bpo-44958: Only reset sqlite3 statements when needed

Lib/sqlite3/test/test_regression.py

@@ -124,13 +124,14 @@ def test_type_map_usage(self):
  """
  SELECT = "select * from foo"
  con = sqlite.connect(":memory:",detect_types=sqlite.PARSE_DECLTYPES)
- con.execute("create table foo(bar timestamp)")
- con.execute("insert into foo(bar) values (?)", (datetime.datetime.now(),))
- con.execute(SELECT).close()
- con.execute("drop table foo")
- con.execute("create table foo(bar integer)")
- con.execute("insert into foo(bar) values (5)")
- con.execute(SELECT).close()
+ cur = con.cursor()
+ cur.execute("create table foo(bar timestamp)")
+ cur.execute("insert into foo(bar) values (?)", (datetime.datetime.now(),))
+ cur.execute(SELECT)
+ cur.execute("drop table foo")
+ cur.execute("create table foo(bar integer)")
+ cur.execute("insert into foo(bar) values (5)")
+ cur.execute(SELECT)
 
  def test_bind_mutating_list(self):
  # Issue41662: Crash when mutate a list of parameters during iteration.
@@ -435,6 +436,40 @@ def test_return_empty_bytestring(self):
  val = cur.fetchone()[0]
  self.assertEqual(val, b'')
 
+ def test_table_lock_cursor_replace_stmt(self):
+ con = sqlite.connect(":memory:")
+ cur = con.cursor()
+ cur.execute("create table t(t)")
+ cur.executemany("insert into t values(?)", ((v,) for v in range(5)))
+ con.commit()
+ cur.execute("select t from t")
+ cur.execute("drop table t")
+ con.commit()
+
+ def test_table_lock_cursor_dealloc(self):
+ con = sqlite.connect(":memory:")
+ con.execute("create table t(t)")
+ con.executemany("insert into t values(?)", ((v,) for v in range(5)))
+ con.commit()
+ cur = con.execute("select t from t")
+ del cur
+ con.execute("drop table t")
+ con.commit()
+
+ def test_table_lock_cursor_non_readonly_select(self):
+ con = sqlite.connect(":memory:")
+ con.execute("create table t(t)")
+ con.executemany("insert into t values(?)", ((v,) for v in range(5)))
+ con.commit()
+ def dup(v):
+ con.execute("insert into t values(?)", (v,))
+ return
+ con.create_function("dup", 1, dup)
+ cur = con.execute("select dup(t) from t")
+ del cur
+ con.execute("drop table t")
+ con.commit()
+
 
 if __name__ == "__main__":
  unittest.main()

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;

Modules/_sqlite/statement.c

@@ -360,23 +360,31 @@ pysqlite_statement_bind_parameters(pysqlite_state *state,
  }
 }
 
-int pysqlite_statement_reset(pysqlite_Statement* self)
+void
+pysqlite_statement_reset(pysqlite_Statement *self)
 {
- int rc;
+ sqlite3_stmt *stmt = self->st;
+ if (stmt == NULL || self->in_use == 0){
+ return;
+ }
 
- rc = SQLITE_OK;
+#if SQLITE_VERSION_NUMBER >= 3020000
+ /* Check if the statement has been run (that is, sqlite3_step() has been
+ * called at least once). Third parameter is non-zero in order to reset the
+ * run count. */
+ if (sqlite3_stmt_status(stmt, SQLITE_STMTSTATUS_RUN, 1) == 0){
+ return;
+ }
+#endif
 
-if (self->in_use && self->st){
-Py_BEGIN_ALLOW_THREADS
-rc = sqlite3_reset(self->st);
-Py_END_ALLOW_THREADS
+int rc;
+ Py_BEGIN_ALLOW_THREADS
+ rc = sqlite3_reset(stmt);
+ Py_END_ALLOW_THREADS
 
- if (rc == SQLITE_OK){
- self->in_use = 0;
- }
+ if (rc == SQLITE_OK){
+ self->in_use = 0;
  }
-
- return rc;
 }
 
 void pysqlite_statement_mark_dirty(pysqlite_Statement* self)

Modules/_sqlite/statement.h

@@ -44,7 +44,7 @@ void pysqlite_statement_bind_parameters(pysqlite_state *state,
  pysqlite_Statement *self,
  PyObject *parameters);
 
-int pysqlite_statement_reset(pysqlite_Statement* self);
+void pysqlite_statement_reset(pysqlite_Statement *self);
 void pysqlite_statement_mark_dirty(pysqlite_Statement* self);
 
 int pysqlite_statement_setup_types(PyObject *module);