From ccc4eb8530727d5b9701f46ef4d79660b872a66e Mon Sep 17 00:00:00 2001
From: Eugene Kosov <claprix@yandex.ru>
Date: Sun, 3 May 2020 01:05:15 +0300
Subject: [PATCH] MDEV-22438 add a function similar to std::make_scope_exit()

The idea was borrowed from http://wg21.link/p0052

scope_exit class is a helper, its name is hidden from user in
the namespace detail.

Alternative implementation of scope_exit with std::function
looks slower on goldbolt.org as it may require allocation, etc.
scope_exit doesn't need to own a callable, so beeing a pointer
is enough. And std::decay produces such a pointer from callable.
---
 include/scope.h                       | 66 +++++++++++++++++++++++++++
 storage/innobase/handler/ha_innodb.cc |  6 +--
 2 files changed, 68 insertions(+), 4 deletions(-)
 create mode 100644 include/scope.h

diff --git a/include/scope.h b/include/scope.h
new file mode 100644
index 00000000000..b9e2e96ae5c
--- /dev/null
+++ b/include/scope.h
@@ -0,0 +1,66 @@
+/*
+   Copyright (c) 2020, MariaDB
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License
+   as published by the Free Software Foundation; version 2 of
+   the License.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335  USA
+*/
+
+#pragma once
+
+#include <type_traits>
+#include <utility>
+
+namespace detail
+{
+
+template <typename Callable> class scope_exit
+{
+public:
+  template <typename F>
+  explicit scope_exit(F &&f) : function_(std::forward<F>(f))
+  {
+  }
+
+  scope_exit(scope_exit &&rhs)
+      : function_(std::move(rhs.function_)), engaged_(rhs.engaged_)
+  {
+    rhs.release();
+  }
+
+  scope_exit(const scope_exit &)= delete;
+  scope_exit &operator=(scope_exit &&)= delete;
+  scope_exit &operator=(const scope_exit &)= delete;
+
+  void release() { engaged_= false; }
+
+  ~scope_exit()
+  {
+    if (engaged_)
+      function_();
+  }
+
+private:
+  Callable function_;
+  bool engaged_= true;
+};
+
+} // end namespace detail
+
+template <typename Callable>
+detail::scope_exit<typename std::decay<Callable>::type>
+make_scope_exit(Callable &&f)
+{
+  return detail::scope_exit<typename std::decay<Callable>::type>(
+      std::forward<Callable>(f));
+}
diff --git a/storage/innobase/handler/ha_innodb.cc b/storage/innobase/handler/ha_innodb.cc
index 777e93997e0..06d63fbe84a 100644
--- a/storage/innobase/handler/ha_innodb.cc
+++ b/storage/innobase/handler/ha_innodb.cc
@@ -55,6 +55,7 @@ this program; if not, write to the Free Software Foundation, Inc.,
 #include <mysql/service_thd_alloc.h>
 #include <mysql/service_thd_wait.h>
 #include "field.h"
+#include "scope.h"
 
 // MYSQL_PLUGIN_IMPORT extern my_bool lower_case_file_system;
 // MYSQL_PLUGIN_IMPORT extern char mysql_unpacked_real_data_home[];
@@ -10881,6 +10882,7 @@ create_table_info_t::create_table_def()
 	}
 
 	heap = mem_heap_create(1000);
+	auto _ = make_scope_exit([heap]() { mem_heap_free(heap); });
 
 	ut_d(bool have_vers_start = false);
 	ut_d(bool have_vers_end = false);
@@ -10941,7 +10943,6 @@ create_table_info_t::create_table_def()
 					" must be below 256."
 					" Unsupported code " ULINTPF ".",
 					charset_no);
-				mem_heap_free(heap);
 				dict_mem_table_free(table);
 
 				DBUG_RETURN(ER_CANT_CREATE_TABLE);
@@ -10972,7 +10973,6 @@ create_table_info_t::create_table_def()
 				 field->field_name.str);
 err_col:
 			dict_mem_table_free(table);
-			mem_heap_free(heap);
 			ut_ad(trx_state_eq(m_trx, TRX_STATE_NOT_STARTED));
 			DBUG_RETURN(HA_ERR_GENERIC);
 		}
@@ -11100,8 +11100,6 @@ err_col:
 				DBUG_SUICIDE(););
 	}
 
-	mem_heap_free(heap);
-
 	DBUG_EXECUTE_IF("ib_create_err_tablespace_exist",
 			err = DB_TABLESPACE_EXISTS;);