| /* |
| * Copyright 2017 Facebook, Inc. |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| #pragma once |
| |
| #include <cstddef> |
| #include <functional> |
| #include <new> |
| #include <type_traits> |
| #include <utility> |
| |
| #include <folly/Portability.h> |
| #include <folly/Preprocessor.h> |
| #include <folly/detail/UncaughtExceptionCounter.h> |
| |
| namespace folly { |
| |
| /** |
| * ScopeGuard is a general implementation of the "Initialization is |
| * Resource Acquisition" idiom. Basically, it guarantees that a function |
| * is executed upon leaving the currrent scope unless otherwise told. |
| * |
| * The makeGuard() function is used to create a new ScopeGuard object. |
| * It can be instantiated with a lambda function, a std::function<void()>, |
| * a functor, or a void(*)() function pointer. |
| * |
| * |
| * Usage example: Add a friend to memory if and only if it is also added |
| * to the db. |
| * |
| * void User::addFriend(User& newFriend) { |
| * // add the friend to memory |
| * friends_.push_back(&newFriend); |
| * |
| * // If the db insertion that follows fails, we should |
| * // remove it from memory. |
| * // (You could also declare this as "auto guard = makeGuard(...)") |
| * ScopeGuard guard = makeGuard([&] { friends_.pop_back(); }); |
| * |
| * // this will throw an exception upon error, which |
| * // makes the ScopeGuard execute UserCont::pop_back() |
| * // once the Guard's destructor is called. |
| * db_->addFriend(GetName(), newFriend.GetName()); |
| * |
| * // an exception was not thrown, so don't execute |
| * // the Guard. |
| * guard.dismiss(); |
| * } |
| * |
| * Examine ScopeGuardTest.cpp for some more sample usage. |
| * |
| * Stolen from: |
| * Andrei's and Petru Marginean's CUJ article: |
| * http://drdobbs.com/184403758 |
| * and the loki library: |
| * http://loki-lib.sourceforge.net/index.php?n=Idioms.ScopeGuardPointer |
| * and triendl.kj article: |
| * http://www.codeproject.com/KB/cpp/scope_guard.aspx |
| */ |
| class ScopeGuardImplBase { |
| public: |
| void dismiss() noexcept { |
| dismissed_ = true; |
| } |
| |
| template <typename T> |
| FOLLY_ALWAYS_INLINE static void runAndWarnAboutToCrashOnException( |
| T& function) noexcept { |
| try { |
| function(); |
| } catch (...) { |
| warnAboutToCrash(); |
| std::terminate(); |
| } |
| } |
| |
| protected: |
| ScopeGuardImplBase() noexcept : dismissed_(false) {} |
| |
| static ScopeGuardImplBase makeEmptyScopeGuard() noexcept { |
| return ScopeGuardImplBase{}; |
| } |
| |
| template <typename T> |
| static const T& asConst(const T& t) noexcept { |
| return t; |
| } |
| |
| bool dismissed_; |
| |
| private: |
| static void warnAboutToCrash() noexcept; |
| }; |
| |
| template <typename FunctionType> |
| class ScopeGuardImpl : public ScopeGuardImplBase { |
| public: |
| explicit ScopeGuardImpl(FunctionType& fn) noexcept( |
| std::is_nothrow_copy_constructible<FunctionType>::value) |
| : ScopeGuardImpl( |
| asConst(fn), |
| makeFailsafe(std::is_nothrow_copy_constructible<FunctionType>{}, |
| &fn)) {} |
| |
| explicit ScopeGuardImpl(const FunctionType& fn) noexcept( |
| std::is_nothrow_copy_constructible<FunctionType>::value) |
| : ScopeGuardImpl( |
| fn, |
| makeFailsafe(std::is_nothrow_copy_constructible<FunctionType>{}, |
| &fn)) {} |
| |
| explicit ScopeGuardImpl(FunctionType&& fn) noexcept( |
| std::is_nothrow_move_constructible<FunctionType>::value) |
| : ScopeGuardImpl( |
| std::move_if_noexcept(fn), |
| makeFailsafe(std::is_nothrow_move_constructible<FunctionType>{}, |
| &fn)) {} |
| |
| ScopeGuardImpl(ScopeGuardImpl&& other) noexcept( |
| std::is_nothrow_move_constructible<FunctionType>::value) |
| : function_(std::move_if_noexcept(other.function_)) { |
| // If the above line attempts a copy and the copy throws, other is |
| // left owning the cleanup action and will execute it (or not) depending |
| // on the value of other.dismissed_. The following lines only execute |
| // if the move/copy succeeded, in which case *this assumes ownership of |
| // the cleanup action and dismisses other. |
| dismissed_ = other.dismissed_; |
| other.dismissed_ = true; |
| } |
| |
| ~ScopeGuardImpl() noexcept { |
| if (!dismissed_) { |
| execute(); |
| } |
| } |
| |
| private: |
| static ScopeGuardImplBase makeFailsafe(std::true_type, const void*) noexcept { |
| return makeEmptyScopeGuard(); |
| } |
| |
| template <typename Fn> |
| static auto makeFailsafe(std::false_type, Fn* fn) noexcept |
| -> ScopeGuardImpl<decltype(std::ref(*fn))> { |
| return ScopeGuardImpl<decltype(std::ref(*fn))>{std::ref(*fn)}; |
