[Spatialite provider] Properly destroy QgsSpatiaLiteConnPool singleton at provider unloading. Should fix frequent crash in PyQgsServerWMS on Travis (fixes #17447)

src/providers/spatialite/qgsspatialiteconnpool.cpp

@@ -13,11 +13,30 @@
  *                                                                         *
  ***************************************************************************/
 
+#include <QMutex>
+#include <QMutexLocker>
+
 #include "qgsspatialiteconnpool.h"
 
-QgsSpatiaLiteConnPool QgsSpatiaLiteConnPool::sInstance;
+QgsSpatiaLiteConnPool *QgsSpatiaLiteConnPool::sInstance = nullptr;
 
 QgsSpatiaLiteConnPool *QgsSpatiaLiteConnPool::instance()
 {
-  return &sInstance;
+  if ( ! sInstance )
+  {
+    static QMutex sMutex;
+    QMutexLocker locker( &sMutex );
+    if ( ! sInstance )
+    {
+      sInstance = new QgsSpatiaLiteConnPool();
+    }
+  }
+  return sInstance;
+}
+
+// static public
+void QgsSpatiaLiteConnPool::cleanupInstance()
+{
+  delete sInstance;
+  sInstance = nullptr;
 }

src/providers/spatialite/qgsspatialiteconnpool.h

@@ -68,9 +68,19 @@ class QgsSpatiaLiteConnPoolGroup : public QObject, public QgsConnectionPoolGroup
 //! SpatiaLite connection pool - singleton
 class QgsSpatiaLiteConnPool : public QgsConnectionPool<QgsSqliteHandle *, QgsSpatiaLiteConnPoolGroup>
 {
-    static QgsSpatiaLiteConnPool sInstance;
+    static QgsSpatiaLiteConnPool *sInstance;
   public:
     static QgsSpatiaLiteConnPool *instance();
+
+    // Singleton cleanup
+    //
+    // Make sure nobody is using the instance before calling
+    // this function.
+    //
+    // WARNING: concurrent call from multiple threads may result
+    //          in double-free of the instance.
+    //
+    static void cleanupInstance();
 };
 
 

src/providers/spatialite/qgsspatialiteprovider.cpp

@@ -5900,6 +5900,7 @@ QGISEXTERN QString getStyleById( const QString &uri, QString styleId, QString &e
 
 QGISEXTERN void cleanupProvider()
 {
+  QgsSpatiaLiteConnPool::cleanupInstance();
   QgsSqliteHandle::closeAll();
 }