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chromium / chromium / src / lkgr / . / base / auto_reset.h
blob: cfd803b7d66855293654f34219694509fffb7fb4 [file] [log] [blame]
Avi Drissmane4622aa2022-09-08 20:36:06[diff] [blame]1// Copyright 2011 The Chromium Authors
[email protected]5be7da242009-11-20 23:16:26[diff] [blame]2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#ifndef BASE_AUTO_RESET_H_
6#define BASE_AUTO_RESET_H_
7
Sam McNally54bc0282017-12-13 02:42:29[diff] [blame]8#include <utility>
9
Peter Kasting0bca80f2023-03-07 04:37:55[diff] [blame]10#include "base/check_op.h"
Keishi Hattori488b7602022-05-02 13:09:31[diff] [blame]11#include "base/memory/raw_ptr_exclusion.h"
12
[email protected]997ec9f2012-11-21 04:44:14[diff] [blame]13// base::AutoReset<> is useful for setting a variable to a new value only within
14// a particular scope. An base::AutoReset<> object resets a variable to its
15// original value upon destruction, making it an alternative to writing
16// "var = false;" or "var = old_val;" at all of a block's exit points.
[email protected]5be7da242009-11-20 23:16:26[diff] [blame]17//
[email protected]997ec9f2012-11-21 04:44:14[diff] [blame]18// This should be obvious, but note that an base::AutoReset<> instance should
19// have a shorter lifetime than its scoped_variable, to prevent invalid memory
20// writes when the base::AutoReset<> object is destroyed.
21
22namespace base {
[email protected]5be7da242009-11-20 23:16:26[diff] [blame]23
Jan Wilken Dörriebcc12592019-10-11 18:26:53[diff] [blame]24template <typename T>
Peter Kastingb0bac5d2023-03-08 21:26:56[diff] [blame]25class [[maybe_unused, nodiscard]] AutoReset {
[email protected]5be7da242009-11-20 23:16:26[diff] [blame]26 public:
Jan Wilken Dörriebcc12592019-10-11 18:26:53[diff] [blame]27 template <typename U>
28 AutoReset(T* scoped_variable, U&& new_value)
[email protected]5be7da242009-11-20 23:16:26[diff] [blame]29 : scoped_variable_(scoped_variable),
Jan Wilken Dörriebcc12592019-10-11 18:26:53[diff] [blame]30 original_value_(
31 std::exchange(*scoped_variable_, std::forward<U>(new_value))) {}
[email protected]0fbd70332010-06-01 19:28:34[diff] [blame]32
Peter Kasting0bca80f2023-03-07 04:37:55[diff] [blame]33 // A constructor that's useful for asserting the old value of
34 // `scoped_variable`, especially when it's inconvenient to check this before
35 // constructing the AutoReset object (e.g. in a class member initializer
36 // list).
37 template <typename U>
38 AutoReset(T* scoped_variable, U&& new_value, const T& expected_old_value)
39 : AutoReset(scoped_variable, new_value) {
40 DCHECK_EQ(original_value_, expected_old_value);
41 }
42
Ahmed Fakhry3571b4f52019-05-15 20:55:49[diff] [blame]43 AutoReset(AutoReset&& other)
Jan Wilken Dörriebcc12592019-10-11 18:26:53[diff] [blame]44 : scoped_variable_(std::exchange(other.scoped_variable_, nullptr)),
45 original_value_(std::move(other.original_value_)) {}
46
47 AutoReset& operator=(AutoReset&& rhs) {
48 scoped_variable_ = std::exchange(rhs.scoped_variable_, nullptr);
49 original_value_ = std::move(rhs.original_value_);
50 return *this;
Ahmed Fakhry3571b4f52019-05-15 20:55:49[diff] [blame]51 }
52
53 ~AutoReset() {
Peter Kasting134ef9af2024-12-28 02:30:09[diff] [blame]54 if (scoped_variable_) {
Ahmed Fakhry3571b4f52019-05-15 20:55:49[diff] [blame]55 *scoped_variable_ = std::move(original_value_);
Peter Kasting134ef9af2024-12-28 02:30:09[diff] [blame]56 }
Ahmed Fakhry3571b4f52019-05-15 20:55:49[diff] [blame]57 }
58
[email protected]5be7da242009-11-20 23:16:26[diff] [blame]59 private:
Lukasz Anforowicz877e6222021-11-26 00:03:23[diff] [blame]60 // `scoped_variable_` is not a raw_ptr<T> for performance reasons: Large
61 // number of non-PartitionAlloc pointees + AutoReset is typically short-lived
62 // (e.g. allocated on the stack).
Keishi Hattori488b7602022-05-02 13:09:31[diff] [blame]63 RAW_PTR_EXCLUSION T* scoped_variable_;
Lukasz Anforowicz877e6222021-11-26 00:03:23[diff] [blame]64
[email protected]0fbd70332010-06-01 19:28:34[diff] [blame]65 T original_value_;
[email protected]5be7da242009-11-20 23:16:26[diff] [blame]66};
67
danakjc3762b92015-03-07 01:51:42[diff] [blame]68} // namespace base
[email protected]997ec9f2012-11-21 04:44:14[diff] [blame]69
[email protected]5be7da242009-11-20 23:16:26[diff] [blame]70#endif // BASE_AUTO_RESET_H_