| 1 | /* |
| 2 | * Copyright (C) 2022 Jérémie Galarneau <jeremie.galarneau@efficios.com> |
| 3 | * |
| 4 | * SPDX-License-Identifier: LGPL-2.1-only |
| 5 | * |
| 6 | */ |
| 7 | |
| 8 | #ifndef LTTNG_SCOPE_EXIT_H |
| 9 | #define LTTNG_SCOPE_EXIT_H |
| 10 | |
| 11 | #include <utility> |
| 12 | |
| 13 | namespace lttng { |
| 14 | |
| 15 | namespace details { |
| 16 | /* Is operator() of InvocableType is marked as noexcept? */ |
| 17 | template <typename InvocableType> |
| 18 | struct is_invocation_noexcept |
| 19 | : std::integral_constant<bool, noexcept((std::declval<InvocableType>())())> { |
| 20 | }; |
| 21 | } /* namespace details. */ |
| 22 | |
| 23 | /* |
| 24 | * Generic utility to run a lambda (or any other invocable object) when leaving |
| 25 | * a scope. |
| 26 | * |
| 27 | * Notably, this makes it easy to specify an action (e.g. restore a context) |
| 28 | * that must occur at the end of a function or roll-back operations in an |
| 29 | * exception-safe way. |
| 30 | */ |
| 31 | template <typename ScopeExitInvocableType> |
| 32 | class scope_exit { |
| 33 | public: |
| 34 | /* |
| 35 | * Since ScopeExitInvocableType will be invoked in the destructor, it |
| 36 | * must be `noexcept` lest we anger the undefined behaviour gods. |
| 37 | */ |
| 38 | static_assert(details::is_invocation_noexcept<ScopeExitInvocableType>::value, |
| 39 | "scope_exit requires a noexcept invocable type"); |
| 40 | |
| 41 | explicit scope_exit(ScopeExitInvocableType&& scope_exit_callable) : |
| 42 | _on_scope_exit{ std::forward<ScopeExitInvocableType>(scope_exit_callable) } |
| 43 | { |
| 44 | } |
| 45 | |
| 46 | scope_exit(scope_exit&& rhs) noexcept : |
| 47 | _on_scope_exit{ std::move(rhs._on_scope_exit) }, _armed{ rhs._armed } |
| 48 | { |
| 49 | /* Don't invoke ScopeExitInvocableType for the moved-from copy. */ |
| 50 | rhs.disarm(); |
| 51 | } |
| 52 | |
| 53 | /* |
| 54 | * The copy constructor is disabled to prevent the action from being |
| 55 | * executed twice should a copy be performed accidentaly. |
| 56 | * |
| 57 | * The move-constructor is present to enable make_scope_exit() but to |
| 58 | * also propagate the scope_exit to another scope, should it be needed. |
| 59 | */ |
| 60 | scope_exit(const scope_exit&) = delete; |
| 61 | scope_exit& operator=(const scope_exit&) = delete; |
| 62 | scope_exit& operator=(scope_exit&&) = delete; |
| 63 | scope_exit() = delete; |
| 64 | |
| 65 | void disarm() noexcept |
| 66 | { |
| 67 | _armed = false; |
| 68 | } |
| 69 | |
| 70 | ~scope_exit() |
| 71 | { |
| 72 | if (_armed) { |
| 73 | _on_scope_exit(); |
| 74 | } |
| 75 | } |
| 76 | |
| 77 | private: |
| 78 | ScopeExitInvocableType _on_scope_exit; |
| 79 | bool _armed = true; |
| 80 | }; |
| 81 | |
| 82 | template <typename ScopeExitInvocableType> |
| 83 | scope_exit<ScopeExitInvocableType> make_scope_exit(ScopeExitInvocableType&& scope_exit_callable) |
| 84 | { |
| 85 | return scope_exit<ScopeExitInvocableType>( |
| 86 | std::forward<ScopeExitInvocableType>(scope_exit_callable)); |
| 87 | } |
| 88 | |
| 89 | } /* namespace lttng */ |
| 90 | |
| 91 | #endif /* LTTNG_SCOPE_EXIT_H */ |