeout = 1000ms,
+             std::chrono::milliseconds busyTimeout,
              JournalMode journalMode = JournalMode::Wal);
     ~Database();
 
@@ -132,6 +132,11 @@ public:
     void setAttachedTables(const Utils::SmallStringVector &tables) override;
     void applyAndUpdateSessions() override;
 
+    void setBusyHandler(BusyHandler busyHandler)
+    {
+        m_databaseBackend.setBusyHandler(std::move(busyHandler));
+    }
+
     SessionChangeSets changeSets() const;
 
 private:

src/libs/sqlite/sqlitedatabasebackend.cpp

@@ -37,15 +37,24 @@
 
 #include "sqlite3.h"
 
+#include <chrono>
+#include <thread>
+
 extern "C" {
 int sqlite3_carray_init(sqlite3 *db, char **pzErrMsg, const sqlite3_api_routines *pApi);
 }
 
 namespace Sqlite {
 
+using namespace std::literals;
+
 DatabaseBackend::DatabaseBackend(Database &database)
     : m_database(database)
     , m_databaseHandle(nullptr)
+    , m_busyHandler([](int) {
+        std::this_thread::sleep_for(10ms);
+        return true;
+    })
 {
 }
 
@@ -197,28 +206,24 @@ void DatabaseBackend::closeWithoutException()
     }
 }
 
+namespace {
+
+int busyHandlerCallback(void *userData, int counter)
+{
+    auto &&busyHandler = *static_cast<DatabaseBackend::BusyHandler *>(userData);
+
+    return busyHandler(counter);
+}
+
+} // namespace
+
 void DatabaseBackend::registerBusyHandler()
 {
-    int resultCode = sqlite3_busy_handler(sqliteDatabaseHandle(), &busyHandlerCallback, nullptr);
+    int resultCode = sqlite3_busy_handler(sqliteDatabaseHandle(), &busyHandlerCallback, &m_busyHandler);
 
     checkIfBusyTimeoutWasSet(resultCode);
 }
 
-void DatabaseBackend::registerRankingFunction()
-{
-}
-
-int DatabaseBackend::busyHandlerCallback(void *, int counter)
-{
-    Q_UNUSED(counter)
-#ifdef QT_DEBUG
-    //qWarning() << "Busy handler invoked" << counter << "times!";
-#endif
-    QThread::msleep(10);
-
-    return true;
-}
-
 void DatabaseBackend::checkForOpenDatabaseWhichCanBeClosed()
 {
     if (m_databaseHandle == nullptr)
@@ -416,6 +421,12 @@ void DatabaseBackend::resetUpdateHook()
     sqlite3_update_hook(m_databaseHandle, nullptr, nullptr);
 }
 
+void DatabaseBackend::setBusyHandler(DatabaseBackend::BusyHandler &&busyHandler)
+{
+    m_busyHandler = std::move(busyHandler);
+    registerBusyHandler();
+}
+
 void DatabaseBackend::throwExceptionStatic(const char *whatHasHappens)
 {
     throw Exception(whatHasHappens);

src/libs/sqlite/sqlitedatabasebackend.h

@@ -41,6 +41,8 @@ class Database;
 class SQLITE_EXPORT DatabaseBackend
 {
 public:
+    using BusyHandler = std::function<bool(int count)>;
+
     DatabaseBackend(Database &database);
     ~DatabaseBackend();
 
@@ -90,15 +92,16 @@ public:
         void (*callback)(void *object, int, char const *database, char const *, long long rowId));
     void resetUpdateHook();
 
+    void setBusyHandler(BusyHandler &&busyHandler);
+
+    void registerBusyHandler();
+
 protected:
     bool databaseIsOpen() const;
 
     void setPragmaValue(Utils::SmallStringView pragma, Utils::SmallStringView value);
     Utils::SmallString pragmaValue(Utils::SmallStringView pragma);
 
-    void registerBusyHandler();
-    void registerRankingFunction();
-    static int busyHandlerCallback(void*, int counter);
 
     void checkForOpenDatabaseWhichCanBeClosed();
     void checkDatabaseClosing(int resultCode);
@@ -126,6 +129,7 @@ protected:
 private:
     Database &m_database;
     sqlite3 *m_databaseHandle;
+    BusyHandler m_busyHandler;
 };
 
 } // namespace Sqlite