Speed up exception propagation

Avoid catch (...) with re-throw as it turns that this is very slow because it
throws a new exception and the unwinder starts from scratch. Instead use stack
allocated objects and cleaning destructors to restore state before continuing
with the propagation of exceptions.

Change-Id: I6d95026bcd60b58cb6258a9dae28623a46739532
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

1 files changed, 36 insertions, 19 deletions

diff --git a/src/imports/localstorage/plugin.cpp b/src/imports/localstorage/plugin.cpp
index 84bcb756e8..9a0528a28f 100644
--- a/src/imports/localstorage/plugin.cpp
+++ b/src/imports/localstorage/plugin.cpp
@@ -322,6 +322,35 @@ static ReturnedValue qmlsqldatabase_executeSql(SimpleCallContext *ctx)
     return result.asReturnedValue();
 }
 
+struct TransactionRollback {
+    QSqlDatabase *db;
+    bool *inTransactionFlag;
+
+    TransactionRollback(QSqlDatabase *database, bool *transactionFlag)
+        : db(database)
+        , inTransactionFlag(transactionFlag)
+    {
+        if (inTransactionFlag)
+            *inTransactionFlag = true;
+    }
+
+    ~TransactionRollback()
+    {
+        if (inTransactionFlag)
+            *inTransactionFlag = false;
+        if (db)
+            db->rollback();
+    }
+
+    void clear() {
+        db = 0;
+        if (inTransactionFlag)
+            *inTransactionFlag = false;
+        inTransactionFlag = 0;
+    }
+};
+
+
 static ReturnedValue qmlsqldatabase_changeVersion(SimpleCallContext *ctx)
 {
     if (ctx->callData->argc < 2)
@@ -349,7 +378,6 @@ static ReturnedValue qmlsqldatabase_changeVersion(SimpleCallContext *ctx)
     w->type = QQmlSqlDatabaseWrapper::Query;
     w->database = db;
     w->version = r->version;
-    w->inTransaction = true;
 
     bool ok = true;
     if (!!callback) {
@@ -359,12 +387,10 @@ static ReturnedValue qmlsqldatabase_changeVersion(SimpleCallContext *ctx)
         ScopedCallData callData(scope, 1);
         callData->thisObject = engine->global();
         callData->args[0] = w;
-        try {
-            callback->call(callData);
-        } catch (...) {
-            db.rollback();
-            ctx->rethrowException();
-        }
+
+        TransactionRollback rollbackOnException(&db, &w->inTransaction);
+        callback->call(callData);
+        rollbackOnException.clear();
         if (!db.commit()) {
             db.rollback();
             V4THROW_SQL(SQLEXCEPTION_UNKNOWN_ERR,QQmlEngine::tr("SQL transaction failed"));
@@ -373,8 +399,6 @@ static ReturnedValue qmlsqldatabase_changeVersion(SimpleCallContext *ctx)
         }
     }
 
-    w->inTransaction = false;
-
     if (ok) {
         w->version = to_version;
 #ifndef QT_NO_SETTINGS
@@ -408,22 +432,15 @@ static ReturnedValue qmlsqldatabase_transaction_shared(SimpleCallContext *ctx, b
     w->database = db;
     w->version = r->version;
     w->readonly = readOnly;
-    w->inTransaction = true;
 
     db.transaction();
     if (callback) {
         ScopedCallData callData(scope, 1);
         callData->thisObject = engine->global();
         callData->args[0] = w;
-        try {
-            callback->call(callData);
-        } catch (...) {
-            w->inTransaction = false;
-            db.rollback();
-            ctx->rethrowException();
-        }
-
-        w->inTransaction = false;
+        TransactionRollback rollbackOnException(&db, &w->inTransaction);
+        callback->call(callData);
+        rollbackOnException.clear();
 
         if (!db.commit())
             db.rollback();