| } |
| |
| template <typename Fn> |
| explicit ScopeGuardImpl(Fn&& fn, ScopeGuardImplBase&& failsafe) |
| : ScopeGuardImplBase{}, function_(std::forward<Fn>(fn)) { |
| failsafe.dismiss(); |
| } |
| |
| void* operator new(std::size_t) = delete; |
| |
| void execute() noexcept { |
| runAndWarnAboutToCrashOnException(function_); |
| } |
| |
| FunctionType function_; |
| }; |
| |
| template <typename FunctionType> |
| ScopeGuardImpl<typename std::decay<FunctionType>::type> |
| makeGuard(FunctionType&& fn) noexcept( |
| std::is_nothrow_constructible<typename std::decay<FunctionType>::type, |
| FunctionType>::value) { |
| return ScopeGuardImpl<typename std::decay<FunctionType>::type>( |
| std::forward<FunctionType>(fn)); |
| } |
| |
| /** |
| * This is largely unneeded if you just use auto for your guards. |
| */ |
| typedef ScopeGuardImplBase&& ScopeGuard; |
| |
| namespace detail { |
| |
| #if defined(FOLLY_EXCEPTION_COUNT_USE_CXA_GET_GLOBALS) || \ |
| defined(FOLLY_EXCEPTION_COUNT_USE_GETPTD) || \ |
| defined(FOLLY_EXCEPTION_COUNT_USE_STD) |
| |
| /** |
| * ScopeGuard used for executing a function when leaving the current scope |
| * depending on the presence of a new uncaught exception. |
| * |
| * If the executeOnException template parameter is true, the function is |
| * executed if a new uncaught exception is present at the end of the scope. |
| * If the parameter is false, then the function is executed if no new uncaught |
| * exceptions are present at the end of the scope. |
| * |
| * Used to implement SCOPE_FAIL and SCOPE_SUCCESS below. |
| */ |
| template <typename FunctionType, bool executeOnException> |
| class ScopeGuardForNewException { |
| public: |
| explicit ScopeGuardForNewException(const FunctionType& fn) |
| : function_(fn) { |
| } |
| |
| explicit ScopeGuardForNewException(FunctionType&& fn) |
| : function_(std::move(fn)) { |
| } |
| |
| ScopeGuardForNewException(ScopeGuardForNewException&& other) |
| : function_(std::move(other.function_)) |
| , exceptionCounter_(std::move(other.exceptionCounter_)) { |
| } |
| |
| ~ScopeGuardForNewException() noexcept(executeOnException) { |
| if (executeOnException == exceptionCounter_.isNewUncaughtException()) { |
| if (executeOnException) { |
| ScopeGuardImplBase::runAndWarnAboutToCrashOnException(function_); |
| } else { |
| function_(); |
| } |
| } |
| } |
| |
| private: |
| ScopeGuardForNewException(const ScopeGuardForNewException& other) = delete; |
| |
| void* operator new(std::size_t) = delete; |
| |
| FunctionType function_; |
| UncaughtExceptionCounter exceptionCounter_; |
| }; |
| |
| /** |
| * Internal use for the macro SCOPE_FAIL below |
| */ |
| enum class ScopeGuardOnFail {}; |
| |
| template <typename FunctionType> |
| ScopeGuardForNewException<typename std::decay<FunctionType>::type, true> |
| operator+(detail::ScopeGuardOnFail, FunctionType&& fn) { |
| return |
| ScopeGuardForNewException<typename std::decay<FunctionType>::type, true>( |
| std::forward<FunctionType>(fn)); |
| } |
| |
| /** |
| * Internal use for the macro SCOPE_SUCCESS below |
| */ |
| enum class ScopeGuardOnSuccess {}; |
| |
| template <typename FunctionType> |
| ScopeGuardForNewException<typename std::decay<FunctionType>::type, false> |
| operator+(ScopeGuardOnSuccess, FunctionType&& fn) { |
| return |
| ScopeGuardForNewException<typename std::decay<FunctionType>::type, false>( |
| std::forward<FunctionType>(fn)); |
| } |
| |
| #endif // native uncaught_exception() supported |
| |
| /** |
| * Internal use for the macro SCOPE_EXIT below |
| */ |
| enum class ScopeGuardOnExit {}; |
| |
| template <typename FunctionType> |
| ScopeGuardImpl<typename std::decay<FunctionType>::type> |
| operator+(detail::ScopeGuardOnExit, FunctionType&& fn) { |
| return ScopeGuardImpl<typename std::decay<FunctionType>::type>( |
| std::forward<FunctionType>(fn)); |
| } |
| } // namespace detail |
| |
| } // folly |
| |
| #define SCOPE_EXIT \ |
| auto FB_ANONYMOUS_VARIABLE(SCOPE_EXIT_STATE) \ |
| = ::folly::detail::ScopeGuardOnExit() + [&]() noexcept |
| |
| #if defined(FOLLY_EXCEPTION_COUNT_USE_CXA_GET_GLOBALS) || \ |
| defined(FOLLY_EXCEPTION_COUNT_USE_GETPTD) || \ |
| defined(FOLLY_EXCEPTION_COUNT_USE_STD) |
| #define SCOPE_FAIL \ |
| auto FB_ANONYMOUS_VARIABLE(SCOPE_FAIL_STATE) \ |
| = ::folly::detail::ScopeGuardOnFail() + [&]() noexcept |
| |
| #define SCOPE_SUCCESS \ |
| auto FB_ANONYMOUS_VARIABLE(SCOPE_SUCCESS_STATE) \ |
| = ::folly::detail::ScopeGuardOnSuccess() + [&]() |
| #endif // native uncaught_exception() supported |