[tracker] libtracker-data: Add explicit calls to grab/release an stmt

[Carlos Garnacho <carlosg src gnome org>]

commit 0d6502a3ea307a0d40c6ffabbf92ddddbd069401
Author: Carlos Garnacho <carlosg gnome org>
Date:   Sun Nov 6 14:29:35 2016 +0100

    libtracker-data: Add explicit calls to grab/release an stmt
    
    An stmt can just be grabbed once at a time, and will ref both
    the stmt and its DB interface for as long as the stmt is grabbed.
    After releasing both refs will be dropped (and stmt_is_used set
    back to FALSE), so it will be ensured that a database connection
    lives as long as there are active cursors grabbing an statement.

 src/libtracker-data/tracker-db-interface-sqlite.c |   31 +++++++++++++++-----
 1 files changed, 23 insertions(+), 8 deletions(-)
---
diff --git a/src/libtracker-data/tracker-db-interface-sqlite.c 
b/src/libtracker-data/tracker-db-interface-sqlite.c
index e6eef85..744cb2d 100644
--- a/src/libtracker-data/tracker-db-interface-sqlite.c
+++ b/src/libtracker-data/tracker-db-interface-sqlite.c
@@ -2392,6 +2392,27 @@ tracker_db_statement_sqlite_new (TrackerDBInterface *db_interface,
        return stmt;
 }
 
+static TrackerDBStatement *
+tracker_db_statement_sqlite_grab (TrackerDBStatement *stmt)
+{
+       g_assert (!stmt->stmt_is_used);
+       stmt->stmt_is_used = TRUE;
+       g_object_ref (stmt->db_interface);
+       return g_object_ref (stmt);
+}
+
+static void
+tracker_db_statement_sqlite_release (TrackerDBStatement *stmt)
+{
+       TrackerDBInterface *iface = stmt->db_interface;
+
+       g_assert (stmt->stmt_is_used);
+       stmt->stmt_is_used = FALSE;
+       tracker_db_statement_sqlite_reset (stmt);
+       g_object_unref (stmt);
+       g_object_unref (iface);
+}
+
 static void
 tracker_db_cursor_close (TrackerDBCursor *cursor)
 {
@@ -2408,12 +2429,7 @@ tracker_db_cursor_close (TrackerDBCursor *cursor)
        g_atomic_int_add (&iface->n_active_cursors, -1);
 
        tracker_db_interface_lock (iface);
-
-       cursor->ref_stmt->stmt_is_used = FALSE;
-       tracker_db_statement_sqlite_reset (cursor->ref_stmt);
-       g_object_unref (cursor->ref_stmt);
-       cursor->ref_stmt = NULL;
-
+       g_clear_pointer (&cursor->ref_stmt, tracker_db_statement_sqlite_release);
        tracker_db_interface_unlock (iface);
 }
 
@@ -2538,8 +2554,7 @@ tracker_db_cursor_sqlite_new (TrackerDBStatement  *ref_stmt,
        cursor->finished = FALSE;
 
        cursor->stmt = ref_stmt->stmt;
-       ref_stmt->stmt_is_used = TRUE;
-       cursor->ref_stmt = g_object_ref (ref_stmt);
+       cursor->ref_stmt = tracker_db_statement_sqlite_grab (ref_stmt);
 
        if (types) {
                gint i;