bpo-44958: Only reset `sqlite3` statements when needed (GH-27844)

1 files changed, 19 insertions, 26 deletions

diff --git a/Modules/_sqlite/cursor.c b/Modules/_sqlite/cursor.c
index 38ccdcf..9bac607 100644
--- a/Modules/_sqlite/cursor.c
+++ b/Modules/_sqlite/cursor.c
@@ -104,12 +104,7 @@ cursor_clear(pysqlite_Cursor *self)
     Py_CLEAR(self->row_cast_map);
     Py_CLEAR(self->lastrowid);
     Py_CLEAR(self->row_factory);
-    if (self->statement) {
-        /* Reset the statement if the user has not closed the cursor */
-        pysqlite_statement_reset(self->statement);
-        Py_CLEAR(self->statement);
-    }
-
+    Py_CLEAR(self->statement);
     return 0;
 }
 
@@ -121,6 +116,14 @@ cursor_dealloc(pysqlite_Cursor *self)
     if (self->in_weakreflist != NULL) {
         PyObject_ClearWeakRefs((PyObject*)self);
     }
+    if (self->statement) {
+        /* A SELECT query will lock the affected database table(s), so we need
+         * to reset the statement to unlock the database before disappearing */
+        sqlite3_stmt *stmt = self->statement->st;
+        if (sqlite3_stmt_readonly(stmt)) {
+            pysqlite_statement_reset(self->statement);
+        }
+    }
     tp->tp_clear((PyObject *)self);
     tp->tp_free(self);
     Py_DECREF(tp);
@@ -515,18 +518,19 @@ _pysqlite_query_execute(pysqlite_Cursor* self, int multiple, PyObject* operation
         }
     }
 
-    if (self->statement != NULL) {
-        /* There is an active statement */
-        pysqlite_statement_reset(self->statement);
-    }
-
     /* reset description and rowcount */
     Py_INCREF(Py_None);
     Py_SETREF(self->description, Py_None);
     self->rowcount = 0L;
 
     if (self->statement) {
-        (void)pysqlite_statement_reset(self->statement);
+        /* A SELECT query will lock the affected database table(s), so we need
+         * to reset the statement to unlock the database before switching
+         * statements */
+        sqlite3_stmt *stmt = self->statement->st;
+        if (sqlite3_stmt_readonly(stmt)) {
+            pysqlite_statement_reset(self->statement);
+        }
     }
 
     PyObject *stmt = get_statement_from_cache(self, operation);
@@ -549,8 +553,6 @@ _pysqlite_query_execute(pysqlite_Cursor* self, int multiple, PyObject* operation
             goto error;
         }
     }
-
-    pysqlite_statement_reset(self->statement);
     pysqlite_statement_mark_dirty(self->statement);
 
     /* We start a transaction implicitly before a DML statement.
@@ -570,6 +572,7 @@ _pysqlite_query_execute(pysqlite_Cursor* self, int multiple, PyObject* operation
             break;
         }
 
+        pysqlite_statement_reset(self->statement);
         pysqlite_statement_mark_dirty(self->statement);
 
         pysqlite_statement_bind_parameters(state, self->statement, parameters);
@@ -587,7 +590,6 @@ _pysqlite_query_execute(pysqlite_Cursor* self, int multiple, PyObject* operation
                     PyErr_Clear();
                 }
             }
-            (void)pysqlite_statement_reset(self->statement);
             _pysqlite_seterror(state, self->connection->db);
             goto error;
         }
@@ -646,13 +648,9 @@ _pysqlite_query_execute(pysqlite_Cursor* self, int multiple, PyObject* operation
         }
 
         if (rc == SQLITE_DONE && !multiple) {
-            pysqlite_statement_reset(self->statement);
             Py_CLEAR(self->statement);
         }
 
-        if (multiple) {
-            pysqlite_statement_reset(self->statement);
-        }
         Py_XDECREF(parameters);
     }
 
@@ -804,7 +802,6 @@ pysqlite_cursor_iternext(pysqlite_Cursor *self)
     sqlite3_stmt *stmt = self->statement->st;
     assert(stmt != NULL);
     if (sqlite3_data_count(stmt) == 0) {
-        (void)pysqlite_statement_reset(self->statement);
         Py_CLEAR(self->statement);
         return NULL;
     }
@@ -815,7 +812,7 @@ pysqlite_cursor_iternext(pysqlite_Cursor *self)
     }
     int rc = pysqlite_step(stmt);
     if (rc == SQLITE_DONE) {
-        (void)pysqlite_statement_reset(self->statement);
+        Py_CLEAR(self->statement);
     }
     else if (rc != SQLITE_ROW) {
         (void)_pysqlite_seterror(self->connection->state,
@@ -985,11 +982,7 @@ pysqlite_cursor_close_impl(pysqlite_Cursor *self, PyTypeObject *cls)
         return NULL;
     }
 
-    if (self->statement) {
-        (void)pysqlite_statement_reset(self->statement);
-        Py_CLEAR(self->statement);
-    }
-
+    Py_CLEAR(self->statement);
     self->closed = 1;
 
     Py_RETURN_NONE;